Unconventional shallow biogenic gas systems

Unconventional shallow biogenic gas systems

George W.Shurr and Jennie L.Ridgley

A B S T R A C T

Unconventional shallow biogenic gas falls into two distinct systems that have different attributes.Early-generation systems have blan-ketlike geometries,and gas generation begins soon after deposition of reservoir and source https://www.wendangku.net/doc/0f18466201.html,te-generation systems have ringlike geometries,and long time intervals separate deposition of reservoir and source rocks from gas generation.For both types of systems, the gas is dominantly methane and is associated with source rocks that are not thermally mature.

Early-generation biogenic gas systems are typi?ed by produc-tion from low-permeability Cretaceous rocks in the northern Great Plains of Alberta,Saskatchewan,and Montana.The main area of production is on the southeastern margin of the Alberta basin and the northwestern margin of the Williston basin.The huge volume of Cretaceous rocks has a generalized regional pattern of thick,non-marine,coarse clastics to the west and thinner,?ner grained marine lithologies to the east.Reservoir rocks in the lower part tend to be ?ner grained and have lower porosity and permeability than those in the upper part.Similarly,source beds in the lower units have higher values of total organic carbon.Patterns of erosion,deposi-tion,deformation,and production in both the upper and lower units are related to the geometry of lineament-bounded basement blocks.Geochemical studies show that gas and coproduced water are in equilibrium and that the?uids are relatively old,namely,as much as66Ma.Other examples of early-generation systems in-clude Cretaceous clastic reservoirs on the southwestern margin of Williston basin and chalks on the eastern margin of the Denver basin.

Late-generation biogenic gas systems have as an archetype the Devonian Antrim Shale on the northern margin of the Michigan basin.Reservoir rocks are fractured,organic-rich black shales that also serve as source rocks.Although fractures are important for production,the relationships to speci?c geologic structures are not https://www.wendangku.net/doc/0f18466201.html,rge quantities of water are coproduced with the gas,and geochemical data indicate that the water is fairly fresh and rela-tively young.Current thinking holds that biogenic gas was gener-ated,and perhaps continues to be,when glacial meltwater

Copyright?2002.The American Association of Petroleum Geologists.All rights reserved. Manuscript received June21,2001;revised manuscript received June6,2002;?nal acceptance June6, 2002.A U T H O R S

George W.Shurr?GeoShurr Resources, LLC,Rt.1,Box91A,Ellsworth,Minnesota, 56129;geoshurr@https://www.wendangku.net/doc/0f18466201.html, George W.Shurr is an independent geologist and partner in GeoShurr Resources,LLC.He recently retired from a thirty-year career of university teaching and consulting.His B.A. degree is from the University of South Dakota, his M.S.degree is from Northwestern University,and his Ph.D.is from the University of Montana.His research interests include shallow gas systems on basin margins, lineament block tectonics,and Cretaceous stratigraphy in the northern Great Plains. Jennie L.Ridgley?U.S.Geological Survey, Box25046,MS939,Denver,Colorado, 80225-0046;ridgley@https://www.wendangku.net/doc/0f18466201.html,

Jennie Ridgley received her B.S.degree in mathematics from Pennsylvania State University and M.S.degree in geology from the University of Wyoming.She has been employed with the U.S.Geological Survey since1974.Recently she headed a multidisciplinary team project to reassess the shallow biogenic gas potential of Montana. Her most recent research has focused on understanding the genesis and controls on shallow biogenic gas accumulation in Montana,Alberta,and Saskatchewan.

A C K N O W L E D G E M E N T S

This article has bene?ted greatly from input by a diverse group of geologists.John Curtis and Ben Law were editors for this collection of articles on unconventional gas systems. Mark Longman and Jim Minelli acted as AAPG reviewers.Richard Pollastro and Charles Spen-cer also gave detailed reviews.Industry geolo-gists who read an early version of the article and provided helpful suggestions included Da-vid Fischer,Dale Leckie,Timothy Maness,and James Morabito.

AAPG Bulletin,v.86,no.11(November2002),pp.1939–19691939

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Unconventional Shallow Biogenic Gas

Systems

Figure 1.Sketch of a generic basin,comparing the location of shallow,biogenic gas accumulations above the ?oor with the location of deep,thermogenic accumulations below the ceiling.

descended into the plumbing system provided by frac-tures.Other examples of late-generation systems in-clude the Devonian New Albany Shale on the eastern margin of the Illinois basin and the Tertiary coalbed methane production on the northwestern margin of the Powder River basin.

Both types of biogenic gas systems have a similar resource development history.Initially,little technol-ogy is used,and gas is consumed locally;eventually,sweet spots are exploited,widespread unconventional reservoirs are developed,and transport of gas is inter-state or international.However,drilling and comple-tion techniques are very different between the two types of systems.Early-generation systems have water-sensitive reservoir rocks,and consequently water is avoided or minimized in drilling and completion.In contrast,water is an important constituent of late-gen-eration systems;gas production is closely tied to de-watering the system during production.

Existing production and resource estimates gen-erally range from 10to 100tcf for both types of bio-genic gas systems.Although both system types are ex-amples of relatively continuous accumulations,the geologic frameworks constrain most-economic produc-tion to large geologic structures on the margins of basins.Shallow biogenic gas systems hold important resources to meet the increased domestic and inter-national demands for natural gas.

I N T R O D U C T I O N

Unconventional shallow biogenic gas systems represent resources that commonly are unappreciated or even neglected as possible solutions for increased natural gas demands.Wells completed in biogenic gas accumula-tions commonly have low delivery rates that tend to discourage many operators.However,the shallow wells are inexpensive to drill and complete,and the accumulations commonly are in relatively undevel-oped frontier areas where leases are easily obtained.Consequently,unconventional shallow biogenic gas systems are ideal for small and independent domestic operators and for developing or emerging countries.

There is,however,a signi?cant problem in our un-derstanding of shallow biogenic gas systems.In contrast with deep and basin-centered gas systems,shallow bio-genic gas systems have had relatively little scienti?c in-vestigation.For example,the literature on deep gas sys-tems is much more extensive,and exploration models have been clearly articulated.The purpose of this article is to review the litera-ture devoted to shallow biogenic gas systems,with a particular focus on two production areas:Cretaceous rocks in the northern Great Plains and Devonian shale in northern Michigan.These two areas represent two separate and distinct types of shallow biogenic gas sys-tems.This review is intended to provide the ?rst steps toward recognition of speci?c exploration strategies for shallow biogenic gas systems.

B A

C K G R O U N D

Natural gas systems are vertically arranged into three distinct levels within an idealized basin (Figure 1).The deepest level is the kitchen,where thermogenic gas is generated.The kitchen is bounded at the top by the thermogenic ceiling.At depths below the thermogenic ceiling,conditions are right for generation of thermo-genic gas.The shallowest level is where biogenic gas is generated.This microbe nursery is bounded on the bottom by a biogenic ?oor.At depths above the bio-genic ?oor,the environment is favorable for the mi-crobes that generate biogenic gas.The intermediate level may have gas that has migrated upward from the deep,thermogenic kitchen or biogenic gas that has been progressively buried below the shallow microbe nursery.

Shallow biogenic gas is natural gas generated by anaerobic bacteria from organic-rich,thermally im-mature source rocks.Environmental constraints on the microbes,especially temperature and water composi-tion,provide the biogenic ?oor that is analogous to the thermogenic ceiling over deep,basin-centered gas (Fig-ure 1).Biogenic gas accumulations are located at shal-low depths above the ?oor,especially around the mar-gins of the basin.These shallow biogenic gas accumulations generally are underpressured and host large numbers of low-volume wells.In contrast,ther-

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Figure 2.The Alberta,Michigan,and Denver basins have shal-low,biogenic gas around their margins,as well as deep,ther-mogenic gas in the same stratigraphic unit at the basin’s center.The Williston,Illinois,and Powder River basins have biogenic gas on their margins.An early-generation system and a late-generation system are also located (marked Figures 7and 14,

respectively).

Figure 3.Crossplot of carbon-isotope ratio (d 13C)and deuterium-isotope ratio (d D)for methane from several different reservoir types (modi?ed from Rice,1993a).Values for shale are from Martini et al.(1998).

mogenic gas accumulations at the basin center are deep,exhibit anomalous pressure,and generally have high-volume wells (for a review,see Law [2002]).

Shallow biogenic gas accumulations occur in a va-riety of unconventional reservoir types that also have deep thermogenic gas in the same basin (Figure 2).Low-permeability clastic reservoirs in the Alberta ba-sin have biogenic gas on the southeastern margin (Ridgley et al.,1999)and proli?c thermogenic gas pro-duction in the basin’s center (Masters,1984).Frac-tured shales on the northern margin of the Michigan basin have economic accumulations of biogenic gas,al-though the thermogenic gas at the basin’s center has not yet been demonstrated to be economic (Walter et al.,1997).Low-permeability chalk reservoirs produce biogenic gas on the eastern margin of the Denver basin and thermogenic gas near the basin’s center (Rice,1984a).Coalbed methane in the San Juan basin is dominantly thermogenic but includes a component of secondary biogenic gas along the northern margin (Scott et al.,1994).

Most signi?cant production of shallow biogenic gas comes from depths of less than 2000ft (600m),al-though the depth of the biogenic ?oor may vary from basin to basin and over time within a single basin.A summary of worldwide biogenic gas accumulations gives an average minimum depth of 1800ft (550m)

(Rice,1993a).A review of biogenic gas ?elds in the western United States indicates that the average min-imum depth is about 1600ft (490m)(Rice and Clay-pool,1981).A compilation of attributes for shallow gas accumulations on basin margins in the northern and central Rocky Mountains and adjacent Great Plains (Shurr,2001)shows that most are biogenic and fall into two broad categories:large accumulations that cover more than 1000mi 2(2600km 2)and have an average depth of about 1600ft (490m)and smaller sweet spots that average 16mi 2(41km 2)and have an average depth of about 2000ft (600m).However,the perception of shallow depths also ?uctuates with gas prices,pipeline access,and available technology.Eco-nomic basement is in?uenced by these nongeologic controls,as well as by the constraints of the geologic framework,including reservoir and source rock,geo-logic structure,and geochemistry.

Biogenic gas is dominantly methane,but it may contain up to 2%ethane,propane,butane,and pen-tane (Rice and Claypool,1981).Isotopic analyses are used to verify a biogenic origin because methane-rich gases are also produced by other processes.Isotopic compositions are expressed as ratios relative to analytic standards for 13C and for deuterium in the methane.Ranges in these values are used to distinguish ?elds of composition that commonly characterize biogenic and thermogenic gases (Figure 3).Isotopic compositions of gases from low-permeability clastic reservoirs in the northern Great Plains,low-permeability chalks in the Denver basin,and coal beds in the Powder River basin plot within the ?eld for biogenic gas (Rice,1993a).

Compositions of gas from fractured shales in the north-ern Michigan basin plot within the thermogenic?eld (Figure3).However,deuterium values in the methane do show a linear correlation with those in coproduced water.This relationship,as well as other isotopic data, is interpreted to represent a biogenic origin for the methane on the northern margin of the Michigan basin (Martini et al.,1996).

The generation of biogenic gas has been suggested to follow two broadly different scenarios(Rice, 1993a).Early generation is initiated shortly after de-position of the source and reservoir rocks.Subsequent migration and accumulation of the gas can occur over an extended period of time.Clastics of the northern Great Plains and chalks of the Denver basin are both examples of these ancient biogenic gas https://www.wendangku.net/doc/0f18466201.html,te generation occurs during the last few million years and long after deposition of the source and reservoir rocks. Consequently,there is relatively little time for subse-quent migration and accumulation.The fractured shales of the northern Michigan basin(Martini et al., 1996)and the coal beds of the Powder River basin (Rice,1993b)are examples of late-generation biogenic gas systems.

S Y S T E M D E S C R I P T I O N

Shallow biogenic gas systems can be described usefully in terms of the petroleum system concepts outlined by Magoon and Dow(1994).A petroleum system consists of a pod of active source rock,all of the genetically related petroleum accumulations,and the distribution network of migration paths that connect the source rock pod with the accumulations.Essential elements of a petroleum system include source beds,reservoir rocks,seals,and overburden.The main processes are generation,migration,and accumulation of hydrocar-bons;and trap formation.Elements and processes of petroleum systems are described in terms of spatial as-pects,such as pod geometry,and temporal aspects, such as critical moment.The critical moment is the time that provides the best representation of hydro-carbon generation,migration,and accumulation in a petroleum system.

Shallow biogenic gas systems are,however,uncon-ventional,continuous-type accumulations that do not ?t neatly into all of the general system attributes.For example,the formation of discrete traps and the pres-ence of seals may be relatively unimportant in uncon-ventional biogenic gas systems.In addition,source beds and reservoir rocks are generally very close together within the same stratigraphic unit.Consequently,gen-eration and accumulation occur in close proximity,and migration paths are extremely short.Finally,the over-burden is not a particularly important consideration because it is commonly very thin in shallow biogenic gas systems.

Some shallow biogenic gas accumulations are found in conventional reservoir rocks,and many shal-low gas accumulations are a mix of biogenic and ther-mogenic gases.This discussion,however,focuses on unconventional shallow gas systems that are domi-nantly biogenic gas.The early-generation and late-gen-eration scenarios each constitute separate unconven-tional gas systems with distinctive attributes.In particular,these two systems have contrasting pod ge-ometries and critical moments.

Pod Geometries

Shallow gas accumulations in low-permeability clastic reservoirs in the Cretaceous strata of the northern Great Plains provide an archetype for early-generation biogenic gas systems.The geometry of the active source rock pod corresponds to that of the reservoir, and the reservoir geometry has been characterized as a shallow blanket(Law and Spencer,1993).Such ac-cumulations have large-areal-extent,relatively low-permeability reservoir rocks in close association with source beds and display other attributes of continuous-type gas accumulations(Schmoker,1996).In the sim-plest sense,widely distributed stratigraphic units have remained above the biogenic?oor ever since the initial deposition of source and reservoir rocks and the early generation of biogenic gas.The resulting continuous, or blanket,pod geometry is illustrated schematically in Figure4A.Note that the lower part of formation2is currently below the biogenic?oor for the basin;how-ever,at the time of early generation,that is,shortly after deposition,the unit was above the biogenic?oor. This is a consequence of the paleotectonic subsidence of the basin during generation and deposition.

The pod geometry for late-generation biogenic gas systems(Figure4B)contrasts sharply with that of the early-generation systems.The archetype for late-gen-eration systems is the Devonian Antrim Shale in the northern Michigan basin.The Antrim acts as both source and reservoir.The Antrim pod and the associ-ated biogenic gas accumulations are found in a ring shape near where the shale subcrops beneath glacial sediments around the basin rim.Biogenic gas was gen-

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erated during and after glaciation when relatively fresh water carried microbes down into the source rock pod where conditions were favorable for their survival (Martini et al.,1998).Salinities of formation water provide the main constraint on microbe activity and,hence,de?ne the biogenic ?oor for the pod.The re-sulting ring geometry is in?uenced more by subsidence

and erosion that are substantially postdepositional,rather than by paleotectonism that affected the ge-ometry of the Antrim Shale.

The diagrams in Figure 4represent only an ideal-ized version of pod geometries for early and late bio-genic gas systems.In reality,the Cretaceous blanket geometries are not con?ned to a single basin,as shown in Figure 4A;the blankets extend beyond the Alberta basin and into the Williston and Powder River basins (see Figure 2for locations of basins).Similarly,the An-trim Shale is not as deep in the Michigan basin as shown in Figure 4B.More signi?cantly,from an explo-ration standpoint,although both the blanket and ring geometries are relatively continuous,they have small sweet spots with higher productivity embedded within the larger pod.The speci?cs of these geometric varia-tions are discussed in more detail in the descriptions of the geologic framework for the two representative systems.Critical Moment

The timing of events in a petroleum system can be described (Magoon and Dow,1994)using a standard-ized chart such as those shown in Figure 5.The chart format is modi?ed for unconventional biogenic gas sys-

tems by not including events such as deposition of seal and overburden rock and trap formation.Of particular

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importance is the time that best represents gas gener-ation,migration,and accumulation.The time differ-ence between this critical moment and the deposition of the source-reservoir rock provides another clear con-trast between early-and late-generation systems,in ad-dition to the difference in pod geometries.

Early generation occurs shortly after deposition of the source-reservoir rock in the Cretaceous clastics of the northern Great Plains (Rice and Shurr,1980;Rice and Claypool,1981).Generation,migration,and ac-cumulation occur continuously during deposition of the source-reservoir rock and may continue on into the postdepositional history of the system (Fishman et al.,2001).As a result,the critical moment approximately corresponds to the deposition of the source-reservoir rock and subsequent burial by overburden deposition (Figure 5A).

Late generation of gas in the Devonian Antrim Shale of the Michigan basin is associated with relatively recent glaciation (Martini et al.,1998).Consequently,the critical moment is substantially later than the de-position of the source-reservoir rock in the Late De-vonian (Figure 5B).There is signi?cantly less time for secondary generation,migration,and accumulation when compared with the early-generation system.

In the following sections,the general attributes of early and late shallow biogenic gas systems are aug-mented by descriptions of the geologic framework for the two archetypes:the Cretaceous low-permeability rocks in the northern Great Plains and the Antrim Shale in the northern Michigan basin.Additional ex-amples for each system type are described more brie?y.

G E O L O G I C F R A M E W O R K :E A R L Y -G E N E R A T I O N S Y S T E M

Signi?cant biogenic gas resources are found in shallow Cretaceous reservoirs in southern Alberta and Sas-katchewan and in central and eastern Montana.The gas-prone rocks that cover this large area are part of a complex sedimentary rock package that is thousands of feet thick.Reservoir rocks range in age from Ceno-manian through Campanian (Figure 6).Although the units are spread as a continuous blanket over the entire northern Great Plains,the main hydrocarbon produc-tion is limited to the margins of structural basins:the southeastern margin of the Alberta basin,the north-western and southwestern margins of the Williston

ba-

Figure 6.Correlation chart showing selected Cretaceous rock units from southeastern Alberta,southwestern Saskatchewan,and Montana.Asterisks mark gas-producing formations.The Shannon Sandstone Member (not shown)occurs in the Gammon Shale and is equivalent to sandstones found in the ?ne-grained facies of the Milk River Formation in Alberta and Saskatchewan.

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sin,and the northern margin of the Powder River basin (Figures 2,7).

The huge rock volume can be subdivided into a lower and an upper part on the basis of geologic frame-work,reservoir and source rock attributes,and patterns of development and production.An unconformity at the base of the Niobrara Formation (Figure 6)extends across the northern Great Plains (Dyman et al.,1995).This stratigraphic break separates deposition during contrasting cycles of transgression and regression and during different paleotectonic regimes (Shurr et al.,1989b).The single cycle of transgression and regres-sion that deposited the lower part was fairly symmet-ric;however,the several cycles that deposited the up-per part had rapid transgressions followed by slow regression and progradation.In the lower cycle,reser-voir rocks tend to be ?ner grained and source beds have higher amounts of organic carbon than the reservoir rocks have in the upper cycles.

Resource estimates vary widely.Original estimates of gas in place in the United States part of the system were more than 100tcf (Rice and Shurr,1980);later calculations suggested about 40tcf of technically re-coverable gas (Rice and Spencer,1996).In the Cana-dian part of the system,an early estimate was 15tcf (Rice and Claypool,1981).Differences between the lower and upper cycles are re?ected in summaries for individual areas.In and around Bowdoin dome,the lower cycle has produced about 220bcf (Rice et al.,1990),whereas the upper cycle is relatively unproduc-tive.In southeastern Alberta,the reservoirs in the lower cycle have reserves estimated at less than 3tcf,

10

Malta Pool

Bowdoin dome

Moose Jaw

syncline

but reservoirs in the upper cycles have estimates of almost11tcf(Canadian Gas Potential Committee, 1997).

Lower Cycle Rocks

A single cycle of transgression and regression deposited the formations that constitute the lower part of the Cretaceous blanket reservoirs.From oldest to young-est,these formations are the Belle Fourche Formation, Greenhorn Limestone/Second White Specks Forma-tion,and Carlile Shale(Figure6).

Belle Fourche Formation

The Belle Fourche Formation is one of the principal host formations for shallow biogenic gas in the north-ern Great Plains(Bloch et al.,1999;Ridgley et al., 2001a).Regionally,gas in the Belle Fourche is not pro-duced from the same part of the formation.Patterns of gas production re?ect the distribution and preser-vation of silty and sandy facies at the time that gas was generated,that is,the gas is early generational.The Belle Fourche is divided into a lower and an upper part, each of which has different characteristics(Gilboy, 1988;Ridgley and Gilboy,2001;Ridgley et al.,2001a). The upper part rests on an erosional surface(Figure 8A)that appears to be regionally widespread and that has little relief.Strata overlying this erosional surface differ from strata below with respect to sedimentary structures,vertical stacking of lithology,foraminiferal assemblages,and paleoenvironments.

The lower part of the Belle Fourche,which indus-try also refers to as the Second White Specks Sandstone (Gilboy,1988),is divided(Ridgley et al.,2001a)into three units(A–C in Figure8A).The basal,primarily shale,unit separates the overlying sandy sequences from the underlying Fish Scales and Mowry forma-tions.The two overlying units each consist of a very ?ne grained to locally coarse-grained sandstone at the base that is overlain by shale and shale mixed with thin sandstone lenses(Gilboy,1988;Ridgley and Gilboy, 2001;Ridgley et al.,2001a).Deposition was in shelf environments characterized by low to moderate en-ergy.Regional cross sections show that the sandstone and shale sequences were deposited on and?lled in regional erosional surfaces of variable relief.The relief on the unconformities and the geometry of the depo-sitional packages were affected by movement on fault-bounded basement blocks.Gas is produced from both sandstone units in Saskatchewan in the Southeast Al-berta gas?eld and Wymark pool(Figure7).

The upper part of the Belle Fourche is also sub-divided into three units(D1–D3in Figure8A),based on recognition of three upward-coarsening pro?les observed in wire-line logs from the southern end of Bowdoin dome(Rice,1984b;Rice et al.,1990).Ap-plication of this subdivision is more dif?cult when cor-relations are traced to the north and west,because of facies and thickness changes and because of differential loss of section below an unconformity at the base of the Greenhorn Limestone(Figure8A).In Montana, reservoir units in the upper Belle Fourche are referred to as Mosby or Phillips(Rice and Shurr,1980),and in Canada,the units are referred to as Second White Specks Sandstone by industry(Gilboy,1988).Within each of the major parasequence sets,the best reservoir-quality sandstone(higher porosity and permeability with less clay)is found at the top.These sandy intervals tend to be elongate on a northwest-southeast axis,ap-proximately subparallel to the inferred paleoshorelines that originally lay to the west within the thrust belt. Individual sandstone lenses are imbricate(Ridgley and Gilboy,2001)and pinch laterally into shale(Rice, 1984b).Trends in gas production in Canada have the same northwest-southeast orientation(Figure7),re-?ecting the orientation of the sandy intervals.

The upper part of the Belle Fourche was mostly deposited in shelf environments(Rice and Shurr,1980; Rice,1984b).The clastics appear to have been derived from western Montana and eastern Idaho(Ridgley et al.,2001a).As with the lower part of the Belle Fourche,the thickness and geometry of reservoir units are controlled by preservation beneath a regional un-conformity,namely,that at the base of the Greenhorn and Second White Specks,and by movement on line-ament-bounded basement blocks.For example,unit D3(Figure8A)is best developed in the southern Bow-doin dome area;it is truncated by the unconformity to the north and west beneath the Greenhorn.As a con-sequence,the reservoir is areally restricted.Production on Bowdoin dome comes from all three sandy units in the upper Belle Fourche,but in Canada most of the production is from unit D2,because unit D3has been removed by erosion.

Greenhorn Limestone/Second White Specks Formation Throughout their geographic extent in the shallow gas-producing area of Montana,Alberta,and Saskatche-wan,the Greenhorn Limestone and Second White Specks Formation consist of gray,calcareous,white-speckled,coccolith-bearing?ssile shale.Some strata in southern Alberta and Saskatchewan,formerly called

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the Second White Speckled Shale or Second White Speckled Sandstone(industry usage),are now assigned to the Belle Fourche Formation(Bloch et al.,1993). The base of the Second White Specks is taken to be at the base of the lowest widespread bioclastic limestone bed.The lithologic break between the Greenhorn/Sec-ond White Specks and the underlying Belle Fourche Formation is a regional unconformity(Figure8A)(Rice et al.,1990;Ridgley et al.,2001a).

Thin bioclastic limestone beds containing abun-dant coccoliths and?sh debris are commonly observed in cores.The limestones and the associated shale form parasequences that consist of a basal shale;a middle, transitional interval of thinly interbedded shale and limestone;and a thicker bed of bioclastic limestone at the top.A prominent bentonite occurs in the basal part of the formation(Gilboy,1988).

Production patterns in the Greenhorn Limestone are related to the geometry of lineament blocks.Thick calcarenites provide better reservoir capacity to host gas,and Greenhorn thickness is probably controlled,in part,by block movement(Ridgley et al.,2001a).Lo-cally thick accumulations of calcarenites and bioclastic limestone result from gradual block subsidence.On Bowdoin dome,production is concentrated on the north end(Rice et al.,1990),where wells penetrate a relatively thick Greenhorn section.On a large scale,gas traps appear to be related to block geometry that has controlled reservoir lithology and thickness.On a smaller scale,gas is trapped in the more porous calcar-enites and bioclastic limestone by interbedded benton-ite and shale beds that reduce permeability to gas mi-gration.In Canada,similar lithologic and thickness variations in the Second White Specks Formation are attributed to paleotectonism on lineament blocks (Ridgley and Gilboy,2001;Ridgley et al.,2001a). However,these intervals are rarely the sole target for gas exploration.Tests are commonly done in conjunc-tion with tests of the upper part of the Belle Fourche Formation.Any production from the Second White Specks would be commingled with production from the upper Belle Fourche.

Carlile Shale

The Carlile Shale thickens westward from Bowdoin dome into southeastern Alberta and thins to the north in southwestern Saskatchewan(Rice,1981;Gilboy, 1989a,1993).Its contact with the underlying Green-horn Limestone or Second White Specks Formation is conformable or unconformable,depending on the ef-fect of localized tectonics(Figure8A).Wire-line logs through the Carlile show several upward-coarsening sequences(Figure8A),although their exact nature is poorly understood because of lack of core.Thickness variations in these upward-coarsening sequences re-?ect regional erosional surfaces.

Two areas of shelf sandstone occur within the Car-lile in Montana(Rice and Shurr,1980).The northern area of shelf sandstone is represented by the Bowdoin sandstone and the southern area is equivalent to the Turner Sandy Member.Thus far,only the Bowdoin sandstone has produced biogenic gas.Other sandstone sequences have not been exploration targets,and,con-sequently,the potential for gas in the Carlile is largely unknown.

The Bowdoin sandstone is areally restricted to parts of north-central Montana and southwestern Saskatchewan(Rice,1981;Gilboy,1989a,1993).Pro-duction is restricted to Bowdoin dome,although wire-line log responses indicate similar lithologic character-istics for the Bowdoin sandstone west and north of the dome.On Bowdoin dome,sandstone less than1in.(25 mm)thick is interbedded with siltstone and organic-rich black shale(Nydegger et al.,1980;Rice and Shurr, 1980;Rice et al.,1990).The total sandy-silty interval is more widespread than are individual sandstone lay-ers that are laterally discontinuous(Rice,1981;Gilboy, 1989a).Productive zones appear to contain more clay and are not the cleanest intervals shown on wire-line logs.Localized areas have porosity and permeability values characteristic of conventional reservoirs.How-ever,the producing intervals are generally tight reser-voirs that are improved by both natural and induced fracturing.

Upper-Cycle Rocks

The upper part of the extensive Cretaceous rocks cov-ering the northern Great Plains was deposited in three cycles of transgression and regression/progradation. However,only the?rst two cycles have commercial gas production.Reservoir units have different names in Canada and the United States(Figure6):the Medicine Hat Sandstone and Martin sandy zone of the Niobrara; the Milk River Formation and Eagle Sandstone;and the Belly River and Judith River formations.

Niobrara Formation

Regionally,the Niobrara Formation thickens toward the northwest from Montana into Alberta and thins to the north in Saskatchewan(Rice,1981;Gilboy,1989a, 1996).The Niobrara is dominantly a gray,calcareous,

1948Unconventional Shallow Biogenic Gas Systems

coccolithic shale informally known in Canada as the First White Speckled shale.Shallow biogenic gas is pro-duced from sandy intervals in the Medicine Hat and Martin.Principal production has been from the Med-icine Hat in the Southeast Alberta gas?eld(Figure7).

The Medicine Hat Sandstone in Alberta and Sas-katchewan is an interval of thin sandstone,siltstone, and interbedded mudstone in the upper100ft(30m) of the Niobrara Formation(Hancock and Glass,1968; Gilboy,1989b;Hankel et al.,1989;Schro¨der-Adams et al.,1997,1998;O’Connell,1999).The Medicine Hat is composed of a series of upward-coarsening para-sequences;the principal gas-bearing intervals are units A,C,and D(Figure8B).Units C and D are localized in southwestern Saskatchewan and adjacent areas of northern Montana and southern Alberta.The Medi-cine Hat A unit contains the greatest volume of bio-genic gas and is also the most regionally extensive.It thins to the north and east in Saskatchewan and to the northwest in Alberta(Rice,1981;Gilboy,1989a, 1996;Schro¨der-Adams et al.,1997).Overall,the Med-icine Hat sands are composite units consisting of?ne-grained sandstone and siltstone interlaminated with thin mudstone beds.Sandstone bodies are elongate on a northwest-southeast trend(Gilboy,1989b),subpar-allel to the shoreline located in western Alberta(Rob-erts and Kirschbaum,1995).The Medicine Hat was deposited in shallow shelf environments that were in-?uenced by broad and regional syndepositional tecton-ism on the Sweetgrass arch(Nielson and Schro¨der-Adams,1999).

The Martin sandy zone in the Bowdoin dome area consists of thin,sandy lenses in the upper part of the Niobrara Formation(Nydegger et al.,1980).On re-gional cross sections,the Martin is the lateral equiva-lent of the upper Medicine Hat A and undifferentiated Niobrara above the Medicine Hat A unit(Rice,1981; Simpson,1981;Gilboy,1989b).Limited available core data show that the unit consists of thinly interbedded sandstone,siltstone,and shale.Wire-line logs indicate that thick and elongate sandstone bodies,such as those hosting Medicine Hat pools in Canada,are absent from the Martin.On Bowdoin dome,old wells tested gas from the Martin,but commercial production has only recently been established in a few wells on Bowdoin dome and at Battle Creek?eld(Figure7).

Milk River Formation/Eagle Sandstone

The Milk River Formation in Canada consists of sand-stone,argillaceous siltstone,mudstone,and occasional lignite and bentonite beds(Meijer-Drees and Myhr,1981).In eastern Alberta,the formation is divided into the Telegraph Creek,Virgelle,and Dead Horse Coulee members.Some biogenic gas has been produced from the Telegraph Creek Member,which is a succession of offshore marine mudstone and thin-bedded,laminated sandstone.The overlying Virgelle and Dead Horse Coulee members document the successive seaward progradation of shoreface sandstones and rocks de-posited in transitional tidal,deltaic,and estuarine en-vironments.This culminates with heterogeneous and carbonaceous lithologies formed in nonmarine envi-ronments.These units have not produced commercial gas,although small amounts of gas are coproduced with water from the Virgelle sandstones.Environmen-tal interpretations(McCrory and Walker,1986;Cheel and Leckie,1990;Meyer et al.,1998)and stratigraphic correlations(Simpson and Singh,1980;Meijer-Drees and Myhr,1981;Gilboy,1987;Ridgley,2000)for these three members provide the context for the lat-erally equivalent,?ne-grained units of the Milk River that produce gas in the Southeast Alberta gas?eld(Fig-ure7).

The principal gas-bearing,?ne-grained Milk River units are diachronous with the coarser Virgelle and Dead Horse Coulee members(O’Connell et al.,1999; Payenburg,2000;Ridgley,2000).In the gas-producing area,the Milk River Formation has been divided into seven lithofacies in the Southeast Alberta gas?eld (Ridgley,2000).Log responses on a typical wire-line log are shown in Figure8C.Lithofacies are interpreted to have been deposited in offshore to inner shelf en-vironments(I–V)and in shoreface and shoreline set-tings(VI and VII).The main gas production occurs in the inner-to outer-shelf and shelf-sandstone facies(III and IV).Although the uppermost amalgamated shore-line sandstone and mudstone facies(VII)also has po-tential,it has not been a historic exploration target to date.

At least two unconformities have been docu-mented in the Milk River Formation.The lower un-conformity(B in Figure9A)occurs between facies II and V(Figure8C)and is characterized by the presence of chert pebbles(O’Connell et al.,1999;Ridgley, 2000).The upper unconformity(A in Figure9A),be-tween facies III and VII(Figure8C),occurs within Campanian strata,and its presence documents signi?-cant movement on the Sweetgrass arch during the Campanian.This unconformity merges with the un-conformity(as a ravinement surface)at the base of the Pakowki Formation in the area of the Sweetgrass arch (Ridgley,2000).

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1950

Unconventional Shallow Biogenic Gas

Systems

Figure 9.Cross section through the Milk River Formation and the Alderson Member of the Lea Park Formation,in the area of the southeast Alberta gas ?eld.(A)Schematic relationship between coastal facies of the Dead Horse Coulee Member and shoreface sandstone of the Virgelle Member of the Milk River Formation to the basinal ?ne-grained facies of the Alderson Member of the Lea Park Formation.Vertical line separates the current gas-producing area from the nonproductive area.(B)Map showing location of cross section.Hatched line represents the seaward extent of shoreface sandstone (Meijer-Drees and Myhr,1981).

The respective ages of the strata above and below the lower unconformity are not well documented.O’Connell et al.(1999)have proposed that coarse-grained Santonian units are cut out below the uncon-formity and that ?ne-grained Campanian rocks were deposited directly above the unconformity (B1in Fig-ure 9A).In this model,gas is trapped in the ?ne-grained facies across the unconformity.This tends to inhibit updip gas migration (O’Connell et al.,1999),in contrast with interpretations of hydrodynamic gas trapped below updip water (Berkenpas,1991;Leis and Letourneau,1995).

Also possible,however,is that the lower uncon-formity occurs within Santonian rocks (B2in Figure 9A)(J.L.Ridgley,2002,unpublished data).To the northeast,the part of the ?ne-grained Lea Park For-mation dated by ammonites as Campanian is well above the lower unconformity (Figure 9A).To the southwest,in the area of Writing-on-Stone Provincial Park (Figure 9B),the Campanian–Santonian boundary is within the coarse-grained Dead Horse Coulee Mem-ber (Figure 9A).In this model,gas is trapped in the ?ne-grained facies as a result of high capillary pressure;however,there would be hydraulic connectivity be-tween the coarse-grained updip facies and the ?ne-grained downdip facies,rather than a discontinuity as proposed by O’Connell et al.(1999).More research is needed to document the age of the strata directly above the lower unconformity,so that hydrologic models can be re?ned.

The Eagle Sandstone in Montana is a clastic wedge of progradational sedimentary rock that separates the underlying transgressive Niobrara Formation from the overlying transgressive Claggett Formation (Rice,

1980;Rice and Shurr,1983).The Eagle of north-cen-tral Montana may be older than strata assigned to the Eagle in southern and eastern Montana(Payenburg, 2000).The two depositional systems were separated by a prominent paleogeographic embayment(Gautier and Rice,1982).Gas is produced from the Eagle at Tiger Ridge?eld in north-central Montana and from Eagle-equivalent units on Cedar Creek anticline,at Pumpkin Creek?eld,and at Liscom Creek?eld in southeastern Montana(Figure7).The last three ac-cumulations are part of the southwestern margin of the Williston basin and northern margin of the Powder River basin that are discussed in a following section as other examples of early-generation biogenic gas in Cre-taceous reservoirs.

In the Bears Paw Mountain area,the Eagle Sand-stone produces biogenic gas from shoreface sand-stones;a typical wire-line log is shown in Figure8D. In the Bears Paw Mountains,the shoreface sandstones are overlain by tidal-?at,coastal-plain,and nonmar-ine-?uvial sedimentary rocks(Rice,1980).Syndepo-sitional tectonism on basement blocks in?uenced shoreline orientation and sandstone geometry in the Eagle(Shurr and Rice,1986).Eagle reservoirs both north and south of the Bears Paw Mountains have good porosity and permeability and,consequently,are considered to be conventional(Rice and Shurr,1980) reservoirs that contain gas with isotopic characteristics of biogenic gas(Rice,1975;Rice and Claypool,1981). The gas formed early and was initially concentrated in stratigraphic traps that were subsequently broken in fault-bounded traps(Rice and Shurr,1980).The faulted traps are on gravity-induced slide blocks (Baker and Johnson,2000)that compartmentalize production to a high degree.

Belly River Group/Judith River Formation

The Belly River Group in Alberta and Saskatchewan and the Judith River Formation in Montana form a clastic wedge of progradational sedimentary rocks that were shed from uplifted source areas in the western thrust belt.The clastic wedge separates(Figure6)the underlying transgressive Lea Park/Pakowki Formation and Claggett Shale from the overlying transgressive Bearpaw Shale(Shurr et al.,1989a;Eberth and Ham-blin,1993).Most of the reservoirs in the Belly River Group and Judith River Formation are conventional sandstone reservoirs with good porosity and perme-ability.Consequently,trapping mechanisms com-monly are conventional stratigraphic and structural traps.For example,gas is produced from Judith River sandstones in fault-bounded gravity slide blocks in the Tiger Ridge area(Baker and Johnson,2000).

The Belly River Group in Canada is divided into three formations,which are,in ascending order,the Foremost Formation,Oldman Formation,and Dino-saur Park Formation(Hamblin,1997;Bergman and Eberth,1998).The lowest formation has nearshore sandstone and shale that inter?nger laterally with the underlying Lea Park/Pakowki Formation.The middle unit has stacked?uvial channels and associated coal deposits characteristic of alluvial to paralic depositional environments.The uppermost formation has sedimen-tary rocks from a variety of paralic coastal plain envi-ronments;however,sandstones have evidence of tidal processes.Sandstones in the Belly River Group pro-duce gas that may be related to coals.

The Judith River Formation in Montana consists of two generalized subdivisions(Rice and Shurr,1980; Shurr et al.,1989a;Rogers,1993).The lower part is interbedded marine sandstone and shale that are tran-sitional with the underlying Claggett Shale.These clas-tic rocks are low-permeability,tight reservoirs that contain gas locally.The upper part includes marine shoreface and nonmarine?uvial sandstone with minor coal.These lithologies were deposited in nonmarine to shallow-marine environments during the main stages of regression.Sandstones are conventional reservoirs that produce gas at Tiger Ridge?eld.On the south-western margin of the Williston basin,gas is produced from Judith River sandstones on Cedar Creek anticline. Gas shows,reservoir characteristics,and resource po-tential also have been described in the area of Poplar dome(Monson,1995),which is located between Ce-dar Creek anticline and Bowdoin dome(Figure7).

Lineament Block Controls

Deposition and deformation of Cretaceous rocks in the northern Great Plains were controlled by major tec-tonic features that are mosaics of lineament-bounded basement blocks(Anna,1986;Shurr et al.,1989b). Biogenic gas accumulations are controlled by linea-ment blocks in three major ways:(1)patterns of thick-ness and lithology in reservoir rocks and source beds re?ect block geometry;(2)postdepositional deforma-tion along the lineament zones produces structural traps and compartmentalizes the reservoirs;and(3) lineaments are zones of increased fracturing and fault-ing that in?uence?uid migration.

Deformation along lineament zones has been re-lated to geologic structures in the Montana plains

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(Shurr et al.,1989c).A size hierarchy of blocks exists that ranges from major lithosphere blocks bounded by lineament zones down to small constituent blocks within lineament zones(Shurr,2000).On Cedar Creek anticline,gas reservoirs are compartmentalized by the small constituent blocks within a lineament zone.On Poplar dome,tectonism on lineament-bounded blocks effectively compartmentalizes hydro-carbon reservoirs(Shurr and Monson,1995),includ-ing Cretaceous shallow gas reservoirs(Monson, 1995).

Fluid?ow may be enhanced or retarded by faults and fractures within a lineament zone.Sealing faults commonly are developed in clastic intervals that con-tain large amounts of shale.Groundwater movement may result in precipitation of fracture?llings that also inhibit?uid movement.Alternatively,a lineament zone may provide a conduit for cross-formational?ow and/or long-distance lateral migration of water,oil,or gas(Shurr and Watkins,1989).Examples of the cor-respondence of lineaments,gas production,and pres-sure variations have been documented in Cretaceous rocks on Bowdoin dome(Shurr et al.,1993).

Although deformation and?uid?ow are impor-tant aspects of gas accumulations controlled by linea-ment blocks,Cretaceous paleotectonism is the most important in?uencing factor for these early-generated biogenic gas accumulations.Early movements on the lineament blocks in?uenced patterns of deposition and erosion so that thickness and lithology variations in res-ervoirs and source beds follow the block outlines.In addition,paleotectonism on the blocks may set up ini-tial traps that collect the early-generated gas.Subse-quently,the gas distribution may be modi?ed by later geologic and hydrologic processes.The Judith River Formation(Shurr et al.,1989a)and the Eagle Sand-stone(Shurr and Rice,1986)have been demonstrated to be in?uenced by lineament blocks in Montana.More recently,the effects of lineament blocks have been documented in the Greenhorn and Belle Fourche for-mations in Canada(Ridgley and Gilboy,2001;Ridgley et al.,2001a).

Summary of Reservoir and Source Bed Attributes

The attributes of reservoir rocks and source beds in Cretaceous rocks in the northern Great Plains are sum-marized in Tables1and2.In these unconventional gas accumulations,the reservoir rocks and source beds are interbedded,migration distances are short,and source-reservoir rock is an important element of the events chart(see Figure5).

The fundamental subdivision of Cretaceous rocks into lower and upper cycles has expression in the res-ervoir-rock attributes(Table1).In general,the lower-cycle reservoirs are characterized by lower porosity val-ues(?15%)and lower permeability values(10s md) when compared with the upper-cycle porosity(?15%) and permeability values(100s md).This conforms to the generalization that the rocks in the lower cycle are ?ner grained and more clay rich than rocks in the upper cycles.Sandstone reservoirs vary in quality because of changes in rock fabric,such as those produced by bio-turbation.Although some porosity and permeability values in both the lower and upper cycles may be char-acteristic of conventional reservoirs,these represent only localized areas within otherwise tight,continu-ous-type reservoirs.

Table1.Summary of Reservoir Rock Attributes

Stratigraphic Unit Porosity(%)Permeability(md)Reference(s)

Upper Cycle

Judith River Formation15–3010s–100s Shurr et al.,1989a

Eagle Sandstone up to26up to150Rice and Shurr,1980

Milk River Formation14–26?1–259Simpson and Singh,1980Myhr and Meijer-Drees,1976 Niobara/Medicine Hat Sandstone5–370.1–500Martin and Yeung,1991Hankel et al.,1989

Lower Cycle

Carlile/Bowdoin Sandstone8–140.1–0.7Nydegger et al.,1980

Greenhorn6–130.1–6Nydegger et al.,1980

Upper Belle Fourche5–210.1–43.5Gilboy,1988Nydegger et al.,1980

Lower Belle Fourche13–230.4–9Gilboy,1988

1952Unconventional Shallow Biogenic Gas Systems

The upper-and lower-cycle subdivisions also are re?ected in the attributes of source beds(Table2).The lower-cycle rocks generally have higher values of total organic carbon than do the rocks of the upper cycles. Furthermore,hydrogen index values are higher in the lower-cycle rocks than in the rocks of the upper cycle. The differences in hydrogen index indicate differences in the type of organic matter.Lower-cycle source beds are capable of producing both gas and liquid hydro-carbons,whereas rocks of the upper cycle have a greater tendency to generate gas.

Geochemistry of Early-Generation Systems

The critical moment of gas generation,migration,and accumulation is an important distinguishing character-istic for unconventional biogenic gas systems.Geo-chemical data from both gas and water in Cretaceous reservoirs in the northern Great Plains clearly demon-strate that the gas is early generation.

Gas Geochemistry

Gas produced from shallow reservoirs in the Belle Fourche through the Judith River formations is of bio-genic origin and was produced during the breakdown of organic matter by anaerobic bacteria.The d13C iso-topic values of the methane in this gas in the shallow reservoirs of Montana,Alberta,and Saskatchewan range from?64.6to?72‰(Rice,1975;Rice and Claypool,1981;P.G.Lillis,2001,personal commu-nication).In addition,the hydrocarbons in the gas are dominated by methane[C1/(C1–C5)?0.98].Both these characteristics are typical of biogenic gas.Bio-genic gas can form in marine and freshwater environ-ments.Generation of methane by microbial action takes two pathways:carbon dioxide reduction and ac-etate fermentation.Most biogenic methane is probably produced during carbon dioxide reduction by hydro-gen,except in very recent freshwater environments, where acetate fermentation appears to be the preferred pathway for methane generation(Schoell,1980;Whi-ticar et al.,1986).

Carbon isotopes in the methane commonly are used as a criterion for identifying biogenic gas.How-ever,this method is not entirely reliable,because bio-genic gas can have a range of carbon-isotope values, including those normally assigned to mixed gas or ther-mal gas.Because most biogenic gas is formed by carbon dioxide reduction,the isotopic composition of the ini-tial and subsequent carbon in the carbon dioxide is the controlling factor for the isotopic composition of the resulting carbon isotope of the methane.This may vary over geologic time.In marine settings,there is gener-ally a greater fractionation(?50to?75‰)between the carbon-isotope composition of the methane and the carbon-isotope composition of the coexisting car-bon dioxide than that observed in freshwater settings (?40to?50‰)(Whiticar et al.,1986).Figure10 shows the carbon-isotope data of coexisting methane and carbon dioxide pairs of recently sampled gas and coproduced water in the Bowdoin dome and Tiger Ridge(near the Bears Paw Mountains)areas(Figure 11).Dissolved carbon in bicarbonate in water is used because measurable carbon dioxide gas was too small for isotopic analysis.The data fall within the marine depositional setting.Note that,in general,as the car-bon isotope of the methane becomes heavier,the cor-responding carbon isotope of the dissolved carbon also becomes heavier.

The carbon-isotope data also support the premise that the gas is old(Rice,1975;Rice and Claypool, 1981)and began to form and accumulate soon after

Table2.Summary of Source Bed Attributes

Stratigraphic Unit Total Organic Carbon

(%)

Hydrogen Index

(from Rock-Val)Reference(s)

Upper Cycle

Milk River Formation0.56–1.1823–29Ridgely et al.,1999

Niobara/Medicine Hat Sandstone0.5–2.189–152Ridgely et al.,1999Schroder-Adams et al.,1998

Lower Cycle

Greenhorn and Second Specks 1.11–3.6958–420Ridgely et al.,1999Ridgely,1998

Upper and Lower Belle Fourche 1.0–4.040–300Bloch et al.,1999Ridgely,1998

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deposition.A recent petrologic study of the Milk River Formation in the gas-producing area of Alberta and Saskatchewan addresses the question of time and du-ration of gas generation(Fishman et al.,2001).Thin sections of several samples from the Milk River For-mation were examined,and the paragenetic sequence of pore-?lling cements was described.Principal pore-?lling cements are siderite and calcite(ferroan to non-ferroan).Carbon isotopes of the carbon in the siderite and the calcite indicate that they could have been pro-duced as a by-product of methanogenesis.The siderite and carbonate cements also were found to contain methane-bearing?uid inclusions,which suggests that the process of methane generation occurred over a sig-ni?cant period of time(about15m.y.,as reported in Fishman et al.[2001]).Principal production of meth-ane appears to have ceased in the early Tertiary when maximum burial occurred,based on evidence of compaction.

Water Geochemistry

Water in shallow Cretaceous reservoirs is of two types: (1)in-situ water that is coproduced with gas,and(2) water that occurs updip from gas accumulations.The latter has been proposed to form an updip barrier to gas migration in the Medicine Hat Sandstone(Hankel et al.,1989)and the Milk River Formation(Berkenpas, 1991;Lies and Letourneau,1995).Recent studies by the U.S.Geological Survey(P.G.Lillis,2001,personal

1954Unconventional Shallow Biogenic Gas Systems

communication)examined the equilibrium relations between the biogenic gas and its coproduced water. During methane generation by the carbon dioxide re-duction pathway,hydrogen from the water is incor-porated in the methane.The fractionation of hydrogen isotopes between water and the coexisting methane has a linear relationship(Schoell,1980;Whiticar et al., 1986),and this linear relationship can be used to es-tablish whether equilibrium exists between the gas and coproduced https://www.wendangku.net/doc/0f18466201.html,ing this linear relationship,all but three of the sample pairs were found to be in equilibrium.

The129I isotope of iodine was obtained for four of the water samples to date the water.The129I isotope has a half-life of15.7m.y.,and the age of the water can be extrapolated at?ve to six times this rate(G. Snyder,2001,personal communication).The gas and coproduced water appear to be in equilibrium for three of the samples.Deuterium was not obtained in the methane for the fourth sample,and,thus,it is not known whether the gas and coproduced water are in equilibrium.

Samples1and2in Figure11are from the western part of the area.Sample1from the Eagle Sandstone yielded an uncorrected age of65.6Ma,and sample2 from the upper part of the Belle Fourche Formation gave53.6Ma.The location of the samples to the north-east of the thrust belt(Figure7)and the age range of about66to54Ma indicate that?uid movement in the formations may relate to the events in the thrust belt. Sears(2000)has suggested that growth of the imbri-cated thrust system forced?uids out from beneath,and to the front of,the tectonic slab,from about79to59 Ma.These perturbations in the regional?ow system may have extended out to the area of shallow gas pro-duction.Early-generation gas may have migrated and been trapped as a part of the tectonic expulsion of?u-ids from the southwest.In fact,the huge Southeast Alberta gas?eld is strategically located at the northeast end of the Sweetgrass arch(Figure7).Fluids squeezed from under the thrust loading may have migrated northeastward along the trend of the arch and its as-sociated lineaments,mixing with or displacing connate water.Gas generated soon after deposition of Creta-ceous rocks was remobilized and ultimately concen-trated and trapped in the Southeast Alberta gas?eld. This may have been a progressive,multistage process, the dates and the accumulations being just the last ma-jor migration and trapping event.

Samples3and4in Figure11are from farther east near Bowdoin dome.Sample3is from the Belle Fourche Formation in the Canadian Monchy pool,and it yielded an uncorrected age of51.0Ma.Sample4is from the upper part of the Belle Fourche at the south end of Bowdoin dome;its uncorrected age is35.6Ma. The younger sample is from shallow depths in an area where units above the lower Claggett have been re-moved by erosion.Additional sampling in this area is needed to understand the disparity in age of water from the Belle Fourche Formation on and near Bowdoin dome.

On a crossplot of the deuterium isotope vs.the d18O isotope,the coproduced water data set(P.G. Lillis,2001,personal communication)plots below the modern meteoric and the Montana meteoric water lines(Figure12).Also shown on Figure12are copairs of deuterium and oxygen isotopes from the Milk River aquifer(Drimmie et al.,1991)that cluster in three ?elds:

1.Water younger than50,000yr is found closest to

the outcrop and represents the most recent recharge, based on36Cl isotope data(Phillips et al.,1986) 2.Water between50,000and600,000yr is found far-

ther downdip but updip from the main gas?eld, based on36Cl isotope data(Phillips et al.,1986) 3.Older water from the Bow Island Sandstone,which

was beyond the36Cl isotope dating technique(36Cl isotope has a half-life of300,000yr),was consid-ered to approximate the water in the Milk River gas-producing?eld

The crossplot of the deuterium isotope vs.the d18O isotope in the coproduced water from the Eagle Sandstone and Belle Fourche Formation are similar to those obtained from the Bow Island Sandstone,al-though they are consistently more enriched in deute-rium(Figure12).Dating the water using the iodine-isotope technique may be useful in understanding the variability between the deuterium and the d18O iso-tope copair values and how these relate to times of gas generation,duration of gas generation,and time of gas migration and exsolution.

The relatively old ages determined for?uids in Cretaceous reservoirs have implications for the pro-posed hydrodynamic trapping mechanisms.If the pre-liminary ages determined for coproduced water rep-resent the shallow biogenic system,except in areas of active recharge,then updip water may not be a control factor for holding gas in place.Instead,incursion of updip water could be a destructive process that pro-gressively destroys the gas accumulation,along its

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G E O L O G I C F R A M E W O R K:L A T E-

G E N E R A T I O N S Y S T E M

The Devonian Antrim Shale yields signi?cant biogenic gas production on the northern margin of the Michigan basin.Hydrogeochemical studies have demonstrated that the gas was generated in the relatively recent geo-logic past(Martini et al.,1996).Consequently,this ac-cumulation is taken as the archetype for late-genera-tion biogenic gas systems.

In contrast with the early-generation system in the Cretaceous of the northern Great Plains,the Antrim is thin,has little lithologic variability,and possesses a well-developed groundwater?ow system that controls gas generation.The biogenic?oor in the Antrim is de-?ned(1)by contemporary groundwater conditions that provide favorable environments for methanogenic microbes and(2)possibly also by fracture permeabil-ity.The biogenic?oor in the early-generation system depends on environmental conditions that existed at or immediately after the time of deposition.These dif-ferences in timing are associated with pods of gas-gen-erating rocks that have distinctly different shapes(see Figures4,5):the gas-prone Antrim has a ring shape around the basin margin,whereas the Cretaceous gas-prone units are continuous blankets.In both systems, viable commercial production is limited to speci?c parts of basin margins where geologic structures exert in?uence.

Although the Antrim Shale is an example of a frac-tured shale reservoir(Curtis,2002),it is different from other fractured shale plays.The Antrim has a low ther-mal maturity and a high total organic carbon,is thin and shallow,and has large amounts of coproduced wa-ter when compared with other fractured shales(Hill and Nelson,2000).A small thermogenic component is likely in the methane produced on the basin margin; fractured shale production elsewhere tends to be dom-inated by thermogenic gas.Although resource esti-mates for the Antrim have generally included the deeper,thermogenic gas(for example,19tcf recov-erable resources[Dalton,1996]),successful produc-tion is concentrated on the northern margin of the ba-sin.In1999,there were6500Antrim gas wells in the Michigan basin,and production was190bcf(Hill and Nelson,2000).

Biogenic gas production on the northern margin of the Michigan basin(Figure13)is from the Upper De-

vonian Antrim Shale.Below the Antrim,Lower and Middle Devonian rocks are dominantly carbonates; above the Antrim,Upper Devonian and Mississippian units are mainly clastic.However,the overlying mantle of glacial deposits is critical to the hydrogeochemical conditions that result in biogenic gas generation.The

10 km

10 mi

100 m

1000 ft

S N

N

S

B

A

Figure13.(A)Area of late-generation biogenic gas produc-tion on the northern margin of the Michigan basin(modi?ed from Walter et al.,1997).(B)Cross section through the northern margin of the Michigan basin,showing the gas-prone Devonian

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following description of the geologic framework for the late-generation Antrim gas system is largely drawn from a series of publications(Martini et al.,1996, 1998;Walter et al.,1996,1997)that are based on work funded by the Gas Research Institute.

Rocks of the Antrim Shale

The Antrim Shale is divided into four units,starting with the Norwood Member at the base and progressing upward through the Paxton Member,Lachine Mem-ber,and the informal upper Antrim member(Gut-schick and Sandberg,1991a).The main targets for gas production are the Norwood and Lachine members, which act as both source beds and reservoir rock.They are laminated,silty,organic-rich black shales with abundant carbonate concretions.Between the Nor-wood and Lachine,the Paxton consists of interbedded gray calcareous shale and argillaceous limestone.The upper Antrim is also a black shale,but it has few con-cretions,and it intertongues toward the western part of the basin with a gray shale interbedded with lime-stone.It has recently received attention as a secondary exploration target in areas where gas is produced from the Norwood and Lachine members(T.Maness,2001, personal communication).Throughout the area of pro-duction on the northern basin margin,the organic-rich Norwood and Lachine have fairly uniform thicknesses of about30ft(9.1m)and80ft(24m),respectively (Walter et al.,1996).However,thicknesses of all An-trim members are in?uenced by erosional cutout at the base of the overlying glacial sediments(Figure 13B).

The paleogeographic setting of the Devonian An-trim(Gutschick and Sandberg,1991b)is similar to the Cretaceous Western Interior seaway,in which the rocks of the early-generation gas system were depos-ited.During the Late Devonian,a transgression ?ooded the Eastern Interior seaway,and several de-pocenters received laterally equivalent,organic-rich black shales:the Antrim Shale in the Michigan basin, the New Albany Shale in the Illinois basin,and the widespread Chattanooga Shale along the western mar-gin of the Appalachian basin.In the central part of the seaway,times of stagnation and anaerobic conditions produced the Norwood and Lachine members.The other members represent times when prodelta clastics and lime mud prograded into the center of the seaway. The Catskill delta complex prograded westward from the erosion of mountainous uplands in the convergent margin east of the Appalachian basin.At the same time,deltaic sediments prograded eastward from low-lying cratonic source areas along the western seaway margin.

Antrim black shales serve both as source beds for biogenic gas and as reservoir rocks.The Norwood and Lachine members have total organic carbon values of 0.5–24%,and the organic material is dominantly ma-rine.The gray shales of the intervening Paxton Mem-ber have lower total organic carbon(0.3–8%),and the organic material includes a greater abundance of ter-restrial matter(Martini et al.,1998).The shales have a low thermal maturity,as indicated by vitrinite re?ec-tance values.The Antrim Shale generally has low po-rosity,but fractures greatly enhance the effective po-rosity and permeability.Fracture sets constitute the plumbing system for groundwater movement and are an important element of the geologic structure in this late-generation biogenic gas system.

Geologic Structure

In the simplest terms,the geologic structure in the area of production is dominated by a gentle dip south-ward off the northern basin margin(Figure13).De-tailed subsurface mapping shows several small anti-clines superimposed on the regional trend(Walter et al.,1996).The anticlines trend northwest and north-east and plunge southward,down the regional dip. Although little work has been done relating these spe-ci?c structures to large-scale structural blocks or to fracture patterns,fractures have been studied locally because they are critical to the groundwater?ow sys-tem.For example,in?uence of fractures on ground-water?ow could be one of several controls on the depth of the biogenic?oor(T.Maness,2001,personal communication).

Outcrops,deviated core,and borehole-imaging logs have been used to characterize fracture patterns in very limited areas(Walter et al.,1996).The domi-nant directions are northeast and northwest for vertical fractures;there is also a northeast set that has moderate dips.Good agreement exists among the surface and subsurface data sets,although,not unexpectedly,the imaging logs from vertical boreholes provided poor data on the vertical https://www.wendangku.net/doc/0f18466201.html,anic-rich black shales of the Lachine and Norwood members have major throughgoing fractures;gray shales in the other two members have many minor fractures that terminate on bedding contacts.Apotria et al.(1994)suggested that the fracture patterns were regional in nature and not related to speci?c geologic structures.However,dis-

1958Unconventional Shallow Biogenic Gas Systems

50万吨年煤气化生产工艺

咸阳职业技术学院生化工程系毕业论文（设计） 50wt/年煤气化工艺设计 1.引言 煤是由古代植物转变而来的大分子有机化合物。我国煤炭储量丰富，分布面广，品种齐全。据中国第二次煤田预测资料，埋深在1000m以浅的煤炭总资源量为2.6万亿t。其中大别山—秦岭—昆仑山一线以北地区资源量约2.45万亿t，占全国总资源量的94%；其余的广大地区仅占6%左右。其中新疆、内蒙古、山西和陕西等四省区占全国资源总量的81.3%，东北三省占 1.6%，华东七省占2.8%，江南九省占1.6%。 煤气化是煤炭的一个热化学加工过程，它是以煤或煤焦原料，以氧气（空气或富氧）、水蒸气或氢气等作气化剂，在高温条件下通过化学反应将煤或煤焦中的可燃部分转化为可燃性的气体的过程。气化时所得的可燃性气体称为煤气，所用的设备称为煤气发生炉。 煤气化技术开发较早，在20世纪20年代，世界上就有了常压固定层煤气发生炉。20世纪30年代至50年代，用于煤气化的加压固定床鲁奇炉、常压温克勒沸腾炉和常压气流床K-T炉先后实现了工业化，这批煤气化炉型一般称为第一代煤气化技术。第二代煤气化技术开发始于20世纪60年代，由于当时国际上石油和天然气资源开采及利用于制取合成气技术进步很快，大大降低了制造合成

气的投资和生产成本，导致世界上制取合成气的原料转向了天然气和石油为主，使煤气化新技术开发的进程受阻，20世纪70年代全球出现石油危机后，又促进了煤气化新技术开发工作的进程，到20世纪80年代，开发的煤气化新技术，有的实现了工业化，有的完成了示范厂的试验，具有代表性的炉型有德士古加压水煤浆气化炉、熔渣鲁奇炉、高温温克勒炉（ETIW）及干粉煤加压气化炉等。 近年来国外煤气化技术的开发和发展，有倾向于以煤粉和水煤浆为原料、以高温高压操作的气流床和流化床炉型为主的趋势。 2.煤气化过程 2.1煤气化的定义 煤与氧气或（富氧空气）发生不完全燃烧反应，生成一氧化碳和氢气的过程称为煤气化。煤气化按气化剂可分为水蒸气气化、空气（富氧空气）气化、空气—水蒸气气化和氢气气化；按操作压力分为：常压气化和加压气化。由于加压气化具有生产强度高，对燃气输配和后续化学加工具有明显的经济性等优点。所以近代气化技术十分注重加压气化技术的开发。目前，将气化压力在P＞2MPa 情况下的气化，统称为加压气化技术；按残渣排出形式可分为固态排渣和液态排渣。气化残渣以固体形态排出气化炉外的称固态排渣。气化残渣以液态方式排出经急冷后变成熔渣排出气化炉外的称液态排渣；按加热方式、原料粒度、汽化程度等还有多种分类方法。常用的是按气化炉内煤料与气化剂的接触方式区分，主要有固定床气化、流化床气化、气流床气化和熔浴床床气化。 2.2 主要反应 煤的气化包括煤的热解和煤的气化反应两部分。煤在加热时会发生一系列的物理变化和化学变化。气化炉中的气化反应，是一个十分复杂的体系，这里所讨论的气化反应主要是指煤中的碳与气化剂中的氧气、水蒸汽和氢气的反应，也包括碳与反应产物之间进行的反应。 习惯上将气化反应分为三种类型：碳—氧之间的反应、水蒸汽分解反应和甲烷生产反应。 2.2.1碳—氧间的反应 碳与氧之间的反应有： C+O2=CO2（1）

煤气化工艺流程

煤气化工艺流程 1、主要产品生产工艺煤气化是以煤炭为主要原料的综合性大型化工企业，主要工艺围绕着煤的洁净气化、综合利用，形成了以城市煤气为主线联产甲醇的工艺主线。 主要产品城市煤气和甲醇。城市燃气是城市公用事业的一项重要基础设施，是城市现代化的重要标志之一，用煤气代替煤炭是提高燃料热能利用率，减少煤烟型大气污染，改善大气质量行之有效的方法之一，同时也方便群众生活，节约时间，提高整个城市的社会效率和经济效益。作为一项环保工程，（其一期工程）每年还可减少向大气排放烟尘万吨、二氧化硫万吨、一氧化碳万吨，对改善河南西部地区城市大气质量将起到重要作用。 甲醇是一种重要的基本有机化工原料，除用作溶剂外，还可用于制造甲醛、醋酸、氯甲烷、甲胺、硫酸二甲酯、对苯二甲酸二甲酯、丙烯酸甲酯等一系列有机化工产品，此外，还可掺入汽油或代替汽油作为动力燃料，或进一步合成汽油，在燃料方面的应用，甲醇是一种易燃液体，燃烧性能良好，抗爆性能好，被称为新一代燃料。甲醇掺烧汽油，在国外一般向汽油中掺混甲醇5?15勉高汽油的辛烷值，避免了添加四乙基酮对大气的污染。 河南省煤气（集团）有限责任公司义马气化厂围绕义马至洛阳、洛阳至郑州煤气管线及豫西地区工业及居民用气需求输出清洁能源，对循环经济建设，把煤化工打造成河南省支柱产业起到重要作用。 2、工艺总流程简介： 原煤经破碎、筛分后，将其中5?50mm级块煤送入鲁奇加压气化炉，在炉内与氧气和水蒸气反应生成粗煤气，粗煤气经冷却后，进入低温甲醇洗净化装置，除去煤气中的CO2和H2S净化后的煤气分为两大部分，一部分去甲醇合成系统，合成气再经压缩机加压至，进入甲醇反应器生成粗甲醇，粗甲醇再送入甲醇精馏系统，制得精甲醇产品存入贮罐；另一部分去净煤气变换装置。合成甲醇尾气及变换气混合后，与剩余部分出低温甲醇洗净煤气混合后，进入煤气冷却干燥装置，将露点降至-25 C后，作为合格城市煤气经长输管线送往各用气城市。生产过程中产生的煤气水进入煤气水分离装置，分离出其中的焦油、中油。分离后煤气水去酚回收和氨回收，回收酚氨后的煤气水经污水生化处理装置处理，达标后排放。低温甲醇洗净化装置排出的H2S到硫回收装置回收硫。空分

讨论方法

头脑风暴法(Brain Storming，BS法)又称智力激励法、或自由思考法(畅谈法，畅谈会，集思法)头脑风暴法出自“头脑风暴”一词。所谓头脑风暴(Brain-Storming)，最早是精神病理学上的用语，指精神病患者的精神错乱状态而言的。而现在则成为无限制的自由联想和讨论的代名词，其目的在于产生新观念或激发创新设想。 头脑风暴法是由美国创造学家A·F·奥斯本于1939年首次提出、1953年正式发表的一种激发性思维的方法。此法经各国创造学研究者的实践和发展，至今已经形成了一个发明技法群，如奥斯本智力激励法、默写式智力激励法、卡片式智力激励法等等。 在群体决策中，由于群体成员心理相互作用影响，易屈于权威或大多数人意见，形成所谓的“群体思维”。群体思维削弱了群体的批判精神和创造力，损害了决策的质量。为了保证群体决策的创造性，提高决策质量，管理上发展了一系列改善群体决策的方法，头脑风暴法是较为典型的一个。 头脑风暴法有可分为直接头脑风暴法（通常简称为头脑风暴法）和质疑头脑风暴法（也称反头脑风暴法）。前者是在专家群体决策尽可能激发创造性，产生尽可能多的设想的方法，后者则是对前者提出的设想、方案逐一质疑，分析其现实可行性的方法。 采用头脑风暴法组织群体决策时，要集中有关专家召开专题会议，主持者以明确的方式向所有参与者阐明问题，说明会议的规则，尽力创造在融洽轻松的会议气氛。一般不发表意见，以免影响会议的自由气氛。由专家们“自由”提出尽可能多的方案。 头脑风暴法应遵守如下原则： 1．庭外判决原则。对各种意见、方案的评判必须放到最后阶段，此前不能对别人的意见提出批评和评价。认真对待任何一种设想，而不管其是否适当和可行。 2．欢迎各抒己见，自由鸣放。创造一种自由的气氛，激发参加者提出各种荒诞的想法。3．追求数量。意见越多，产生好意见的可能性越大。

煤气化工艺流程

精心整理 煤气化工艺流程 1、主要产品生产工艺 煤气化是以煤炭为主要原料的综合性大型化工企业，主要工艺围绕着煤的洁净气化、综合利用，形成了以城市煤气为主线联产甲醇的工艺主线。 主要产品城市煤气和甲醇。城市燃气是城市公用事业的一项重要基础设施，是城市现代化的重要标志之一，用煤气代替煤炭是提高燃料热能利用率，减少煤烟型大气污染，改善大气质量行之 化碳 15%提 作用。 2 。净化 装置。合成甲醇尾气及变换气混合后，与剩余部分出低温甲醇洗净煤气混合后，进入煤气冷却干燥装置，将露点降至-25℃后，作为合格城市煤气经长输管线送往各用气城市。生产过程中产生的煤气水进入煤气水分离装置，分离出其中的焦油、中油。分离后煤气水去酚回收和氨回收，回收酚氨后的煤气水经污水生化处理装置处理，达标后排放。低温甲醇洗净化装置排出的H2S到硫回收装置回收硫。空分装置提供气化用氧气和全厂公用氮气。仪表空压站为全厂仪表提供合格的仪表空气。 小于5mm粉煤，作为锅炉燃料，送至锅炉装置生产蒸汽，产出的蒸汽一部分供工艺装置用汽

，一部分供发电站发电。 3、主要装置工艺流程 3.1备煤装置工艺流程简述 备煤工艺流程分为三个系统： （1）原煤破碎筛分贮存系统，汽运原煤至受煤坑经1#、2#、3#皮带转载至筛分楼、经节肢筛、破碎机、驰张筛加工后，6~50mm块煤由7#皮带运至块煤仓，小于6mm末煤经6#、11#皮带近至末煤仓。 缓 可 能周期性地加至气化炉中。 当煤锁法兰温度超过350℃时，气化炉将联锁停车，这种情况仅发生在供煤短缺时。在供煤短缺时，气化炉应在煤锁法兰温度到停车温度之前手动停车。 气化炉：鲁奇加压气化炉可归入移动床气化炉，并配有旋转炉篦排灰装置。气化炉为双层压力容器，内表层为水夹套，外表面为承压壁，在正常情况下，外表面设计压力为3600KPa（g），内夹套与气化炉之间压差只有50KPa（g）。 在正常操作下，中压锅炉给水冷却气化炉壁，并产生中压饱和蒸汽经夹套蒸汽气液分离器1

煤化工工艺流程

煤化工工艺流程 典型的焦化厂一般有备煤车间、炼焦车间、回收车间、焦油加工车间、苯加工车间、脱硫车间和废水处理车间等。 焦化厂生产工艺流程 1.备煤与洗煤 原煤一般含有较高的灰分和硫分，洗选加工的目的是降低煤的灰分，使混杂在煤中的矸石、煤矸共生的夹矸煤与煤炭按照其相对密度、外形及物理性状方面的差异加以分离，同时，降低原煤中的无机硫含量，以满足不同用户对煤炭质量的指标要求。 由于洗煤厂动力设备繁多，控制过程复杂，用分散型控制系统DCS改造传统洗煤工艺，这对于提高洗煤过程的自动化，减轻工人的劳动强度，提高产品产量和质量以及安全生产都具有重要意义。

洗煤厂工艺流程图 控制方案 洗煤厂电机顺序启动/停止控制流程框图 联锁/解锁方案：在运行解锁状态下，允许对每台设备进行单独启动或停止；当设置为联锁状态时，按下启动按纽，设备顺序启动，后一设备的启动以前一设备的启动为条件（设备间的延时启动时间可设置），如果前一设备未启动成功，后一设备不能启动，按停止键，则设备顺序停止，在运行过程中，如果其中一台设备故障停止，例如设备2停止，则系统会把设备3和设备4停止，但设备1保持运行。

2.焦炉与冷鼓 以100万吨/年-144孔-双炉-4集气管-1个大回流炼焦装置为例，其工艺流程简介如下：

100万吨/年焦炉_冷鼓工艺流程图 控制方案 典型的炼焦过程可分为焦炉和冷鼓两个工段。这两个工段既有分工又相互联系，两者在地理位置上也距离较远，为了避免仪表的长距离走线，设置一个冷鼓远程站及给水远程站，以使仪表线能现场就近进入DCS控制柜，更重要的是，在集气管压力调节中，两个站之间有着重要的联锁及其排队关系，这样的网络结构形式便于可以实现复杂的控制算法。

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煤气化工艺流程简述 1）气化 a）煤浆制备 由煤运系统送来的原料煤**t/h（干基）（<25mm）或焦送至煤贮斗，经称重给料机控制输送量送入棒磨机，加入一定量的水，物料在棒磨机中进行湿法磨煤。为了控制煤浆粘度及保持煤浆的稳定性加入添加剂，为了调整煤浆的PH值，加入碱液。 出棒磨机的煤浆浓度约65%，排入磨煤机出口槽，经出口槽泵加压后送至气化工段煤浆槽。 煤浆制备首先要将煤焦磨细，再制备成约65%的煤浆。磨煤采用湿法，可防止粉尘飞扬，环境好。 用于煤浆气化的磨机现在有两种，棒磨机与球磨机；棒磨机与球磨机相比，棒磨机磨出的煤浆粒度均匀，筛下物少。 煤浆制备能力需和气化炉相匹配，本项目拟选用三台棒磨机，单台磨机处理干煤量43～53t/h，可满足60万t/a甲醇的需要。 为了降低煤浆粘度，使煤浆具有良好的流动性，需加入添加剂，初步选择木质磺酸类添加剂。 煤浆气化需调整浆的PH值在6～8，可用稀氨水或碱液，稀氨水易挥发出氨，氨气对人体有害，污染空气，故本项目拟采用碱液调整煤浆的PH值，碱液初步采用42％的浓度。 为了节约水源，净化排出的含少量甲醇的废水及甲醇精馏废水均可作为磨浆水。 b）气化 在本工段，煤浆与氧进行部分氧化反应制得粗合成气。 煤浆由煤浆槽经煤浆加压泵加压后连同空分送来的高压氧通过烧咀进入气化炉，在气化炉中煤浆与氧发生如下主要反应： CmHnSr+m/2O2—→mCO+（n/2-r）H2+rH2S CO+H2O—→H2+CO2 反应在6.5MPa（G）、1350～1400℃下进行。 气化反应在气化炉反应段瞬间完成，生成CO、H2、CO2、H2O和少量CH4、H2S等气体。 离开气化炉反应段的热气体和熔渣进入激冷室水浴，被水淬冷后温度降低并被水蒸汽饱和后出气化炉；气体经文丘里洗涤器、碳洗塔洗涤除尘冷却后送至变换工段。

头脑风暴法

应用是要遵循4个原则： 1让参与者畅所欲言，对所提出的方案暂时不做评价和判断； 2.鼓励标新立异，与众不同的观点； 3 以获得方案的数量而非质量为目的，鼓励多种想法，多多益善； 4 鼓励提出补充意见和改进意见。 头脑风暴法的步骤技巧 1、会议实施步骤 会前准备：参与人、主持人和课题任务三落实，必要时可进行柔性训练。设想开发：由主持人公布会议主题并介绍与主题相关的参考情况;突破思维惯性，大胆进行联想;主持人控制好时间，力争在有限的时间内获得尽可能多的创意性设想。 设想的分类与整理：一般分为实用型和幻想型两类。前者是指目前技术工艺可以实现的设想，再用脑力激荡法去进行论证、进行二次开发，进一步扩大设想的实现范围。 幻想型设想再开发：对幻想型设想，再用脑力激荡法进行开发，通过进一步开发，就有可能将创意的萌芽转化为成熟的实用型设想。这是脑力激荡法的一个关键步骤，也是该方法质量高低的明显标志。 2、主持人技巧 主持人应懂得各种创造思维和技法，会前要向与会者重申会议应严守的原则和纪律，善于激发成员思考，使场面轻松活跃而又不失脑力激荡的规则。 可轮流发言，每轮每人简明扼要地说清楚创意设想一个，避免形成辩论会和发言不均;要以赏识激励的词句语气和微笑点头的行为语言，鼓励与会者多出设想，如说：“对，就是这样!”“太棒了!”“好主意!这一点对开阔思路很有好处!”等等;禁止使用下面的话语：“这点别人已说过了!”“实际情况会怎样呢?”遇到人人皆才穷计短出现暂时停滞时，可采取一些措施，如休息几分钟，自选休息方法，散步、唱歌、喝水等，再进行几轮脑力激荡。 或发给每人一张与问题无关的图画，要求讲出从图画中所获得的灵感。根据课题和实际情况需要，引导大家掀起一次又一次脑力激荡的“激波”。如课题是某产品的进一步开发，可以从产品改进配方思考作为第一激波、从降低成本思考作为第二激波、从扩大销售思考作为第三激波等。 又如，对某一问题解决方案的讨论，引导大家掀起“设想开发”的激波，及时抓住“拐点”，适时引导进入“设想论证”的激波。要掌握好时间，会议持续1小时左右，形成的设想应不少于100种。但最好的设想往往是会议要结束时提出的，因此，预定结束的时间到了可以根据情况再延长5分钟，这是人们容易提出好的设想的时候。在1分钟时间里再没有新主意、新观点出现时，智力激励会议可宣布结束或告一段落。 常用的步骤方法 1. 了解组织的决策标准 企业头脑风暴会议中产生的好创意往往无疾而终，原因之一是它们不在组织愿意考虑的范围之内。如果外部环境或者企业政策设定了组织必须遵从的框框，那么，“打破思维框框”的口号就是一种无助于事的劝勉。 2. 提出正确的问题 数十年的学术研究表明，传统的、结构松散的头脑风暴法(“以量取胜——创意越多，成功的可能性就越大!”)不如提供更具结构性的方法1。我们发现，提供结构的最佳方法是利用问题作为催生创意的平台。 3. 选择正确的人员 此处的规则非常简单：挑选那些可以回答您所提出的问题的人。这听起来很好理解，然而，

煤气化制甲醇工艺流程

煤气化制甲醇工艺流程
煤气化制甲醇工艺流程 2008-11-08 10:11 1)气化 a)煤浆制备 由煤运系统送来的原料煤**t/h(干基)(<25mm)或焦送至煤贮斗，经称重给料机控 制输送量送入棒磨机，加入一定量的水，物料在棒磨机中进行湿法磨煤。为了控制煤 浆粘度及保持煤浆的稳定性加入添加剂，为了调整煤浆的 PH 值，加入碱液。
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出棒磨机的煤浆浓度约 65%，排入磨煤机出口槽，经出口槽泵加压后送至气化工 段煤浆槽。 煤浆制备首先要将煤焦磨细，再制备成约 65%的煤浆。磨煤采用湿法，可防止粉 尘飞扬，环境好。 用于煤浆气化的磨机现在有两种，棒磨机与球磨机;棒磨机与球磨机相比，棒磨机 磨出的煤浆粒度均匀，筛下物少。
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煤浆制备能力需和气化炉相匹配，本项目拟选用三台棒磨机，单台磨机处理干煤 量 43,53t/h，可满足 60 万 t/a 甲醇的需要。
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为了降低煤浆粘度，使煤浆具有良好的流动性，需加入添加剂，初步选择木质磺 酸类添加剂。
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煤浆气化需调整浆的 PH 值在 6,8，可用稀氨水或碱液，稀氨水易挥发出氨，氨气 对人体有害，污染空气，故本项目拟采用碱液调整煤浆的 PH 值，碱液初步采用 42,的 浓度。
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为了节约水源，净化排出的含少量甲醇的废水及甲醇精馏废水均可作为磨浆水。 b)气化 在本工段，煤浆与氧进行部分氧化反应制得粗合成气。 煤浆由煤浆槽经煤浆加压泵加压后连同空分送来的高压氧通过烧咀进入气化炉， 在气化炉中煤浆与氧发生如下主要反应:
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CmHnSr+m/2O2—?mCO+(n/2-r)H2+rH2S CO+H2O—?H2+CO2 反应在 6.5MPa(G)、1350,1400?下进行。 气化反应在气化炉反应段瞬间完成，生成 CO、H2、CO2、H2O 和少量 CH4、H2S 等气 体。 离开气化炉反应段的热气体和熔渣进入激冷室水浴，被水淬冷后温度降低并被水 蒸汽饱和后出气化炉;气体经文丘里洗涤器、碳洗塔洗涤除尘冷却后送至变换工段。
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气化炉反应中生成的熔渣进入激冷室水浴后被分离出来，排入锁斗，定时排入渣 池，由扒渣机捞出后装车外运。 气化炉及碳洗塔等排出的洗涤水(称为黑水)送往灰水处理。 c)灰水处理 本工段将气化来的黑水进行渣水分离，处理后的水循环使用。 从气化炉和碳洗塔排出的高温黑水分别进入各自的高压闪蒸器，经高压闪蒸浓缩 后的黑水混合，经低压、两级真空闪蒸被浓缩后进入澄清槽，水中加入絮凝剂使其加
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