China organic-rich shale geologic features and special shale gas production issues

Journal of Rock Mechanics and Geotechnical Engineering 6(2014)196-207Contents lists available at Science DirectJournal of rock mechanics andGeotechnical EngineeringCSRMEjournalhomepagewww.rockgeotech.orgFull length articleChina organic-rich shale geologic features and special shale gasCross Markproduction issuesYiwen Jua,b, Guochang Wang,bHongling Bu, b, Qingguang Li, b, Zhifeng Yan a, ba Key laboratory of Computational Geodynamics, Chinese Academy of sciences, Beijing 100049, Chinab College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, ChinaARTICLE INFOABSTRACTArticle history:The depositional environment of organic-rich shale and the related tectonic evolution in China are ratherReceived 26 February 2014different from those in North America. In China, organic-rich shale is not only deposited in marineReceived in revised formenvironment but also in non-marine environment: marine-continental transitional environment and10 March 2014cepted 15 March 2014lacustrine environment. Through analyzing large amount of outcrops and well cores, the geologic feaAvailable online 12 April 2014tures of organic-rich shale, including mineral composition, organic matter richness and type, and lithology stratigraphy, were analyzed, indicating very special characterMeanwhile. the morecomplex and active tectonic movements in China lead to strong deformation and erosion of organic-richshale, well-development of fractures and faults, and higher thermal maturity and serious heterogeneity.Co-existence of shale gas, tight sand gas, and coal bed methane( CBM) proposes a new topic: whether itOrganic mattduction issues of shale gas in China were discussed with suggestio. geologic features, the primary pro-is possible to Co-produce these gases to reduce cost BasedProductiono 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B V. All rights reserved1. Introductionrecoverable shale gas reserve is up to 25. x 102m in the landarea of China(Zhang et al., 2012a)Organic-rich shale, including mudstone and shale, was Organic-rich shale is not only deposited in marine environment,onventionally considered as source rock of hydrocarbon in sedi- but also in non-marine environment: marine-continental transi-mentary basins. Even though geologists observed natural gas in tional environment and continental environment(mostly lacus-organic-rich shale long ago(e.g Devonian Dunkirk shale in the trine facies) in China(Zhang et al., 2008: Zou et al., 2011). DistinctAppalachian basin in 1982 in USA and well Wei5 in Sichuan basin in from North America, marine organic-rich shale contains only 1/3 of1966 in China), the extremely low permeability(nano-level)in all recoverable shale gas resource and about 2 /3 shale gas was alsomatrix makes it hard to produce economical oil and gas flow to the generated and stored in marine-continental transitional facies andwell borehole (Wang and Carr, 2012). Over the past decade, continental facies (Zhang et al, 2012a) The marine shale gas resdraulic fracturing, and improved integration of geosciences and Yangtze platform and Tarim basin, while the continental andengineering, shale gas production has been increased rapidly in marine-continental transitional shale reservoirs were distributedNorth America(EIA, 2012). Opportunities for increased shale gas in Mesozoic and early Cenozoic formations of basins in North Chinaproduction appear to be global As investigated by Ministry of Land plate, basins in Northwest China and Sichuan basin. The differentand Resources of Peoples Republic of China in 2012, the types of depositional environments strongly affect the lithologystratigraphy, mineral composition, and organic matter type andorganic-rich shale spatial distribution. It is more difficult to produceesponding author. Tel :+86 1381000282shale gas from non-marine shale because of the higher clay content,uyw0300163.com(y.Ju)esponsibility of Institute of Rock and Soil Mechanics, Chinesehigher ratio of free to adsorbed gas, more interlayers and moreAcademyserious heterogeneity of shale gas reservoirs. As for the marineshale, even thoughAmerica. the中国煤化工 ncreases the difficulties to identifyProduction and hosting by elsevier2011: Cai et al. 20lCNMH Gn China (u et ald Liu, 2013: Zhang1674-7755 2014 Institute of Rock and Soil Mechanics, Chinese Academy ofet al. 2013a)Sciences. Production and hosting by Elsevier B.V. All rights reserved.In addition, water shortage, as a serious problem in many shaleY Ju et al. Journal of Rock Mechanics and Geotechnical Engineering 6(2014)196-207fracturing fluid system(Hu and Xu, 2013). Severely undulating primarily in the shelf of carbonate platform. Qiongzhusi shale ofsurface, pore development of infrastructure(e.g. roads ), and lack of Lower Cambrian, Wufeng shale of Upper Ordovician, and Longmaxigas pipelines increase the difficulties to produce shale gas in China. shale of Lower Silurian are the most promising shale gas reservoirsIt is significant to understand the geologic characteristics of in South China(table 1). The average thickness of Qiongzhusi shaleorganic-rich shale, their effects on shale gas production, and the is approximately 100 m, covering an area of 30 x 10-50 x 10kmspecial production problems of shale gas in China. Therefore, in this(Zou et al., 2011). The Wufeng-Longmaxi shale, covering most ofpaper, we will analyze the primary features of shale gas reservoirs, the Yangtze area, possesses the thickness up to 120 m. Severalincluding the spatial distribution, depositional environments, horizontal wells targeting Qiongzhusi and Wufeng-Longmaximineral composition, organic matter type, richness, and matura- shales have high initial production rate of shale gas. For example,tion. The special challenges of horizontal well and hydraulic frthe horizontal well Yang201-H2 is up to 43 x 10" m per day at theturing are discussed with suggestionsbeginning In Tarim basin, Yuertusi shale and Saergan shale are thepotential shale gas plays(Table 1). The primary characteristics of2. The major organic-rich shale in Chinaorganic-rich shale in China are listed in Table 1, including thickness,total organic carbon(ToC)content, kerogen reflection(Ro), organicReported by Oil & Gas Survey China Geological Survey, China matter (OM)type, distribution area, and depositional environment.has drilled 129 wells related to shale gas from 2009 to 2012During late Paleozoic, the development of organic-rich shale inincluding 46 vertical investigation wells, 55 vertical exploratory North China plate became more important(Fig. 1). For example,lls, and 28 horizontal assessment wells. the production of shale the coal-bearing organic-rich shale in Benxi group and Taiyuangas is about 0.25 x 102-0. x 10 2m in 2012 and is up to over group of Carboniferous and Shanxi group of Permian were2 x 102m in 2013. These shale gas wells, conventional wells deposited in the whole North China plate, and were primarilyenetrating organic-rich shale and a great number of outcrops preserved in Ordos basin, Qinshui basin, and southern Northprovide the basic information to investigate the basic properties of China plate(Fig. 1). Their depositional environment has beenorganic-rich shale and their distribution( Fig. 1)interpreted as marine-continental transitional facies. The total%a Organic-rich shale deposited before Pre-Cambrian was pre- thickness of the three organic-rich shales ranges from 30 m todominantly metamorphosed, except the doushantuo shale in up 180 m in the Ordos basin. Another marine-continental transier and middle Yangtze area(table 1 ). Organic-rich shales of early tional organic-rich shale, Longtan shale of middle Permian, isPaleozoic were preserved in Yangtze area and Tarim basin( Fig. 1), widely distributed in Yangtze area. The Junggar basin developedand all of these shales were deposited in marine facies(Table 1), three kinds of organic-rich shales during late Paleozoic, including人Sedimentary Basinlllll Unmetamorphozed Paleozoic Bedtozoic blockMesozoic Organic Mudrock中国煤化工Late Paleozoic Organic MudrockEarly PaleoCNMHGFig. 1. The distribution of major organic-rich shale in the land area of ChinaY Ju et al. Journal of Rock Mechanics and Geotechnical Engineering 6(2014)196-207Tableeristics of organic-rich shale in ChinaSystem period Organic-richAge code ThicknessTOC content RoDistribution areahale formationand welleogene10-4000.8-16Bohai gulf basin4-4.5I-II5-23unggar basinLF,866banging50-35006-35unggar basinJunggar basin80-60012-3.6LF,δ,6-1.2dos basinLF,86HuangshanjieTrh10-300.6-2.8Tarim basinTaliqikeT3t06-2.8Tarim basin0.41-10.0856-1.3120-5000.1-121.3-4West upper and lowerMCtF. 8angtzemengcheng50-3000.47-210.54-14110-500.5-36-3.4MCTF0.5-36.80.6-34North ChinaMCTF0.5-250.6-34ⅢⅢ--LNorth China plaACTF0.17-26.76MCTEDevonianLuofu600-11130.53-1299-203Longmaxi0.41-8.281.5-3.6gtze areaMF.666an0-250031-751141-3.2Lower Yangtze and south2023Ordos basin0.42-60.61-46512-4.6Tarim basin031.28-52Upper and middle Yangtze,Yuertusi0-2000.5-14.212-5Tarim basinDoushantuo10-2330.58-122-4.6Upper and middle Yangtzeote: Most data of thickness, TOC content, and Ro are modified from Wang et al. (2008), Zou et al. (2011) and wad Carr(2012): I-II means I and Il, while 1, Il means I isdominant and ll is secondary: in the last column, the relevant depositional environments include marine facies(MF), marine-continental transitional facies(MCTF), andlacustrine facies(LF): 8 indicates that only parametric shale wells, mostly shallow, are drilled; 00 indicates exploratory wells are drilled and 808 means production wells aredrilled and are producing shale gas.marine-continental transitional Dishuiquan shale with thickness fundamental ideas: preservation of organic matters as the mainof 120-300 m, lacustrine Fengcheng shale with thickness of 50- factor(Demaison and Moore, 1980; Ettensohn and Barron, 1981)300 m, and lacustrine Xiazijie shale(Table 1). Two marine shales, and production of organic matters( Pedersen and Calvert, 1990). ToLuofu shale and datang shale, were mainly deposited during date, most depositional models for organic-rich shale (black shalemiddle Devonian and early Carboniferthern upper combine both preservation and productivity of organic matters.meanwhile especially for the shale gas reservoirs, the functions ofNo marine organic-rich shale was deposited in the land area of sediment settling and dilution were emphasized. In fact, depositionChina during Mesozoic. Another typical feature is that rift basins in and accumulation of organic-rich shale are a complex procesNortheast China generally developed extremely thick organic-rich controlled by the interaction of terrigenous sediment settling rateshale in lacustrine facies, which is rather distinct from marine sediment dilution, organic matter productivity, and organic matterorganic-rich shale in North America. For example, the Shahejie preservation and decomposition(Sageman et al., 2003: Arthur andshale in Bohai Gulf basin and Qing I shale in Songliao basin are quite Sageman, 2005: Aplin and Macquaker, 2011; Wang and Carr, 2013)thick, but the organic-rich zones usually cover a relatively smallIn Fig. 2, Wang and Carr(2013) summarized three controllingarea in the deep fault blocks In the junggar basin and Tarim basin, factors on the deposition of marine organic-rich shale in forelandorganic-rich shale typically co-existed with coals and fine shaly basin: sediment dilution, organic matter productivity, and preser-sandstone, such as the Sangonghe shale, Badaowan shale, and vation. Even though this model was developed initially for marineXishanyao shale of Jurassic and Taliqike shale and huangshanjie shale in foreland basin, the fundamental ideas also work for all theshale of Triassic (Table 1 and Fig. 1). This kind of organic-rich shale other depositional environments. Of course, the contribution andis primarily deposited in the deep depressions of the basins. Finally effects of each factor could be different in marine and continentalbut most importantly, in the stable blocks( Sichuan basin and Ordos environments. The size and spatial distribution of water body andbasin), two organic-rich shales, Ziliujing shale and Chang7 shale, the distance of basin center to sediment source are very distincthave produced shale gas with gas liquids, showing good perspec- between open ocean, protected sea, large lack within craton, andtives as shale gas playsmall rift lack basin. Therefore the effects of sediment dilutionorganic matter productivity, and preservation vary in different3. Primary geologic features of organic-rich shale in Chinaedimentary settienentlv form different geologicfeatures of organic中国煤化工3. 1. Depositional model of organic-rich shaledeposited in the larCNMHGIC-rich shale wasspecially the shelfe When organic-rich shale was studied as source rock, the organic of carbonate platform(Fig. 3). The local depressions around thehess observed in organic-rich shale has been explained by two shelf were the preferred areas for the deposition of QiongzhusiIN-SITU BIOGENIC DETRITUSTERRIGENOUS CLASTICSediments DilutionIN-SITU ORGANIC MATTER-BRRIGENOUS ORGANIC MATTEROrganic Matter ProductivityDECOMPOSITIONSEDIMENTS BURIAL DEGREEOrganic matter PreservationDiSTAL APROXIMALFig. 2. Three controlling factors and their contribution to the deposition of organic-rich shale(modified after Wang and Carr(2013)). This conceptual cross-section was perpendicular to shoreline of foreland basin or lake basinhale and Wufeng-Longmaxi shale( Figs. 3 and 4) Distinct from the thickness of single layer is very thin but the amount of layers isNorth America, there existed several local depressions in Yangtze large. The frequent alternation of organic-rich shale thin limeplatform due to the differential subsidence and uplift. Therefore, itcoal, gray shale, siltstone, and fine sandstone is the mostis more complex to identify the distribution of organic-rich shale. notable feature of transitional organic-rich shale(Fig. 8b). Thehe relatively small water body size in depression and rifted lack most organic-rich part is close to the coal for transitional shalebasin obviously limited the development of organic-rich shale, Two types of lack basins exist for depositing lacustrine organic-which was generally deposited in the center of lack basins(Figs. 5 rich shale: the depression lake basin and rift lake basin. The liand 6). As for lacustrine organic-rich shale, the dilution of sedi- thology stratigraphy in depression lake basin( Fig. 8c) is similarments is more serious in decreasing the content of organic matter. with the marine-continental transitional organic-rich shale, excepthe coal-bearing organic-rich shale of marine-continental transi- that the distribution area of organic- rich shale is smaller. However,tional facies is primarily deposited in littoral swap, including for the lacustrine deposited in rift lack basin, the lithology stra-Longtan shale in Yangtze area(ig. 7)and Benxi-Taiyuan-Shanxi tigraphy is rather different from all the other organic-rich shaleshale in North China plate(Table 1)(Fig. 8d), which is interbedded with gray shale, siltstone, andandstone3. 2. Comparison among marine, marine-continental transitional,Another important difference is the mineral composition andand lacustrine shaleorganic matter richness and type. To investigate the differencesamong three kinds of shales, we have collected nearly 60 sets ofThe depositional environments have a significant influence on data about mineral composition and organic matter richness andthe geologic features of organic-rich shale. Firstly, the lithology type from more than 2500 articles and theses (Tables 1 and 2)stratigraphy is quite different. The marine organic-rich shale Meanwhile, parts of the data in Huainan-Huaibei coal field andusually overlies limestone and underlies gray shale(low ToC)with northwestern Jiangxi Province were tested experimentally by usa few very fine siltstones. Meanwhile, thin limestone beds are Totally, 756 samples were used to analyze the features of mineralommon in marine organic-rich shale( Fig 8a). The most organic- composition of organic-rich shale, including 599 data for marinerich zone is typically located in the lower part of the shale for- organic-rich shale, 44 for transitional organic-rich shale, and 113mation. For the marine-continental transitional organic-rich shale, for lacustrine organic-rich shale(Table 2). In addition, nearly half ofXichang LeiboXiushan Zhangjiajie Xinhua XintianProtected Shallow Sea Basin,05Wuyi MountainKanatien Old LandWuling-Xuefeng UpliftDepression in Craton BasinTYHd basinUplift中国煤化工tBetCNMHGFig 3. The marine shale depositional environment in upper Yangtze area of Southwest China(Zhang et al, 2013b)Y Ju et al. Journal of Rock Mechanics and Geotechnical Engineering 6(2014)196-207人KunmingBathyl Basin主 Carbonate platformˇ Evaporite Basin∴∵, Neritic Shelf1 Cratozoic blockFig 4. The paleo-environment in early Cambrian (modified from Wang and Cai (2007))and the isopach map of Qiongzhusi shale in the yangtze area. the unit of isopach is in meter.the data were from outcrop samples, which may result in the un- feldspar) in marine organic-rich shale are more than these inderestimation of carbonate minerals and pyrite. Other basic infor- lacustrine organic-rich shale, and consequently the brittleness inmation about data location distribution and shale formations is dex is higher in marine organic-rich shale; and (3)the content ofled in table 2pyrite in marine organic-rich shale is higher than that in other twoAll the 756 data concerning mineral composition of organic-rich facies, especially the transitional facies, which possibly indicatesshale were projected into the ternary plot for analysis(Fig. 9a). the higher reduction index in marine facies In terms of the clayMore than 90% of the samples are located in the area of carbonate mineral content( Fig. 10), illite and mixed i/s (illite and smectite)arecontent less than 20%, and about 2% samples contain carbonate the primary clay minerals in marine and lacustrine organic-richminerals over 60% The average content of silica minerals in all the shale while mixed Is and kaolinite are dominant in marine-data is 46.6%, and 36.8% for clay minerals and 12.7% for carbonate continental transitional shale. In addition, the content of smectiteminerals. The comparison among the different depositional envi- is relatively high in lacustrine organic-rich shale(Fig. 10). The Tocronments( Fig. 9b-d)indicates that: (1)marine organic-rich shale content in lacustrine and transitional organic-rich shale is highercontains more carbonate minerals and limestone interlayers could than that in marine organic-rich shale in China(Table 1). Due to thee often observed;(2)silica minerals (including quartz and toc content reflecting the residual total organic matters in shaleAnaerobic zone H,S的ese(a) Depression basin50Anaerobic zone H,S(b)Rifted basin. 4中国煤化工Planktonic AnaeNappe DeltaAlluvial fan/MudstoCNMHGfan delta faciesdi iFig. 5. The depositional model of lacustrine organic-rich shale in China(after Zou et al. (2013)).Fig. 6. The isopach map of Triassic organic-rich shale in the Tarim basin(a) and the 4th member of Shahejia shale in the dongying depression( b). the data for isopach map ismodified from Zeng et al. (2013)(a) and Zhang et al. (2012b)(b). The unit of isopach is in meterthe higher thermal maturity in marine organic-rich shale may Qiongzhusi shale has been eroded in the south Yangtze area anddecrease the toc content more. But, we believe that higher Toc Southeast China (Figs. 4 and 11), and outcrops of Qiongzhusi shalecontent in non-marine organic-rich shale is a typical feature in are common around the sichuan basin. The erosion of LongtanChina. The types I and ll of kerogen are predominant for organic- shale is more serious in South China( Fig. 6). Therefore, as geologistsrich shale deposited in marine basin and rifted lake basin, while stressed on depositional model of organic-rich shale in Northtype lll of kerogen becomes more important in organic-rich shale America, geologists in China have to pay their attention to thedeposited in marine-continental transitional environment and structural features in potential shale gas playsdepression lake basin(Table 1)ontrast to erosion, the differential uplift also leads to the largof burial depth of organic shale in the del3.3. Organic-rich shale erosion by tectonic evolutionexample, the deepest Qiongzhusi shale is up to over 5000 m, whichis a big challenge for hydraulic fracturing. According to the experience in North America, the burial depth of 1500-3000 m isAs the depositional environments control the original geologic considered as a suitable target for shale gas reservoirs. The largefeatures of organic-rich shale(e.g. shale composition, organicburial depth not only increases the cost of drilling and the diffimatter,and distribution ) tectonic evolution is the following factor, culties of fracturing, but also improves the thermal maturity ofwhiches these original geologic features. This is extremely organic matterinportant in China. Compared to North America, China has sufferedfrom complex and active tectonic movements from Pre-Cambrian.sided together except the orogenic belt in North America, such as 3. 4. Detachment structure and deformation of organic-rich shalethe Appalachian basin. However, the basements of China wereAccording td v凵中国煤化工 ps and well corescomposed of several discrete land masse1)the fracturesdifferential uplift seriously. Many organic-rich shales, especially the cially the marinCNMHGIIC-TIch shale, espee area Fig. 12). ThePaleozoic organic-rich shale in Yangtze area and Southeast Chmultiple stages of tectonic movements have resulted in tihave been explored into the air or eroded totally. For example, the fractures crossing with each other ( Fig. 11a-c). The shale has beenY Ju et al. Journal of Rock Mechanics and Geotechnical Engineering 6(2014)196-207人E Carbonate PlatformDeep Water Carbonate Basinha Fan Deltaa. Littoral and Shallow Sea中 Source land-1Fig. 7. The paleo-environment in early Cambrian(modified from Wang and Cai(2007))and the isopach map of Longtan shale in the Yangtze area. The unit of isopach is in meter.broken into many small parts, which is not good news for hy- evolution, the in-situ stress of shale formation is relatively high indraulic fracturing and shale gas preservation. Most of these the area with large burial depth and close to the orogenic belt.fractures have been filled with calcites primarily and quartz Meanwhile, due to the well-developed faults and variations of faultsecondarily. These fractures are predominantly related to reverse direction, it is more difficult to evaluate the in-situ strefaults and thrust faults (Fig. 11). Detachment structure was Yangtze area than that in North America and North China plate andcommon in organic-rich shale and also caused strong deforma- basins in the west chination of organic-rich shale, which is the soft rock undergroundcompared with limestone and sandstone. In coal-bearing organic- 3.6. Co-existence of shale gas, tight sand gas, and coal bed methanerich shale, besides tectonic deformation, dehydration of shaledue to exploration into the surface directly, also formed manyIn the non-marine organic-rich shale, especially the coalsitional organic-rich shale from Huainan-Huaibei coal fields, thin coal, siltstone, and fine sandstone Organic-rich shale and coalshrink fractures were well-developed (Fig. 13). Large portion of are the source rock and gas reservoir, while siltstone and finethese fracturre filled with organic matters while others sandstone store parts of the gas migrating out from organic-richwere open or filled with calciteshale and coal (Fig. 8b and c). therefore, provided the reservoirwith a good accumulation condition and a good preservation, shale3.5. Thermal maturity and in-situ stress of organic-rich shalegas, tight sand gas, and coal bed methane(CBM)co-exist with eachother in many coal-bearing strata. The coal-bearing strata areAnother effect of complex tectonic evolution is that the variation widely distributed in most sedimentary basins in China. With theof thermal maturity of organic matter is large for different shale in wide distribution of coal (accounting for about 80% of energydifferent basins, even the same shales in different structural units in consumption in China), this kind of lithology stratigraphy is veryChina. Especially for the marine organic-rich shale in Yangtze area, significant in China. According to the investigation by Ministry ofRo varies from 1.5% to 5.0%(Table 1). In most area, the ro of marine Land and resources of People' s Republic of China in 2012, the shaleorganic-rich shale is over 2.5%, which is much higher than that in gas in coal-bearing strata could be up to half of total recoverableNorth America and lacustrine organic-rich shale in China. However, shale gas in Chinane shale gas ic ahnut 2/3). Due to thefor the lacustrine organic-rich shale, the thermal maturity is rela- relatively small th中国煤化工 and the frequenttively low and, for a few organic-rich shales, the highest Ro is just alternation of orgarabove gas window (e.g. Chang7 shale in Ordos ) In fact, shale oil or it is non-commercCNMH Gnd hine sandstonese unconventionalgas liquid in these low maturity shales, including Chang 7, Shahejie, gases individually. The joint development of shale gas and CBM orngmore important. Affected by the tectonic shale gas and tight sand gas or all together could be a goodStrata_Depth Lithology Sys Fm.(m)/ Lithology Sys. Fm.L(m).Sys. Fm.(mStrata Dept Lithology Sys Fm/(m) Lithology2120160268027021601802720220027402202760224027802402280Fig 8. Lithology section of organic-rich shale formations in wells and outcrops. (a) Marine shale(modified from Liang et al. (2012)).(b)Marine-continental transitional shalemodified from Gong et al. (2013).(c) Lacustrine shale in depression basin (modified from Ma(2013).(d) Lacustrine shale in rift basin(modified from Liu et al. (2012)opportunity to effectively develop and utilize these unconventional deposited in marine environments. Meanwhile the geologicgases in coal-bearing stratastructure is relatively stable in North America. However, the basement of China is composed of several discrete paleo-land masses4. Special issues of shale gas production in Chinaand consequently differential uplift and subsidence are seriousShale gas is unprecedented and inspiring for people especially Qiongzhusi shale and Longmaxi shale, were developed in earlyfor China such a country with a higher population, while there are Paleozoic, which suffered from multiple tectonic movements, suchmany special issues existed inas Indosinian movement, Yanshan movement, Himalayanorogenyand so on (u et al., 2005). The differences among different struc-4.1. Complex tectonic evolutiontural units in Yangtze area are obvious, including burial depth,erosion and deformation faults and fractures in-situ stress. andChina has experienced complex tectonic evolution compared to thermal maturity. The strong heterogeneity of organic-rich shale inNorth America. The organic-rich shale in North America is mainly China related to complex tectonic evolution has markedlydistributed in the early Paleozoic and Mesozoic and predominantly increased the difficulties of shale gas exploration. Furthermore, allTable 2The basic information of coldata concerning mineral composition of potential shale gas reservoirs.Depositional faciesData sourceData locationTransitionaOutcropWellYangtzeOrdos basinBohai gulf basinOthers113402中国煤化工TotalOrganic-rich shale formationYHiCNMHGhusiDalongBenxi-Taiyuan-Shanxi756129Y Ju et al. Journal of Rock Mechanics and Geotechnical Engineering 6(2014)196-207Pyrite(%)o Well Datao Well Data246802462468Carbonate Mi>Clay Minera Carbonate Minet40(c)Pyrite(%)Well DataWell Datao Outcrop Data80246pW02Clay Minera( CarbonateClay MinFig 9. Mineral composition features of organic-rich shale deposited in different environments in China. (a) All data together. (b) Marine organic-rich shale. (c) Marine-continentaltransitional organic-rich shale.(d) Lacustrine organic-rich shale.hese features are not beneficial to the effective design of horizontal very higher clay contents, which are water-sensitive especially forwell and hydraulic fracturing, and will increase the associated cost. kaolinite and smectite, which is detrimental to hydro-fracture. tosolve these issues, CO2 is considered as a fracturing fluid during the4.2. fracturing of non-marine shalereservoir stimulation. In addition, thousands of oil and gas tech-nology service companies in USA can provide professional designTo date, most experiences of hydraulic fracturing of organic-rich and suggestion concerning the local issues of hydraulic fracturingshale are from marine shale in North America. It is questionable to However, professional oil and gas technology enterare lackeduse them directly to the stimulation of organic-rich shale in China, in China, which also increases the risk and cost of stimulationespecially the non-marine shale. To non-marine shale, there have4.3. Joint development of multiple unconventional gases60China is the first coal production country in the world and thecoal resource accounts for 37% worldwide, the ordos basin isknown as a large coal-bearing basin, which possesses greater than500 billion tons of coal resource. In the coal-bearing strata, organirich shale is typically interlayered with coal and fine sandstone,especially in marine-continental transitional facies and lacustrineTransitionalfacies in depression lake basin. In coal mining fields, the organ言20existence of shale gas and CBM is common in the coal-bearingstrata(Chen et al, 2011), such as the Longtan group in Yangtzeregion(Fig. 7) and Benxi-Taiyuan -Shanxi group in North ChinaLacustrineplate. In addition, the thin sandstone will store gases migrating outfrom coal and shale gas as the fine sandstone inteand organic-richof organic-rich mu中国煤化工ne, it is non-ommercial to producKaolinite Chlorite Smectite Mixed I/Sproduction of theCNMHGis a good idea toFig 10. The highest, average, and lowest contents of clay minerals in different depo-efficiency. Therefore, combinsitional environments in Chinaresearch and development is the nice choice for shale gas and CBMY Ju et al. Journal of Rock Mechanics and Geotechnical Engineering 6(2014)196-207PI-ZFront Detachment Fault-Fold Zone Transition ZoneCompressional Fault Block-Basal Fault-Fold ZoneFig. 11. Structural profile of eastern Sichuan basin and western Hubei-Hunan area(modified from Ma et al. (2012)).11234D6)o(c) Compression fractureFig 12. Well-developed fractures observed in the well cores of marine organic-rich shale in Yangtze area, China. (a)Well Keyel(modified from Xie et al. (2013)). (b)Well Changxin1d from Chen et al. (2013).(c)Well Yuyel (modified from Long et al. (2012)).(d) Well Cenye 1(modified from Zhao(2013)).ganic MatterQuartz Filled Fracture中国煤化工(d)CNMHGFig 13. Thin section images of late Paleozoic coal-bearing shale in coal mining area of southeastern North China plate. (a) Sample HB-LH-2(PP, 100x);(b)Sample HB-LH-2(CP,100x ): (c)Sample HB-LL-1(PP, 100x ) and (d) HB-LL-1(CP, 100x). CP: crossed polarized light; PP: plane polarized lightY Ju et al. Journal of Rock Mechanics and Geotechnical Engineering 6(2014)196-207even other natural gas in some sedimentary environment. These Therefore, besides discussing the depositional model of organictechnologies can be used as a long-term viewrich shale in the three environments tectonic evolution is alsoa very important topic for shale gas in China. Furthermore, non-4.4. Water issuemarine shale, especially the coal-bearing organic-rich shale iswidely developed in China. Interlayered with coal and fiHydraulic fracture is used in the process of extraction of shale sandstone the co-existence of shale gas, tight sand gas, and CBMgas in China, while there are two issues on water. Firstly, the water has been observed in Ordos basin, Sichuan basin, and middle-in shortage. According to the public data, segregated completion lower Yangtze area. It is possible to co-produce these gases toand clustering fracturing in the horizontal shale gas wells need reduce cost. More geologic analysis and discussion should bemore than 10,000 tons of water per well. The population in China completed to support the shale gas development in China. Theaccounts for 24% of the world population, but the water only ac- special geologic properties of organic-rich shale and other relatedcounts for 6%. Meanwhile, the uneven distribution of water re- problems(such as undulating surface condition, water shortage,sources further worsens the water shortage. Thus, it is a huge lack of pipeline, and technology service companies)cause morechallenge for shale gas development in China. For example, the difficulties to produce shale gas in China. For example, waterwater shortage in Tarim basin has delayed the development of shale shortage, as a serious problem in many shale gas basins in China,gas, while in Sichuan basin, even though more water resources, it is should be overcome through developing new fracturing fluidalso urgent for water supply owing to the dense population. As a system Severely undulating surface, pore development of infraserious problem in many shale gas basins in China, water shortage structure(e.g. roads ) and lack of gas pipelines increase the dif-should be a challenge that we must overcome through developing ficulties to produce shale gas in Chinanew fracturing fluid system( Hu and Xu, 2013). Secondly, the waterpollution will lead to more serious issues close to the headwaters, Conflict of interestsuch as Sichuan basin The most active shale gas events are going onin Sichuan basin polluted water from fracturflow down toWe wish to confirm that there are no known conflicts of interestthe east China where the elevation is lower, which will lead to large associated with this publication and there has been no significantea pollution of water resourcesfinancial support for this work that could have influenced itsoutcome4.5. Surface condition and infrastructureThe shale gas wells in USa are usually located in the plaAcknowledgmentsvoiding the mountain areas. However, in China, the mostperspective shale gas plays are in upper Yangtze area, such asThis work was financially supported by the National NaturalSichuan basin and eastern Chongqing, where the surface elevationScience Foundation of China( grant Nos. 41372213, 41030422 )andvaries from 1500 m to 3000 m. The relative elevation is up to Strategic Priority Research Program of the Chinese Academy of1000 m. It is a tough task to transport the huge equipment for Sciences(Grant No. XDA05030100)drilling and fracturing to the well sites. The infrastructures, such ashigh way and road, are poorly developed due to the undulating Referencessurface and local underdeveloped economy. The oil and gas com-panies have to invest in developing infrastructures, along with Aplin AC, Macquaker JHS Mudstone diversity: origin and implications for sourceseal, and reservoir properties in petroleum systems. AAPG Bulletin 2011: 95(12)dealing with water shortage and environmental protection(Zouet al., 2012). In addition, the transportation of produced shale gas Arthur MA, Sageman BB Sea-level control on source-rock development: perspis also a big issue in China. Different from USA, the gas pipelines areves from the Holocene black Sea, the Mid-Cretaceous western interior basin oforth America, and the late Devonian Appalachian basin. In: Harris NB.nadequate and constructed very slowly. Until July 2013, China justPradier B, editors. The deposition of organic carbon-rich sediments: mebegan to build the first shale gas pipeline from the shale gas wellN201-H1. More investments are necessary for China to develop9.SEPM Special Publication No 82.Cai ZR, xia B. Wan ZE The characteristics of later tectonic activities andinfluence on the preservation of the Paleozoic shale gas in Wuhu area, LYangtze Platform. Journal of China Coal Society 2013: 38(5): 85. ConclusionsChinese).Chen SB. Zhu YM, Li W. Luo Y, Wang HM, Zhong HQ, Geologic optimization of shalegas and coal bed methane combined research develop in Yangtze, ChinaChina is investing huge funding and issuing preferential polJournal of Liaoning Technical University( Natural Science)2011: 30(5): 672-6es to encourage and improve the development of shale gas Chen Wl. Zhou W, Luo P, Deng HC, Li Q, Shan R, Qi MH. Analysis of the sindustry, dealing with the huge consumption of energy. However,the special geologic features of organic-rich shale affected bySichuan basin, China. Acta Petrological Sinica 2013: 29(3): 1073-86(indepositional environments and tectonic evolution have led to Demaison G Moore GT. Anoxic environments and oil source bed genesis. Organicnew challenges. It is the first step to understand these geologicEnergy Information Administration(ElA). Annual energy outlook 2012 with pro-characteristics and then to find the solution. Based on largections to 2035. Washington DC, USA: EIA; 2012.amount of data tested by ourselves and collected from published Ettensohn F. Barron L. Tectono-climatic model for origin of Devarticles and theses, the geologic features of organic-rich shale,black gas shales of east-central United States. AAIFang LZ, Ju YW, Wang GC, Bu HL. Composition and gas-filled pore characteristics ofincluding mineral composition, organic matter richness and typePermian organic shale in the southwest depression of Fujian, Cathaysia landand lithology stratigraphy, were analyzed in marine, marine-mass. 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Journal of Southwest Petroleum University(Science and Tech-ology)2012: 34(6): 27-37(in Chinese)Pedersen TF, Calvert SE. Anoxia vs. productivity: what controls the formation oDr. Yiwen Ju, is a professor and doctoral student supervisororganic-carbon-rich sediments and sedimentary rocks? AAPG Bulletin 1990: 74in University of Chinese Academy of Sciences(UCAS), and isa senior research scholar of Virginia Polytechnic InstituteSageman BB, Murphy AE, Werne JP, VerStraeten CA, Hollander DI, Lyons Tw. A taleand State University. He is the academic leader of unconof shales: the relative roles of production, decomposition, and dilution in theventional gas research in UCAS. He managed over 20 proaccumulation of organic-rich strata, middle-upper Devonian, Appalachian bajects as Pl, which are funded by National Natural Sciencn Chemical Geology 2003: 195: 229-73nd techno-Wang QC, Yan DT, Li SI. Tectonic-environmental model of the lower Silurian high-gy Projects of China, National Basic Research Program ofquality hydrocarbon source rocks from South China. Acta Geologica Sinichina(973 Program), Strategic Priority Research Progra2008:82(3):289-97( in Chinese).the Chinese academy of Sciences, Natural Science FoundWang G, Carr TR, Organic-rich Marcellus shale lithofacies modeling and distrition of Beijing and China Postdoctoral Science Foundation.prediction: a case study from Marcellus shale in the Appalachian basin. Com- Reservoirs. he was presented seven awards including Natural Science Award and sciputers Geosciences 2012: 49: 151-63nce and Technology Progress Award. He also has much experience concerning interCai LG Phanerozoic tectonic evolution of South China. ACTA Geologica national exchanges and cooperation studies with colleges and universities or scientifiSinica 2007: 81(8): 1025-40 (in Chinese).research institution of the United States, Australia, and Germany. He was theXie C, Zhang JC, Li YX, Wang XH. Characteristics and gas content of the lower proposer and one of executive chairmXiangshan Science Conferences with theCambrian dark shale in Well Yuke 1, southeast Chongqing Oil Gas Geologyasic Problems of Deep Coal Mine Gas Disaster and Coal bed Methane2013: 1: 11-5(in Chinese).evelopment in 2012 and The Frontier Scienceg WT, Ding WL Zhang JC, Li C, Xu CC, Jiu K, Wu LM. Analysis of geologic controls Accumulation or Metallogenesis in 2013, a session chair( Shale Plays of China)at theon shale gas accumulation in northwest China. Geologic Science Technology:013 AAPG Annual Convention and Exhibition a member of a counnese sul4): 139-50(in ChinesSociety for Soft Rock Engineering Deep Disaster Control, committZhang DW, Li YX, Zhang JC, Qiao Dw, Jiang WL, Zhang JF. National survey arhe associate editor-in-chief of"International Journal of Coal Science Mining Engineer-Zhang HQ, Xu XS, Liu W, Men YP. Late Ordovician-early Silurian sedimentary facies ing", editorial board member of "China Coalbed Methane"and executive member of theand palaeogeographic evolution and its bearings on the black shales in the council of Scientific Chinese中国煤化工CNMHG