Shale Gas play screening and evaluation criteriaMichael D. Burnaman. Wenwu Xia. John Shelton(Harding Shelton Group, Oklahoma City, Oklahoma 73102)Abstract: The uniqueness of shale gas plays is contrasted with conventional oil and gas exploration. Based on our ten yearhistory in shale gas exploration, a practical 17 point list of criteria to use for screening shale gas projects and ranking thatencompasses geoscience, geochemistry, reservoir engineering, drilling, completions and production operations is developed andxplained. Other considerations that will impact shale gas development are identified and discussed. Some key methodologiesto incorporate in the evaluation process are also proposed. The outcome of this proposed screening process, if rigorously applied,should quickly identify the projects that have the most likely chance for success for recommendation to management. Examplesfrom active shale gas plays in the United States are used to support these criteria and references to relevant recent publicationsKey words: shale gas play; criteria; screening; evaluationIntroductiongenerated and intact since their movement, 2)a reservoirIth sufficient porosityConventional oil and gas exploration involves locating commercial amounts of hydrocarbons can be stored andgeographic areas(prospects)where a specific set of produced at economically viable rates, 3)a seal above thegeoscience criteria( known as an active petroleum system) reservoir to stop the vertical migration of hydrocarbons, 4)are present that can provide a mechanism to focus a source rock for the hydrocarbons, usually an organic richcommercial concentrations of hydrocarbons. a shale that has a burial history such that sufficientsophisticated risk evaluation methodology is then used to temperature and pressure has been present to transform therank the prospect quality and likelihood of success of organic kerogen into hydrocarbons and then the expulsiondiscovering commercial hydrocarbons. For almost 100 of them into potential traps stratigraphically adjacent oryears the basic elements of these risking criteria have been structurally higher than the source rock, and 5)timing suchset forth as l)a trapping mechanism, whether structural or that all elements of the system exist both sequentially andstratigraphic, that was present when hydrocarbons were concurrently that the hydrocarbons are preserved. If arAbout the Principal Author: Before Harding Shelton Group. Michael D. Bumaman held management, technology development and technical leadershippositions within Mobil Oil Corporation and its affiliates. He also worked for Gulf Technical Services and Esso Production Research during his universityperiod. He has nearly four decades of experience in Geoscience and Engineering within the upstream petroleum industry in North America, Southeast Asia,the North Sea, West Africa, the former Soviet Union and the Middle East. He has a proven record of finding oil and gas in clastic and carbonate environmentsand in reservoir characterization, both onshore and offshore. He has been involved in shale中國(guó)煤化工 Colorado and Oklahoma,and most recently with the Harding Company in a Bamett Shale joint-venture with Exxos from the University ofHouston in 1974 and BS in Geology also from the University of Houston. He is also a PrinciCNMHwner of Eikonal EnergyInc. and Virtual Geoscience Consultants, Inc. He has authored and co-authored papers in SEGs Leading Edge, AAPG Monographs and other journalsrganized and chaired technical sessions for the AAPG and OTC, and held leadership posts in the Indonesian Petroleum Association, Dallas GeophysicalSociety and Azerbaijan Society of Petroleum Engineersof the elements of the petroleum system is absent(a zero this technical literature. New technology developmentmultiplier)then no hydrocarbons are present at that locale focused on shale gas only is barely 10 years old butand a dry hole results. a significant amount of oil and gas accelerating rapidly. This can only be to our advantage forliterature is devoted to quantification and risk evaluation the evaluation of the shale gas potential of China.of petroleum systems to minimize drilling dry holes and a successful shale gas project will require that certainthus lowering hydrocarbon finding costsminimal technical thresholds be satisfied. There are otherIn contrast, shale gas exploration has a much different considerations that are not easily quantified yet are equallyand usually more predictable risk profile. The gas shale(or important. Different authors have their own set of screeningmudstone as it is more correctly described) itself contains criteria. a typical set of screening parameters from anall of the elements of petroleum risk as described above. company is shown in Figure l. The Figure I criteriaThere is no"zero"component that can preclude success once first step but do not begin to address the wide range ofa shale gas play has been proven. In a proven shale gas other important issues for consideration in evaluation ofexploration locale, the risk changes from"are hydrocarbons any shale gas playpresent and at what volume "to"how quickly can the Figure 2 represents a recent comparison of data for thehydrocarbons be extracted and what will be the cost ofextraction? "The producibility of shale gas is not limited toOrganicRichnessa single prospect but to a large geographic region. Successfulshale gas development then becomes a statistically drivenengineering project. Almost all wells drilled will produce(Productivitygas. The challenge is to develop the proper drilling and ( Mineralogycompletion techniques to optimize the gas production rateversus capital employed and operating costs. ConventionalBrittlenessoil and gas technology development is based on over 100years of technical literature. Shale gas exploration relies on Figure 1 Typical shale gas screening criteria( Curtis, 2008)Gas Shale Basin Fayetteville Barnett Marcellus Haynesville Woodford Lewismated Basin Area.9500011000100001.0006.500105003.000Depth, ft4,0007,00012600012Net Thickness. ft20200211006050200420-3009_1202202203001Depth to Base ofTreatable Water. ft1200~8400~4002000Total Organic Carbon.40-98124.51205-4.0141-14045251230553Gas Content, scf/ ton6022012300-350110033000-3001545Water Production0WellspacingAcresn16040-16040160°405680-320122,500050614roduction25002,70060003,50010020012thousands of cubic feet of g中國(guó)煤化工NOTE: Data derived from various sources and research analysis. Iidentified and confirmed at the time of this paper and has beeHCNMHGwfor the Depth to Base of Treatable Water Data. the data were based onsing informaton t the state s oil andgas agency did not specifically report bTw values in their data base.Figure 2 Parameters of various active US shale gas plays(modified after Arthur et al, 2008)中國(guó)石油勘探20年第3期52most active shale gas plays in the U.S. Figure 3 is another comparisons than just data. We want to develop a meanssimilar compilation but with more parameters contrasted. to rank the different shale gas plays with objective criteriaIt is obviously important to compare shale gas plays to and select the best for chance of exploitation successunderstand their science; however there is more to theLewisThck閉5/D12051:=0Bottom-hole temp tFl104043-1U416z=10.1-B01-080t-08Gas prod (Mctidey1,5001000202-252Figure 3 Propof gas shales(Wang, 2008)Listed and explained below are the specific criteria and development.other considerations that we have developed that we believeare necessary to ensure that the best shale gas plays can be 1 Evaluation Criteriabrought forward as part of a structured, technically rigorousI I Shale thicknessprocess. These criteria consider technical, operational andeconomic issues. Some of these criteria may seem obvious It is the vertical concentration of ToC that is most important,and probably are, others may be more subtle but still not just the overall shale thickness. There should be at leastnportant to overall success. Still other criteria may be so one zone within the shale that has high ToC with at least 150important that their absence or marginal nature may feet continuous thickness This will be a viable target forcondemn the shale as having little if any commercial gas the lateral( dependent on adjacent layered porosity zonespotential, even though many other parameters are very as well) and well within the vertical extent of the hydraulifavorable. The list below is not ordered in importance, fracturing. If the Toc is vertically spred out over 500 to lalthough some of the most obvious components are high 000 feH中國(guó)煤化工 aulic fracturing couldon the list. Other criteria farther down the list may be just be dispCNMHck. The Barnett ShaleImportant inthe final assessment of those project areashuAlicsS iD JUV lL, However, good wells can bewith the best chance of quickly building significant gas present with 200 ft thickness if the organic component is aproduction and a large probable reserves base for future large vertically concentrated fraction of that thickness3 2009 Chuna Petroleum Exploration\Wells in the haynesville shale with very high initial'rates source if %Ro is>1.4 to ensure that the oil has at leastare present that have less than 150 feet of high TOC. been cracked to wet gas or with %Ro >2.0 to ensure1.2 Organic richness, TOC, hydrogen index and kerogen condensate rich gas has been cracked to dry gas. Types Iand ml kerogen require higher HI for comparable gastypevolumes. Figure 4 shows photomicrographs of WoodfordThe ToC should be at least 2%with Type I, I or llI shale cores with kerogen. The photo on the left is of shalekerogen. Higher ToC will result in higher gas-in-place with 35.5% TOC(super rich). The photo on the right isvolumes. Type l(oil prone kerogen) can be a good gas chert with 6. 4% TOC, still very rich.Comer (1992)location OK35 Arbuckle Mtn Uplift25-2S-1E; comer (1987) Fig 7cBlack Shale15E;Comer(1987) Fig 7b-“ Highly compacted. Flattened Tasmanitesspores (TAmorphous Type lorganic matter (AOM)Little or no chertTasmanites spores(T)uncompacted orslightly flattenedearly chert (CT)cementation)Amorphous type llOrganic Matteluncompacted).Well indurated, band tightly sealedUp to 35 TOCUp to 6.4 TOC0.2mm0.2mmFigure 4 Photomicrographs of Woodford shale and chert organics( Comer, 2007)1.3 Thermal maturity(%Ro, Tmax, TR, RockEval1.4 Gas-in-place and reservesVitrinite Reflectance(%Ro)should be >1.0 and <3.0. Gas-in-Place(GIP) is the total gas and is the sum of theEvaluate areas for deep burial and later inversion(uplift) free gas(also known as the absorbed gas)and the adsorbedas currently shallow shales may have been deeply buried gas. The free gas is present in the porosity and provideswith later uplift having higher %Ro than current burial depth the high initial production rates. The adsorbed gas is thatould indicate. Beware of extremely deeply buried shales which is attached to the kerogen and clay plates and isas %Ro >3. 0 is onset of hydrocarbon destruction producing released through time providing the long decliningprobable non-economic gas in place. Figure 5 illustrates production. The free gas and adsorbed gas values arethe relationship between %Ro boundaries, kerogen source deriv..中國(guó)煤化工calibrated log analysis.and hydrocarbon generation. Figure 6 shows the TotaiCNMHGErsq mile. The betterrelationship between kerogen types,hydrocarbon generation. Appendix 1 is a geochemical computed gas-in-place values are presented as standardsummary of gas shale playscubic feet of gas per ton of shale(scf/ton) and then數(shù)靄ZONES OF PETROLEUM GENERATIONAND DESTRUCTIONORGANIC MATTER TYPEAMORPHOUS (OIL). MIXED COALY (GAs)hVCbPEAK OIL GENERATIONhvBhaB8.0PEAK WET GAS GENERATIONHEB3st_ ILFLdR..eSAK DRY GAS GENERATION2.0_WET GAS ELOORModified from Dow.o_DRY_GAS GENERATION LIMI(1977), Houseknechtand Hathon(1987),and Taylor and othersDRY GAS PRESERVATION LIMITw. 192398)Figure 5 %Ro boundaries and hydrocarbon generation( Cardot, 2009)%RoType IType l Type lI-os TypeⅢTmax(c)1.80202.402.602803.00width of bubble relates to amount of HCs producedFigure 6 %Ro, kerogen type and Tmax relationship (devon et al, 2009& Jarvie, 2008)converted to Bcf per square mile (Bcf/sq mi)based on area fracture efficiency and long term stability of the inducedand TOC thickness. Total gas recovery factors per square fractures. High quartz concentration adds to the shalemile will depend greatly on areal well density, hydraulic brittleTV中國(guó)煤化工 unction of Poissonfracturing efficiency, gas composition and other factors. RatioCNMHG Parameters can be1.5 Shale brittlenesspuae Sonic log or dirconventional core measurement. The most productive gasExtreme brittleness is absolutely necessary for hydraulic shales have Poisson's Ratio<0. 25 and Young's Modulus>55 No. 3 2009 China Petroleum Exploration\2.0. These shales exhibit well developed conchoidal orthoclase feldspars) have minimal negative reaction tofractures on the shale cores, like glass. The brittleness drilling and slick water fracture fluid. X-Ray difiractionsupplied by quartz can be significant. The shales often and wireline logs can easily define these constituentshave quartz content >40%, generally siltstone but preferably Sometimes 2% to 4%KCl can be added to the fracturewith a large quartz component of organic origin(sponge fluid to minimize effects of the swelling claysspicules and radiolaria), which also increases the overall1. 8 3D seismic available prior to drillingporosity to store free gas. Lack of brittleness also maycause closure of induced fractures around proppant due to While this is not an attribute of the gas shale, it is anplastic flow of the ductile shale and may lead to casing extremely important component in evaluating drilling riskcollapse as has happened in the Haynesville shale in North and potentially indentifying orientations of regional andLouisiana. Appendix 2 is a photomicrograph of Barnett tectonic fracture swarms. Once drilling of the lateral hasshale showing abundant sponge spicules.begun, any unsuspected fault encountered could resultthe target zone not being easily accessible and could take1.6 Porosityseveral hundred feet of the lateral to get back in zone,The best gas shales have average gas filled porosities of possibly creating a problem later while setting casinggreater than 4.0% with the higher the better. The porosity1.9 Tectonic settingis usually concentrated in laminated zones verticalladjacent to or within the highest TOC. The thin laminations The structural complexity of the overburden and zonesare preserved due to a lack of bioturbation in the anoxic physically adjacent to the gas shale should be at a minimumenvironment. The porosity is generally expressed as Complex overburden structure and faulting can significantlyporosity-ft after wireline log analysis. Appendix 3 is a raise drilling costs. Similar complexity directly above andphotomicrograph of Barnett shale showing laminated quartz below the targeted high TOC and porosity zone can causesiltstone. These concentrations of silt sized quartz make completion failure. This would be caused by fracture fluidexcellent porosity. Many of the high EUR Barnett Shale diverting into faults and natural fracture zones thus losingwells have abundant laminations of quartz with high fracture effectiveness and possibly opening highlyporosity and permeabilitypermeable water zones that can reduce gas production tozero. The Woodford and Fayetteville shale exploration in1. 7 Shale mineral compositionOklahoma and Arkansas(Figure 7)are within Ouachita foldThe gas shales are actually mudstones with particle sizes belt thrust sheets creating drilling and completionranging from clays(<5 microns), through silts(5 to 63 challenges and also limiting EURSmicrons)to sand( 63 microns). They usually have a high1.10 Lateral continuity of shaleconcentration of quartz. Abundant pyrite is a good indicatorof anoxic deep water deposition with an absence of The various screening criteria must bepe reasonablybioturbation. Lots of organic quartz( sponge spicules and consistent and extend over a large area to eventuallyadiolarians)is often present. Appendix 4 shows produce any meaningful development and productioncompositions of shales of different geologic age. Of critical volumes. The Barnett Shale play extends over at least 4importance is what is the type and provenance of the clay 600 sq mi or an area about 55 miles by 85 miles. Gas-in-minerals. Generally clays of the smectite group from mafic plac中國(guó)煤化 Climate recovery snorerock types( Ca plagioclase feldspars )and of volcanic origin excedent on final horizontalhave swelling problems during drilling and hydraulic well lrYHCNMH Gic repeat fracturing offracturing. They generally produce poor gas recoveries. horizontal wells and improved completion techniques. ThisThe kaolinite and illite groups of granitic origin(K is a large resource base within a relatively small area. The中國(guó)石油勘探x09年第3期56100,000 times less permeable than even the tight sandreservoirs with similar porosities. For this reason, the siltswithin the gas shales are in large part responsible for thehigh initial flow rates as their porosity is associated withsome K, however small. Gas Shale recovery factorsSe S y.e from 8% to 15% and can rise significantlyas well spacing is reduced and fracture design and efficiencimproves. Permeability, both vertical and lateral, will beprovide in-situ permeability and greatly enhance EURigure 7 Woodford shale 3D seismic exhibiting reverse faulting ( Wang, 2008)(Devon Energy, 2007). The dip of the Woodford, purple, is lesshomogeneous in cross section. Large offset normal faults, dark 1.12 Pressure gradientgreen,divide the Woodford,'s dip into the basin. The regionalfaults in this study area can have 1200 ft+ throws. The faultsa pressure gradient >0.465 psi/ft is optimum as it willare regional enabling a structural view from 2Dincrease gas-in-place but it should not be so high that overpressure induced drilling problems occur. High formationreason this is possible is because of the general continuity pressure in the Haynesville shale in North Louisiana willof the Barnett, reservoir geology, geochemistry, fluid require use of expensive manmade proppants to overcomeproperties, geological structure and relatively simple proppant crushing due to pressuredrilling condition1. 13 Absolute age of shale1. 11 PermeabilityPaleozoic Era shales such as Barnett,, WoodfordGas shales have very low permeability(K), ranging from Fayetteville and Marcellus(Devonian-Mississippian) with0.001 mD(microDarcy)to 0.00001 mD(nano Darcy). absolute ages of 416 MM to 326 MM years appear to beContrast these Ks with tight sands whose K's usually range the best targets at this time. this is mostly due to shalefrom 0. I mD to 0.001 mD. Figure 8 modified from Cluff, brittleness. The younger shales currently undeet al show permeability measurements on gas shales. development (Jurassic Haynesville-160 mm years andPermeability is plotted versus Porosity for gas shale core Upper Cretaceous Eagle Ford- 100 MM years)may notdata illustrating the four to six orders of magnitude have had enough time to obtain optimal brittleness. thispermeability difference between the tight gas sands and can lead to poor EURs. Even though initial flow rates canluch tighter gas shales. The gas shales are at least be very high, these shales will exhibit even greaterproduction declines than the older gas shales. This may beMeasured Shale Propertiedue to plastic movement of these younger shales over time1.E031 microBararound the proppant which may close, inducing fracturesand cause casing collapse1E91 plooDarey1.14 Logistics of water supplies for hydraulic fracturing中國(guó)煤化工,0o0b1E-15N MH Gnation of fraacturesoure can ue exhausted within aFigure8 Permeability Differences between Tight Sands(Green) week depending on the number of fracture stages employed.and gas Shales(Redd after Cluf et al, 2007)Frac pits"with dimensions of two acres or larger and57 No. 3 2009 Chine Petroleum Explorationdepths of 15 feet are normally prepared at the drill site and even though within an old producing area, has been limitedlined with thick plastic when the location for the drilling in some areasrigs is prepared. The pit is then filled via purchase from a 1.16 Drill sites with easy access and constructionlocal municipal water supply, water well(s) drilledespecially for this purpose, or transported using temporary. In the success case it will be imperative that an aggressivepipelines from other existing water wells, adjacent rivers, drilling program be instituted to bring on gas productionlakes, ponds, streams and rainfall. In the worst(and most as quickly as possible Easy access to drill sites whereexpensive)case water is trucked to the pit. It usually takes multiple wells can be drilled from one drill pad is key asseveral months to collect a suitable water volume. In other will be the location of the frac pits. These multi-well padscases portable"frac tanks", each with a volume of 400 bbl will provide the opportunity to simultaneously fracturere deployed at the well site and filled. It takes 250 frac multiple wells, share production facilities and gatheringtanks to stockpile 100,000 bbls of water so fracs utilizing systems. Consideration of simultaneous drilling andthese tanks may have smaller total fluid volumes due to production from the same well pad will be required forthe extra expense involved. Operators in the Marcellus early production buildup. This would imply that surfaceShale in the appalachian Mountains are required to obtain terrain with minimum relief and a good road system wouldwater well permits that require several months for approval be optimum. Avoid mountainous areas where access isfrom local governments. Figure 9 illustrates frac pits restricted as it will be very hard to quickly ramp up gasadjacent to drill pads in wooded, low relief terrainproduction. This is a central issue in West Virginia andPennsylvania where the complex Appalachian fold beltprovides beautiful scenic views but leaves little room forroads, drill sites and frac pits1. 7 Produced water disposeEnvironmentally safe disposal of large amounts ofproduced fracture fluid and salt water associated with thegas production will be required. The fracture fluid dissolvessalt that is present in the shale. Gas shales usually haveamounts of salt water sourced from other formations thatwere invaded by the hydraulic fracturing. Disposal wellswith highly permeable shallow sandstones accessible atFigure 9 frac pits adjacent to drill pads in low relief terraindepths below the fresh water table are required. These wells(Halliburton, 2008).usually have higher grade casing to extend the usable life1. 15 Transport infrastructure in placeof the well. Produced water can be moved to the disposalwells by either gathering systems or truck. Salt waterLarge diameter gas pipelines and compressor stations gathering systems laid in the same ditch as the gas gatheringwith access to large markets need to be in place or nearby lines to the production pads are the most efficient long termto immediately exploit shale gas development. Somegas projects in the U. S such as the Marcellus shale IH中國(guó)煤化 Tle efficient unloadingrucks can unload withCNMHbeen delayed due to the lack of suitable gas transport touv uayvoul station. This is a keylarge markets. Production from the Barnett Shale was issue for all shale plays in the U.S. and different resolutionsinitially constrained. The Haynesville Shale development, are sought and required中)3582 Other ConsiderationsbTU per cfg)are preferred. Oil and condensate constituentshave much larger molecular size than methane and will2. 1 Repeatabilityrestrict flow of the free gas and especially the absorbed gasas it moves from the kerogen and clay platelets to theVery quickly in the life of the exploration phase, the well pressure sinks at the perforations. Higher BTU values willresults and EURs must become predictably repeatable. In work but the condensate production needs to be less thanthe success case the potential exists that literally thousands four bbl/Mmcfg. The Marcellus Shale has high BTUof wells can be drilled within a single gas shale play. The content which may restrict EURBarnett Shale currently has over 11,000 wells with half ofthese wells drilled within the last four years with many2.4 Gas compositionmore yet to drill. The initial screening criteria must be robust Dry gas with 1,025 BTU per mcf is optimal. Since wesuch that the geological, geochemical and engineering will have prepared a thorough chemical analysis of the shaleparameters can become statistically meaningful and prior to drilling we can also eliminate those areas wherepredictable. This will be extremely important in well the gas will have excessive liquids, CO2 and H,S.Thisplanning and scheduling, drilling rig requirements, would ensure that no gas processing or treating is requiredcompletion resources, infrastructure and transport The Barnett and Fayetteville Shales have this favorable gasdevelopment. Any strategic planning will require this composition. The Marcellus Shale gas requires processinginformation2.5 Economic drill depth2. 2 Fracture barriers may be requiredProbable optimal economics will require a drill depthThe prolific Bamett Shale in some areas directly rests less than 11, 000 ft. It has been shown in the Barnett Shaleon the Ellenburger Limestone(Ordovician age)and is that drill depths as shallow as 7, 500 ft can produce shalealways below the Marble Falls Limestone(Pennsylvanian gas wells with EURs over 5 Bcf. However, the Barnettage). The Ellenburger may have zones of high permeability Shale was initially at a depth of 15, 500 ft where the shalethat will produce significant amounts of water if it is became thermally mature. It was later uplifted to its presentpenetrated by the hydraulic fracturing. The best Barnett depth. The depth of optimal thermal maturity will varyShale production is when the impermeable Viola Limestone dependant on the paleo-confining pressure and temperaturesits between the Barnett Shale and the Ellenburger gradient. Currently the deepest vertical depth for shale gasLimestone with the Barnett capped by the Marble Falls wells in the U.S. is 11, 500 ft in the Haynesville ShaleLimestone. In this situation a perfect set of natural fracture The Mako Basin in Hungary is currently being exploredbarriers above and below the Barnett is present and keeps for shale gas at depths deeper than 18,000 ft. The Barnettthe hydraulic fracturing"in zone. This is generally the Shale in west Texas is at 18, 000 feet in some places witharea of highest EUR. In some cases however, the Barnett very high gas-in-place values and operators are planningsits directly on permeable Ellenburger that produces water to drill it but the additional costs are significant.bbl per mcf gas. In these cases gas production rateso high that it overcomes the water production and hig2.6 Regional and tectonic fracture systems understoodrate wells are present(initial rates over 10 Mmcfgpd and The large scale regional fracture systems need to be re-EUR over 4 Bcf)中國(guó)煤化 Ind conjugate fracture2.3 Hydrocarbon liquids reduce gas EURforCNMHell azimuths andI uc wwnt nacture systems can beGas shales with maturation histories indicating probable determined by seismic interpretation. Combinations ofry gas production(predominantly methane with <1,025 regional and tectonic fractures and their conjugate systems9 No. 3 2009 Chine Petroleum Exploration\Swill be vitally important to the drilling direction and in shales. Where they are available they are preciouseffectiveness of the hydraulic fracturing. The barnett shale Whole core analysis should show conchoidal fracture,has few open fractures but abundant carbonate filled laminations of quartz material, kerogen, filled fracturesfractures. These are often opened by hydraulic fracturing. broken core that was removed directly from the core barrelsignifying highly fractured rock. Shale cores that have2. 7 Low present day temperature gradiedescriptions of"bleeding gas"are significant.This will increase gas-in-place due to the higher gas Wireline log characteristics of gas shale are unique. Highcompressibility at lower temperature. It will also help gamma ray count and low density indicate abundantmitigate any possibility that more expensive oil base drilling kerogen, high resistivity indicates low water saturation,fluids will be requiredneutron-density crossover(limestone matrix) shows3 Evaluation Methodsporosity, and low Pe(photoelectric absorption factor)isabnormal for shales and may indicate quartz siltstoneRapid understanding and contrasting of the petroleumAppendix 5 is an illustration of these characteristicssystems of different areas and basins will be expedited if Burial history plots are important in understanding thean abundance of deep wells with wireline logs, well cuttings basin thermal history. Analysis of the thermal history of aand conventional core are available. ability to access these basin can best be understood by preparation of burial historydata using digital databases will be of utmost importance. plots as described by Guidish et al, 1985. SequenceDaily drilling reports, mud logs, core analyses, and log Stratigraphic Source Rock Mapping helps identifyanalyses are among the data to be analyzedprospective shale gas plays that were once oil or gasReview of mudlogs is usually the first step in analyzing generating source rocks and that may not be located directlya gas shale play Any significant gas shows that are common adjacent to current oil or gas fields. These potentiallyto the same formation over a very large area should be "migrated"gas shales, possibly in lower basinal areas nowclosely investigated. Well site analysis of the cuttings inverted, may be identified using Sequence Stratigraphichould mention that the shale is predominately jet black methodology. Such studies have probably, already beenand greasy, obviously very carboniferous and organic with made in many if not most China basins. Review of thesethe associated high TOC. One of the best ways to judge studies focusing on source rock generation and timingthe organic content is the old driller's technique which is coupled with burial history plots may identify basinal areasto rub the shale in the palm of your hand and hope for a more likely to contain thermally mature and over maturevery jet black staining as if you had rubbed your hand with oil and gas prone source rock areas. Appendix 6(Veeken,an ink marker. The shale should have obvious visual inter- 2007) describes recent depositional models and tectonicbedded quartz clastics, both as grains and of biological setting for source rock development that can be deducedorigin. These will generally be siltstones, but in cases they from Sequence Stratigraphic interpretationcan they actually grade into true sandstones. Shales that4 Conclusionsgrade into a light gray, to brownish gray to brownish colorhave generally low TOC and the associated low gas content. The shale gas potential in China could be huge. TheShales that are absolutely homogenous without inter bedded initial evaluation that has already begun to some extentclastics also tend to be low in gas content. The shape of within many business and academic institutions withinthe cuttings vary radically based on many different factors, Chi中國(guó)煤化τ: gion to begin the firstand are not generally indicative of high or low gas content. shahCNML cown that this evaluationThe cuttings description should also include abundaorganized, technicallypyrite, abundant gas shows while drillingstructured process based on proven fundamental conceptsIn the past, few whole cores have been deliberately taken of geoscience and engineering中國(guó)石油年第3期60[11]Jarvie, D, 2008b, Oklahoma Gas Shales, Oklahoma City,References[ Arthur, J. 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Dallas TexasThermal MaturityTOC51/TocAm皿 mahre to any o中國(guó)煤化工CNMHGtance equvalent calaladed iom Rock-Eval TmaY vaShale gas plays geochemical data summary (Jarvie, 2008)61 No. 3 2009 Chre Petroleum ExploratronHarding- Sundance 1 CampbellHARDING COMPAN0.5mmPhotomicrograph of Barnett Shale laminated quartz siltstone( Harding Company, 2004)Appendix 3Harding 2 Dearing-RogersSchmidtY國(guó)煤化工MHGPhotomicrograph of Bamett Shale quartz sponge spicules(Harding Company, 2004)中國(guó)石油勘探x09年第3期62Appendix 4Shale CompositionAverage Clay: 38%Average Quartz: 36%ass。2Shale mineral composition(Jarvie, 2008)Gas shale logHigh to very high gamma rayactivityHigh resistivity到· High nuclear and sonic·LowPas shaleHH T-moTYH中國(guó)煤化工CNMHGTypical wireline log curves for gas shale( Ratchford, 2007)63 No. 3 2009 China Petroleum Exploration\\appendix 6DEPOSITIONAL MODELS OF RECENTSOURCE ROCK DEVELOPMENTOXYGEN MINIMNTINENTALWALVISLLAYINOTAN SHELPWELLING+自▲sNTHERMAL STAGNATIONOPEN MARINEBASINSCAAACO TRENCHHAUSTATIC STAINTRACRATOK看ANK6 SEMWATUA #### FRESH WATER ANOXIC ZoNE〓MnopVARIOUS TECTONIC SETTINGS FORSOURCE ROCK DEVELOPMENTSLOWLY SUBSIOING INTRACRATONICGEOSYNCLINAL BASINPARIS BASIN-.UASSICUPPER SEVON IAASINCoMPRESSIL CONTINENTAL飄 SIDING CONTINENTAL品RNWITH RELIEFN ZONECALIF。RNIA· MIOCENEAOMENERETACEOUSLe為 TONIC G典AENsNORTH SEA.UPPER JURASSICE VALLEY…L. TERTIARSOURCE角ocKs齜社"!TURBIOITES中國(guó)煤化工CNMHGRecent depositional and tectonic models for source rock deposition(eeken, 2007)中國(guó)石油勒探29年第3期64