Spatial coupling relationships of gas hydrate formation in the Tibetan Plateau

http://www.scar.ac.cnSciences in Cold and Arid Regions2013,5(6):0691-0697DOI:10.3724/SP.J.1226.2013.00691Spatial coupling relationships of gas hydrate formation inthe Tibetan plateauQiang Zhou, WanLun Li, WeiTao Chen, Yong Jiang Wang1. China Aero Geophysical Survey& Remote Sensing Center for Land and Resources, Beijing 100083, China2. China Geological Library, Beijing 100083, China3. China University of Geosciences, Wuhan, Hubei 430074, china*Correspondence to: Dr Qiang Zhou, Research Associate of China Aero Geophysical Survey remote Sensing CenterforLandandResourcesNo.31,XueyuanRoadBeijing100083,China.E-mail:zhouqqg@163.comReceived: November 12, 2012 Accepted: March 3, 2013ABSTRACTAt present, gas hydrates are known to occur in continental high latitude permafrost regions and deep sea sediments. Formiddle latitude permafrost regions of the Tibetan Plateau, further research is required to ascertain its potential developmentof gas hydrates. This paper reviewed pertinent literature on gas hydrates in the Tibetan Plateau. Both geological and geographical data are synthesized to reveal the relationship between gas hydrate formation and petroleum geological evo-lution, Plateau uplift, formation of permafrost, and glacial processes. Previous studies indicate that numerous residualbasins in the Plateau have been formed by original sedimentary basins accompanied by rapid uplift of the Plateau. Extensive marine Mesozoic hydrocarbon source rocks in these basins could provide rich sources of materials formhydrates in permafrost. Primary hydrocarbon-generating period in the Plateau is from late Jurassic to early Cretaceous,hile secondary hydrocarbon generation, regionally or locally, occurs mainly in the Paleogene. Before rapid uplift of thePlateau, oil-gas reservoirs were continuously destroyed and assembled to form new reservoirs due to structural and thermaldynamics, forcing hydrocarbon migration. Since 3.4 Ma B P, the Plateau has undergone strong uplift and extensive glaciation, periglacier processes prevailed, hydrocarbon gas again migrated, and free gas beneath ice sheets within sedimentary materials interacted with water, generating gas hydrates which were finally preserved under a cap formedfrozen layers through rapid cooling in the Plateau. Taken as a whole, it can be safely concluded that there is great temporalnd spatial coupling relationships between evolution of the Tibetan Plateau and generation of gas hydratesKeywords: gas hydrates; petroleum geology; frozen earth and glacial; Plateau uplift; spatial coupling relationship Tibetan1 Introductionperiod of growth and development. The need for energywill be a huge challenge for this development. NaturalThe Tibetan Plateau, considered as the worlds roof, gas hydrate, a new source of next generation energy, hasattracts people from all over the word because of its been found in several oceans and a pilot project in a highunique climate, exquisite scenery and mystic qualities of latitude permafrost area of Canada(zhu, 2006), showingits inhabitants. The Plateau has also attracted attention great application potential. Although permafrost regionsdue to its extremely subtle geology, and rich endowment in the Tibetan Plateau lie at middle latitudes, some specof ores and energy resources which are posed for exca- ifications can be correlated with gas hydrates in highvation and developmentlatitude permafrost regions(Zhang and Xu, 2001)Due to construction and opening of the Qingzang Meanwhile, thertences of gaRailway, the Plateau will experience a new vigorous hydrates in theTYHa中国煤化). Chen et al.CNMHG692Qiang Zhou et al, 2013/Sciences in Cold and Arid Regions, 5(6): 0691-0697(2005)adopted a predictive method based on stable counting for 26% of the total in the Tibetan Plateauthermodynamic field, according to both thickness and Within three major Mesozoic hydrocarbon source bedsgeothermal gradients of the Plateau's frozen zone, and the proportions of hydrocarbon amounts generated bypredicted about 1.2x10-24x10 endowment of gas upper Triassic, Jurassic and lower Cretaceous are nearlyhydrates in the Tibetan Plateau. Recently, Lu et al.(2010) equivalent Mesozoic source beds in the Tibetan Plateauacquired experimental samples of gas hydrates through mainly produce gas, and the amount of oil including gasdrilling at the Muli perennial frozen region on the south condensate only account for 29.36% of the total quantityedge of Qilian Mountains. These activities have created of hydrocarbon generation, and the amount of oil generenthusiasm for the exploration of gas hydrates in this ated in the Qiangtang Basin account for 49% of the totalregion. However, with global climate change, the Tibet- quantity of oil generation. When secondary hydrocarbonbegin to thaw leadigeneration is considered, Mesozoic marine source bedsconditions in relation to preservation of gas hydrates, in the Qiangtang Basin are estimated to generate sec-thus inevitably releasing a great deal of gas hydrates. ondary hydrocarbons, in the amount of 924.28x10 tThe Tibetan Plateau, as a potential gigantic "carbon re- accounting for 9.31% of the total hydrocarbons generatserve, will certainly affect global climate as soon as the ed during the mesozoic in this basin(zhao et al., 2000b)ore of gas hydrate is explosively released. Therefore, In 1993, the China National Star Petroleum Corporationwhether for the sake of energy or environmental protec-(CNSPC) drilled the first petroleum discovery well attion, it is necessary to ascertain the distribution of gas Lunpola in northern Tibet. In 1999, the pilot productionhydrates on the Tibetan plateauwas successfully completed, thus ending the speculationThispaperhasperformedacomprehensiveanalysisthatTibetlackednaturaloilreserves(http://wwwof basic geology and petroleum geology, uplifted of the cngascn. com/up files/news/84306500 pdf)Plateau and formation of frozen earth, as well as glacialThese petroleum resources provide enough sourcemigration, and discussed the coupling relationship be- material to form gas hydrates, a prerequisite of existingtween petroleum geology of the Tibetan Plateau and gas gas hydrateshydrates both spatially and temporally. We conclude thatthe Tibetan Plateau has great potential for the develop- 2.2 spatial and temporal correlation between petro-ment of gas hydratesleum resource and gas hydrate2 Space-time correlation between formation of gasNumerous residual basins are preserved in the Tihydrate and petroleum resourcebetan Plateau(Zhao et al., 2000b), which are tectonicresidual basins formed by original sedimentary basins2.1 Petroleum resource on Tibetan plateauthrough late reworking following rapid and total uplift ofthe plateau. These residual basins after the plateausThe Tibetan Plateau, lying at the eastern segment of uplift of 4,000-5,000 m, guarantee the preservation ofthe Tethys petroliferous tectonic region, has the highest petroleum resources, an important factor controllingproduction of oil and gas in the world as well as the most formation of gas hydrates(Fu, 2005)abundant reserves, and has developed a series of relaThe Qiangtang Basin formed during the late Triassictively large, both in scale and sedimentary thickness, to late Jurassic, and the initial shape of which may haveMesozoic and Cenozoic petroliferous basins, including been preserved in the mid Cretaceous. This residual baoth groups of terrestrial and oceanic basins(zhao et al., sin has been subjected to two obvious reworking durin2000a). The period and distribution of hydrocarbon the late Yanshanian and Himalayan periods. Hydrocarsource rocks in the Tibetan petroliferous basins are simi- bon generation is closely related with the evolution ofar to those of central and eastern regions of the middle the basin. In this region, the double occurrence of hysegment of the Tethys. The major source rocks should be drocarbon generation, migration and accumulation ofJurassic to Cretaceous marine sediments related with large quantities of oil and gas, and eventually trapped asevolution of the Tethys (Wang et al., 2006). For instance, ores might be limited to the end of the Oligocene. also,main source rocks in the Qiangtang Basin are upper Trthe preservation period of petroleum might be after theic to upper Jurassic, while those in the Cuoqing Basin Miocene(Wang et al, 2001). All four major source bedsare lower Cretaceous. In addition, there are also hydro- namely T3x, J2b, J2x and J3s, have undergone hydrocarbon source rocks in the Biru, Changdu, and Kekexili carbon generation at least two or more times, amongbasins. According to a preliminary estimate, total amount which primary generation occurred in the late Jurassic toof hydrocarbon generated in source beds of upper early Cretaceous, almost simultaneous with regionalPaleozoic. Mesozoic and Cenozoic in the aforemenstructural deformation of the late Yanshanian periotioned basins is about 38, 1285x10%t. The amount of Hydrocarbon gas is mainly stored in anticline traps ofhydrocarbon generated by Mesozoic source beds in the Jurassic to Cretpe Secondarv hydrocarbon gen-Qiangtang Basin alone reaches to 9,930.92x10 t, ac- eration mainly中国煤化工ry, with localCNMHGQiang Zhou et al, 2013/Sciences in Cold and Arid Regions, 5(6): 0691-0697693or regional well-preserved petroleum resource generated formation of ever-frozen earth at about 0. 71 Ma B Pduring this period(zhao et al., 2000b). In the Qiangtang Free and difficult-to-preserve natural gas, can underBasin, numerous thrust-detached structures developed in conditions of low temperature and high pressure, bethe late Miocene, forming "duplicate structures with preserved in a cryospheric setting. Therefore, petrolepassive roof providing space for accumulation of oil um resources and gas hydrates in the Tibetan Plateaund gas. On the other hand, the Neotectonic movement has certain spatial and temporal correlations with eachsince the Tertiary formed stable lozenge terranes, which other. a preliminarily conclusion is that petroleum remainly show differential block uplift, are relatively sta- sources might reside below gas hydrates, and gas hyble within the blocks, and have little effect on the drates is dominated by a mixture of both light andpreservation of oil and gas. These Himalayan fault heavy hydrocarbonsblocks or anticlines might also form effective accumulation areas for oil and gas(Wang et al., 2001)3 Coupling relationship between formation of froThe Tibetan Plateau from the oligocene to Pliocenezen earth and preservation of gas hydrateunderwent strong rifting and volcanism, thus its tectoncS, magmatism and uplift of the Plateau are closely couThe Tibetan Plateau has been subjected to mo-pled. During the uplift process of the Tibetan Platetile-uplift and planation multiple times during the cengformed due to tectonic evolution, corresponding struc- Zoic, especially geological processes after the Plateautural traps became available for oil and gas to accumu- entered a frozen period. These tectonic movements arelate and become ores. Also, due to strong tectonic significant for both formation of frozen earth andle of uplift and incision was relatively preservation of gas hydrates. The Kun(lun)-Huang(he)large, destroying the preservation of oil and gas. Zhao movement period occurred in 1. 1-0.6 Ma B P. (late Earet al.(2000b)suggested that secondary petroleum mi- ly Pleistocene to early Middle Pleistocene), and is angration in the Qiangtang Basin served as both accumu- important stage of uplift during the formation of the tilation and destruction, dominated by accumulation, betan Plateau(Figure 1). After this movement, the Ti-with early generated oil and gas possibly being de- betan Plateau uplifted to an altitude above 3, 000 m. Thisstroyed. During the Early Yanshanian and Late Hima- uplift, coupled with an orbit transition called the"Middlelayan, regional magmatism was relatively strong, with Pleistocene Evolution"and global cooling, caused thelocal temperature increase that obviously promoted Plateau's mountains to enter into the cryosphere, form-thermal evolution of organic material, and destroyed ing the largest Quaternary glacier in the Tibetan Plateauearly generated petroleum reservoirs. During the pulse This glaciers equivalent to the maximum glacial perioduplift of the Plateau, both structural and thermal dynamic within the Qingzang glacier series at the Marine Isotopforces driving hydrocarbon migration destroyed early Stage(MIS)20-16 with a total area exceeding 50x10etroleum reservoirs to some extent but at the same time km"(about one quarter of the Plateau area). Glacial areagenerating new reservoirs. During the Qingzang move- at the maximum period incorporated the central andment of the Pliocene to Pleistocene, strong heat sources eastern mountainous districts, namely Tanggula, Amnepromoted organic materials within basin hydrocarbon Machin, Golok and Daocheng Haizi mountains, which issource rocks into a highly mature stage, however plenti- 18 times that of the modern glacier. Except for summer,ful light hydrocarbons are difficult to preserve due to stable snow cover on the plateau, along with thestructural destructioners large area, increasing surface reflectanceDuring the multi-pulse and rapid uplift of the Ti- strengthening of the cold high pressure above the Plateaubetan Plateau, especially from the holocene to the end in winter, has allowed further cooling of the Plateau(shiof the Pleistocene, the whole Plateau experienced the et al., 1998)source Aviolent summer monsoonPlateau entering into cryosphere后,km邮TTTYTTT3.5GM3.02.01.5M/B0.5Figure 1 Stepwise uplifting of the Tibetan Plateau since 3. 4MyH中国煤化工CNMHG694Qiang Zhou et al, 2013/Sciences in Cold and Arid Regions, 5(6): 0691-0697The Last Glacier Maximum(LGM)occurred at the of about 3, 500-4, 700 m, summer temperature at theend of the Late Pleistocene. The rapid uplift of the balance line is about -2 to-4C, and annual averagePlateau led to surface change from a warm, semi-arid temperature lies between-4 to -12C Supposing at thata large area of permafrost. During the Holocene, this 3, 500 m, surface a titude of the Tibetan Plateau waslarge scale ice age ended, the Plateau experienced con- below 0C. When annual average temperature dropstinual uplift to an altitude above 4,000 m, and the re- below -2.5C, Plateau permafrost is widely formedgion remained a periglacier environment due to its spe- especially in the western portion of the Plateau with relal altitude. During the early Holocene warming peatively less rainfall, higher relief and colder temperatures,od(10-8 ka B P ) after the cold and dry climate of the indicating that the Tibetan Plateau fully entered the crylast glacial period, the climate of the Plateau gradually osphere during Lgm(Shi et al., 1998)became warm and humid. The middle holocene relaThe temperature of LGM is about 7C below todaystive warming period ( 8-3 ka B P. is a climatic opti- temperature, so the area of permafrost should be relamum during a post glacier stage of the Plateau. The tively enlarged. The area of modern permafrost in theLate holocene cool period since 3 ka B P. with a ceTibetan Plateau is about 1.6x10 km, its peripheraler climate due to continuous uplift of the Plateau, is the boundary equivalent to annual average temperature of-2coldest stage during this period, and mountainous gladto-3oC. Inferred from modern annual average isotheriers on the Plateau generally advanced. Climatic insta- mals, the area where modern temperature is 3-4Cbility of the Megathermal in the Holocene is obvious, should have developed permafrost during LGM (lowerwith rapid cooling in both warm and warming periods than -3C. Thus, permafrost distribution during LGm(Shi et al., 1998)is roughly divided into: (1)north, incorporating most ofIn general, annual average temperature below -2C the Qaidam Basin, reaching to Qinghai Lake and thesuitable for discontinuous permafrost formation, while Gonghe Basin;(2)south, the upstream valley of Yar-nnual average temperature below -8C is suitable for lung Zangbo River; and (3)east, a significantly expandedcontinuous permafrost formation. For the Tibetan Plat- area(Figure 2). Thus, the area of permafrost in the Tieau in LGM, namely the MIs 16 stage(about 0.8 Ma betan Plateau was up to about 2. 2x10 km, almost 40BP), the glacier line of balance ranges between altitudes larger than today( Shi and Zheng, 1997)80°E90°E95°E00°E45°N45N40°N40N35°Nmim330oN- WIll Permafrost during LGM: 2.2x10-km'0180360540kmB Present permafrost in the plateau:1.6x10-km?30°N85°E90°E95°E00°EFigure 2 The extent of permafrost during the present and lgm in the Tibetan Plateau (shi et al., 1997)The rapid decrease of water supply for lakes and to increase salt content and salinity of lake water,cauponds in the Tibetan Plateau at the end of the Late ing an enrichmePleistocene, together with increasing evaporation, led The study on中国煤化工 dicated thCNMHGQiang Zhou et al, 2013/Sciences in Cold and Arid Regions, 5(6): 0691-0697695there were lacustrine deposits from fresh water between ice cover to the periglacial zone. Therefore, under sili35-3 ka B P, but it has gradually become salt lake and mar conditions, the periglacial zone of past or moderndeposited gypsum since 23 ka B P. Chen et al.(1990) glacial shields should have relatively more petroleumsuggested that most evaporite deposits in Qarham salt resources ( Jiang et al., 2002)lake of the Qaidam Basin began at about 24 ka B PSince the middle pleistocene there were three pleind potash salt deposits appeared at about 16-19 ka B P. tocene glaciations in the Tanggula Mountains, namelyand formed a dry salt lake due to an extremely dry cli- Kunlun Ice Age, Penultimate Ice Age, and Last Ice Agemate. The deposited loess both at the east bank of as well as two late holocene glaciations namely neo-Golmud Reservoir and Nachitai terrace(18.931-15377 glaciation and Little Ice Age ( Jiao and Shen, 2003; Duanka B P)are also the products of that period. All of the- et al., 2005). At the peak of the little Ice Age inse agree well with climatic change in the Tibetan Plat- Tanggula Mountains, the late holocene glacier waseau. Meanwhile, it possibly indicates, due to extreme 0.5-2.0 km longer, and 8%12% larger than at present,low temperatures, that permafrost formation might and the snowline was 20-65 m lower than todays snowconsume a large amount of fresh water because of gas line. The maximum, middle and minimum of extendinhydrate generation. The salinization of lake water is distances, increased areas and lowering snowlines cor-closely related to gas hydrate formation since they have responds to the eastern, middle and western segments oftemporal correlationthis glacier. The extending extent of the PleistoceneAccording to literature about the history of hydro- glacier during the Neoglaciation is 3.0-5.0 km awaycarbon generation(Zhao et al., 2000b), the major period from the end of the present glacier. During lgm, glacialgenerating hydrocarbons in main petroleum generating line at Tanggula Puerto descended to an altitude ofbasins, such as the Qiangtang Basin, is late Jurassic to 5,040-5,060 m. The glacier at that time was 3.0-10.0 mearly Cretaceous, while regional or local secondary hy- longer than present, with an area 1.54.5 times largerdrocarbon generation mainly occurred in the early Ter- than today, and descending snow line to 140-250 m Jiaotiary. Before the rapid uplift of the Tibetan Plateau, both and Shen, 2003 ). During the last glacial period in thestructural and thermodynamic forces combined to drive Middle Pleistocene, the glacier was transitional betweenhydrocarbon migration, leading to alternating destruction monsoon continental and oceanic, with a snow line ofand accumulation of petroleum reservoirs. Since about 5, 238 m in altitude, mainly formed down-incised troughs3.4 Ma B P, frequent seismic and fault activities follow- in valleys the Kunlun Ice age, which is the earliest anding rapid uplift of the Plateau provided available chan- largest ice age during the quaternary glacial period, isnels of migration for hydrocarbon gas. Glacial and peri- possibly a monsoon marine ice cap, which formed a highglacial processes are widespread during the quaternary, glacial drift platforms and deep secluded valleys(Dengwith pressure from ice cover promoting gas hydrate sta- and Zhang, 1992). The glacial extent at Tanggula Mounbility within underlying deposits. This forms a stabile tains during maximum ice age, according to statisticszone of gas hydrates under conditions of suitable tem- from the central and western segments, is 24, 500 km,perature and pressure, which are eventually preserved 12 times larger than present (Shi et al., 1995). The totalunder frozen cover through rapid decrease of Tibetan area of the Tanggula Quaternary glacier(Figure 3 )rangPlateau temperatureses between 36,000 and 40,000 km 16-18 times largerthan present (Jiao and Shen, 2003)4 Coupling relationships between glacial formationSurface indications of petroleum have been found atevolution and gas hydrate accumulation and pool periglacial positions of the ice cap during maximum glaformingcial period(Figure 3), such as at Anduo, Yanshiping, andAngdaercuo(Zhao et al, 2000b; Wang et al., 2001)The formation process of stabilized zone and res- These petroleum indicators occur mainly in fractures orir of gas hydrates in a terrestrial permafrost regionin crystal caves, consistent with Jurasoverlyingd hydrocarbon atOiang et al., 2002). An ice layer of 3-4 m thick will the Anduo 1 14 highway maintenance station indicatesad to a geological static loadof 2.. 600 that alkane is domiith carbons on theN/cm? in the underlym, forcing fluids, suchincluding"C22 and" C24 Naphthenic hydrocarbonwater,oil and gas, out of fine dispersed rocks with is also relatively high, while most of alkane and isoparweak permeability into strata with good reservoir prop- affin before C20 are lost. Compared with J3s limestone inerties. The strong forces produced by flowing water this region, the maturity of crude oil is relatively higher,during the process of glacier movement will washout and deviate from evolutionary curve of normal hydroand destroy reservoirs of oil and gas, causing hydro- carbon source rocks, which indicate oil seepage has beencarbon advancement in the direction of glacier move- subjected to secondary migration for some distance. Inment. Thus, it changes the distribution of hydrocarbon the process ofight hydrocarbons in the oilagain, Glacier movement force soil and gas from below seepage is almos中国煤化工1 to relativelyCNMHG696Qiang Zhou et al, 2013/Sciences in Cold and Arid Regions, 5(6): 0691-0697strong biodegradation(Zhao et al, 2000b). The late mi- movement which is helpful for the generation of gasgration of oil seepage might be affected by glacial hydrates92030EModem glacierPariglacial boundary of ice capBalance line33°30Nndong Peaked during maxing0102030km33°00上32°30NFigure 3 A comparison of present and lgm glacier extent in the Tibetan Plateau(Shi et al., 1998)5 Conclusionseau, again producing hydrocarbon migration. Pressure ofice cover forces out free hydrocarbon gas from withinBased on extensive literature, we preliminarily con- underlying sediments incorporated with water, forminclude that Mesozoic marine hydrocarbon source rocks, gas hydrates, which are then preserved and covered bywidely distributed in the Tibetan Plateau, provided sig- frozen layers produced by sharp falling temperatures innificant source material for formation of gas hydrates in the Tibetan Plateau.permafrost. Carbonate rocks and mud shale, the majorTherefore, we conclude that gas hydrate has goodsource of hydrocarbons, is an important reservoir stra- spatio-temporal coupling relationships among conditionstum for gas hydrates. According to research on the his- of accumulation and preservation based on compressivetory of hydrocarbon generation, the main period of hy- analysis of petroleum generation, evolution, uplift odrocarbon generation in the Qiangtang Basin of the Ti- Plateau, formation of frozen earth, glacial advancementbetan Plateau, is late Jurassic to early Cretaceous. Sec- and regondary generation of hydrocarbons, regionally or locally,mainly occurred in the Early Tertiary Before rapid uplift Acknowledgmentsof the Tibetan Plateau, petroleum reservoirs had been We would like to thank for anonymous reviewers helpalternatively destroyed and accumulated due to com- ing improving this manuscript. Thanks are also given tobined structural and thermodynamic forces driving hy- the authors whose literatures are incited here, especiallydrocarbon migration. Since about 3. 4 Ma B P, the Plat- those not listed below. This paper is supported by reeau has been subjected to widespread glaciation and search Project No. 200420140001 of China Geologicalperiglacial processes, following strong uplift of the Plat- Survey中国煤化工CNMHGQiang Zhou et al, 2013/Sciences in Cold and Arid Regions, 5(6): 0691-0697697REFERENCESTechnology Press, Guangzhou, China, pp, 415-446YF, Zheng bX, 1997. Glaciers and environments during the lasChen DF, Wang MC, Xia B, 2005. Formation condition and distribuGlacial Maximum(LGM)on the Tibetan Plateau. Journal of Glaction prediction of gas hydrate in Qinghai-Tibet Plateau permafrostiology and Geocryology, 19(2): 97-11348Shi YF, Zheng bX, Li SJ, 1995. Studies on altitude and climatic enviChen Kz. Bowler JM. KeltsK. 1990. Palaeoclimatic evolution withinronment in the middle and east parts of Tibetan Plateau duringthe Qinghai-Xizang(Tibet) Plateau in the last 40,000 years. QuaQuaternary Maximum Glaciation. 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