CNPC＇s Future Exploration Targets for Giant Gas Fields

CNPCS Future ExplorationTargets for Giant Gas FieldsFan Wenke, Zhang Fudong2, Wang Zongli?, Yang Dong, Yang Shen?(1. Petro China Exploration and Production Company; 2. Langfang Brach of PetroChina PetroleumExploration and Development Research Institute)(from Issue No. 2)Potential exploration targets for giant gas fields the deep clastic sediment in Bohai Bay Basin.DespiteBased on the distribution of remaining gas resources, the discoveries, the exploration rate for theseareashe exploration targets selection as well as an analysis of only 24.8% and a larger chunk is remained to be foundcontrolling factors for giant gas reservoirs( proven gas The upper Paleozoic in central and eastern Erdos and thereserve in place 30 bcm), CNPC determined to focus Xujiahe Formation in Sichuan are thought to be the recentits exploration in the Sulige area and east part of Erdos major exploration targets for the CompanyBasin, the Xujiahe Formation and reef flat in central (1) Exploration targets for giant gas fieldsSichuan Basin, Tazhong and Kuche areas in Tarim Basin, around the Sulige gas field and eastern part of the Erdosthe deep Chuanglin and Xujiaweizi areas, and Yingtai Basinfaults in Songliao Basin as well as Ludong-Wucaiwang The upper Paleozoic in Erdos Basin contains gas ofarea in Juggar Basin. Specific potential targets include 640 bcm. With an exploration rate of merely 25%, provenlithologic gas reservoirs in vast area of sandstone, marine gas reserve is about 160 bcm and about 480 bcm ofcarbonates, thrust belts of foreland basins, volcanic gas remaining gas reserve is waiting to be explored. The upperreservoirs, biogas reserves as well as unconventional gas Paleozoic in the basin developed two sets of sedimentaryreservessystems: the north system and the south system. The northsystem harbors four major drainage systems, namely theLithologic gas reservoirs in vast area of sandstone Shengmu, the Yulin, the Sulige and the Western PartBy the end of the Eleventh-Five-Year-Plan period, Meandering stream is found to be developed in the eastNPC's effort in lithologic gas reservoirs search had and braided channel deposition is in the west. Three setspaid back. With the discovery of the Sulige gas field, of gas-bearing formations(the He-8, Shan-1 and Shanthe company found multi-trillion cubic meters of gas in 2)are formed in these wide and out-stretched channelsvast area of sandstones. The Xujiahe Formation was also and are regarded as the realistic exploration domainsregarded as a realistic hope for a gas producing region since three gas fields(the Sulige. Yulin, Shengmu)werewith trillion of gas reserves. Meanwhile, discoveries had discovered in si中国煤化工 with a resbeen made in the deep glutenite in Songliao Basin, the potential of 3(od ihCN MH GIgh large scalethrust belts of foreland basins in northern Tuha Basin and exploration in eastern and western Sulige area. In the14 CHINA OIL GAS12OIL and GAS RESOURCESmeantime, areas adjacent to western andsouthern Sulige were also found to havegreat potential for gas reserves and wereered as the main exploration targetsin the future. The less important explorationtargets include the Shengmu-Mizhi and theGaoqiao in eastern BasinThe southern sedimentary system consistsof south-west and east-south drainagesystems, which control the distribution ofmajor gas-bearing reservoirs. The southwest system contains the Shan-I and He-8reservoirs and the east-south system isalient with its Shan-2-He-8 gas reservoirsThe potential of the two system is hugeas the exploration achieved gas shows inmany wells and one of them producedindustrial gas stream. The southwesternand west margin of the basin as well as thewest section of the Tianhuan depression are Jalso considered future exploration targetsand exploration of these areas are currentlyZhou /iping, General Manager"the Rapidly Growing World arChinese Gas Markets" indicating that striving for gas development is the(2)Potential exploration targets in centralstrategic choice for Chinese energy developnentSichuan Basin-the Xujiahe Formationlithologic-structural gas accumulations. The most recentThe potential exploration area in the central Sichuanpotential exploration targets include the Tongnan beltBasin is about 50,000 km and about 156 bcm of gas is and Anyue-Hebaochang belt in Hechuan-Anyun Blockying underneath. With an exploration rate of 35%, the Yingshan belt in Guangan- Yingshang Block, Xichong-area has a proven gas reserve in place of 55 bcm, leavingRenshou Block and Shehong-Nanchong Block. There are100 bem behind. During the Eleventh-Five-Year-Plan possibilities that a gas reserve of trillion cubic meters beperiod, the company had strengthened its exploration established after a faster exploration in all these blocksfor the area with a thorough high-resolution 2D seismicsurvey,thus providing necessary data for a faster further Marine carbonatesexplorationThe marine carbonates in areas where CNPC ownsThe Xujiahe Formation in central Basin is where mineral rights contribute a gas resource of 810 bem. Withmany sedimentary matter sources converge and the inter- an exploration rate of 20%, they offer a proven gas reservesuperimposition of several delta systems in the area forced in place of 163 bcm, leaving 647 bcm of gas behind to bethe sandbody to overlay one another. Large reservoirs explored. These carbonates are mainly distributed in threewere therefore developed in the diagenetic facies belt of cratons: Sichuan. Tarim and Erdoschlorite cement facies and dissolution facies. Since mostCNPC has been focusing its exploration on threeof the belt is located in the foreland slope belt of the late kinds of marine carbonates: the plat form margin reefsTriassic and near the hydrocarbon-generation center of the in the Permian-Triassic of northern Sichuan Basin, thewestern Sichuan Basin and the whole area is also located Cambrian-Ordovicientral and northern Tarimin a favorable place for hydrocarbon migration with Basin and the Or中国煤化工tern Erdoswest-ward large slope background, the central Sichuan Basin: the weatherCNMHG-CambrianBasin is favorable for the formation of large lithologic or and the Permian-Triassic from central Sichuan Basin, theCHINA OIL& GAS15No.3,201Ordovician from the central and northern Tarim Basin, and reservoirs in the western part, adding proven gas reservethe Ordovician in central Erdos, and the grain banks and in place of 20 bcm. With further exploration, the marginsthe dolomite in the Permian-Triassic of central Sichuan may bring 30-50 bcm of gas for the companyBasin, the Cambrian-Ordovician of central, western, and Another realistic exploration target in central Tarimeastern Tarim Basin and the Ordovician in central and Basin is the large karst slope in the Yingshang Formationwestern Erdos Basinfrom the mid and lower Ordovician. Progress was madeReef banks in the Changxin-Feixianguan Formation of in the well Tazhong-83 in 2006 and from 2007 to 2008Sichuan Basin, platform margin and karst slope in central another three wells yielded high rate of industrial gasTarim Basin and the lower Paleozoic in the western flow. In 2008, CNPC finished the survey of the TazhongJinbian gas field in Erdos Basin, are considered key areas 83 well block, And also in the same year, the companyfor recent exploration of the company.achieved high rate gas flow in two wells, the Zhonggu-8(1) Exploration targets in Sichuan Basin-the and the Zhonggu-21. In 2009, CNPC confirmed theChangxing-Feixianguan FormationZhonggu-8 gas reservoir and in 2010 the Zhonggu-43The gas resource from reef bank in the Changxing. gas reservoir. The karst slope in the north part of centralFeixianguan Formation of Sichuan Basin is about 220 Tarim Basin is very promising area as it added proven gasbem. With an exploration rate of 10%, the proven gas nerves in place of 0.3x10"m, and contributed a three-reserve from the facies is 22 bcm. Platform margins in level oil and gas equivalent of 462 million tons. Thethe Kaijiang- Liangping and the Exi-Chengkou troughs potential exploration area in karst slope of the Yingshangin the area are regarded as potential exploration targets. Formation is about 2800 km with a potential oil and gasThe former contains reef bank of about 600km long and equivalent of 1500 million tons. Further activities may2 to 6 km wide. With an oolitic beach area of 8000 km, push the reserve figures higherthe place means bright exploration future. The Longgang (3) Exploration targets in Jinxi area of Erdos Basin-thearea in western trough is considered the biggest hope lower Paleozoic.for finding giant gas reservoirs especially after the The lower Paleozoic of the Erdos Basin has gasbreakthrough with the well Longgang-I in 2006. CNPC resources of 240 bcm. With an exploration rate of 18%had carried out thorough 3D seismic survey for the place the company confirmed a proven gas reserve in place ofand yielded very positive results. The latter is another 43 bcm, leaving promising resources behind. The lowerexploration targets for potential giant gas field. Currently, Paleozoic of the basin was once famous for the discoverythe wildcat Zhuyuan-I in western trough was tested of the Jinbian gas field by the end of 1980s. However,with industrial gas stream, while well Feng-I in eastern until the year of 2009, the company had not made anyMacaoba area of the trough show traces of gasprogress in the formation. In 2009, the company realized(2)Exploration targets in Central Tarim Basin-the that the weathered crust in the west and southeast partsPlatform margin and karst slopeof the field have similar reservoiring conditions as thatSeveral platform margins were developed during the of the Jinbin. Then it changed its exploration strategydeposition of the Cambrian-Ordovician in Tarim Basin. and tested the well Suwu-l in the west part and the wellAccording to estimation, these margins contains gas Yi-6 in southeast part with industrial gas flows. Later,resource of over 100 bcm. Three platform margins located the company moved further toward west and find gasin the central basin are considered most promising with reservoirs with well Su-203 and well Su-332 in the lowerbreakthrough being made in one of them -Tazhong-1 Paleozoicmargin in central basin. The slope break-reef bank The potential exploration area in Jinxi is about 4500complex in the Tazhong-I margin is 220 km long from km. Research indicates that the Ordovician of the belteast to west and 5 to 18 km wide from south to north. developed multi-stage deposition of algae bank facies,Potential exploration area in it is about 1500 km. The which vertically imposes one another and horizontallymain part of the margin probed with 3D seismic survey, circles around中国煤化工 e east. By theconfirm three oil and gas fields(Tazhong- 26, Tazhong- 62 end of Caledgion under theCNMHGand Tazhong-82 )in the eastern part, and two oil and gas unconformity earyoung, forming16 CHINA OIL GAS万序数据012OIL and GAS RESOURCESetched grooves. These grooves transformed the algae bank margin of Qaidam and western margin of Erdos are alsofacies and formed dolomite reservoirs of multi-layer algae thought to be worth of exploringbank facies. Currently, CNPC has found 4 wells with high (1) Foreland thrust belts in Kucherate of gas flow in the area, indicating four promising CNPC's exploration area in Kuche foreland thrustexploration targets. The company decides to follow its belt in Tarim Basin is 28000km, contains a gas resourcegeological understanding of"groove controlling the of 320 bcm. However, more work needs to be donereservoirs"and is looking forward for a better resultsince the prove gas reserve in place is only 54 bem withApart from the above-mentioned areas, the tough an exploration rate of 17%. Conditions of the area arein Qinqi, dolomite in Masi and pre-salt in the east, are considered favorable for gas reservoiring. The 2D seismicconsidered the major potential exploration targets for the survey carried out by the company has covered the fourlower Paleozoic in Erdos Basin. These areas are barely belts(from deep to shallow in Kelasu structure zoneexplored and need a thorough explorationand confirmed the existence of right structures and trapsfor gas. A batch of traps is also confirmed in Dabei andForeland thrust beltsKelasu structural belt. Further exploration in the belt mayCNPC has been focusing its foreland exploration in bring trillion cubic meters of gas reserve to the company.five major basins: Tarim, Sichuan, Juggar, Erdos and (2) Foreland thrust belt in southwestern Tarim BasinQaidam Gas resource from CNPC's foreland thrust belts CNPC's exploration area in foreland thrust belt inis about 730 bcm. The exploration rate is rather low only southwestern Tarim Basin is also 28000 km,contains1% and the proven gas reserve in place is only 80 bcm. gas resources of 110 bcm. However, further explorationThe Kuche and the southwestern part of the Tarim basin needs to be carried out since the prove gas reserve inare considered by the company as the most promising place of the area is only 4 bcm with an exploration ratetargets, while southern Juggar and northwestern Sichuan of 3.6%. The foreland belt in the area is buried by thickare regarded as having great potential. Then the northern loess and the quality of seismic data is rather poor中国煤化CNMHCHINA OIL& GAS17No.3.2012oIL and GAS RESOURCESSince the discovery of Kekeya gas field in 1977, the the central uplifting and eastern part. Breakthrough wasarea has yielded no significant discovery whatsoever. made with well Longsheng-101 and Longsheng-2 DuringHowever, the advancement of the wide line 2D seismic the drilling, CNPC found two favorable belts for gassurvey technology has greatly enhanced the quality of reservoirs with CO, content of 1%: the southern upliftthe data and confirmed 22 traps in 3 rows of structures. and the reverse structural belt in Wukeshu area(with anThe biggest discovery in more than 30 years is the well volcanic rock area of 400km). Current exploration resultsKedong-l drilled in 2009 and producing high rate of gas show that the Yingshan fault contains a gas resource of 23flow in 2010. Exploration shows 12 traps in 3 rows of bcm. With industrial flow from well Yingshen-2, CNPCstructures in the Kedong zone. These traps have an area of decided the fault to be a target for finding giant volcanic794km, contain a gas resource of 61.5 bcm, condensate gas reservoirs.1.46 million tons. The breakthrough in the well Kedong-1 In addition, three faults, namely Dehui, Gulong andopened a hopeful door for the exploration of the whole Lindian, are also CNPC's future exploration targets forareavolcannIc gas reservoirs(2) Volcanic gas reservoirs in the Carboniferous ofVolcanic gas reservoirsJuggar BasinVolcanic gas reservoirs owned by CNPC are mainly Present exploration and research show that thedistributed in five basins, i. e. Songliao Basin, Juggar Carboniferous volcanic rocks are broadly distributed inBasin, Bohai Bay Basin, Sichuan Basin and Tarim Basin. northern Xinjiang Autonomous Region. Large areas ofThese reservoirs contain a gas resource of 310 bcm, marine hydrocarbon source rocks were well developedamong which only 40 bcm of gas has been confirmed in the place. CNPC started to explore and study theand the exploration rate is only 13%. Giant gas fields Carboniferous formation in 2007. And in 2008.thewith proven reserve of more than a 100 bcm were company found the Kelameili gas field with a proven gasdiscovered in the Xujiaweizi fault and the Changlin reserve in place of 10.58 bcm in Ludong-Wucaiwan areafault in deep Songliao basin and the Ludong-Wucai area of Juggar Basin. Since then, the area has been consideredof the Juggar basin during the past few years. In 2008, having great potential for giant gas fieldnew breakthrough was made in the Yingtai fault of deep Apart from that, positive results have been achievedSongliao Basin and the Wucaiwan depression of the in the Wucaiwan depression-Baijiahai uplifting, theuggar Basin, making the two basins the key exploration Dishuiquan depression and the Shixi uplifting, thustargets for volcanic gas reservoirs. The faults of Changlin, they are regarded as the next exploration targets by theXujiaweizi and Yingtai in Songliao Basin, Ludong- companyWucaiwan in Juggar Basin are the four realistic targets forfinding reserves in the near future, the faults of Yingshan- BiogasShuangcheng, Gulong, Lindian, Dehui in deep Songliao CNPC,'s biogas resource (about 390 bcm) is mainlyBasin and the north and central part in deep Juggar Basin distributed in the Quaternary of Qaidam Basin, theare considered areas that require further exploration and Cretaceous of Songliao Basin and the Tertiary of Bohathe Permian in Sichuan Basin, the Triassic in Bohai Bay Bay Basin. In 1964, the Shebei-1, China's first biogasBasin and other faults in Songliao Basin are also regarded field, was discovered in the Sanhu area of Quadam Basinhaving some potential for this kind of gas reservoirsBy now, CNPC has found 3 giant biogas field and more(1) Volcanic gas reservoirs in deep Songliao Basinthan 30 gas reservoirs, with an accumulative provenThe exploration area in the Xujiaweizi fault of the reserve of 30 bcm(exploration rate of 7.7%)basin is about 5350 km. Remaining gas resource is about The biogas potential in the Sanhu area in Quadam64 bcm, mostly distributed in three exploration blocks: Basin is regarded highly by the company. The SanhtAnda, Xudong and Zhanozhou. They are thought to has an area of 37000 km with 5 biogas fields in it.Itpossess the conditions for finding another gas reserve of contains biogas中国煤化工吗 of 105 bcm10 bcm. The Changlin fault has an exploration area of and proven bioCNMHGW-amplitude7044km' with well-developed volcanic structures. Gas structural gas reser\UrIcu Iu Sata shallower thanreservoirs with low CO, content are hopefully found in月方数2OIL and GAS RESOURCES1 800m in the Quaternary have been the key exploration The high points of anticline traps are where the gastargets for the area. In 2008, lithologic gas reservoirs were concentrates most. In 2010, the area had been exploredfound in well Tainan-9 and new gas-bearing formations with new seismic survey technology and the results werewere discovered through the well Tai6-31, shattering the positive, showing a huge exploration potentialmisunderstanding that biogas was only found in stratashallower than 1800m. It is safe to say that the area will Unconventional gasgain more biogas reserve after a thorough evaluation Unconventional gas refers to tight gas, coal-bedof maturing fields and a continuous exploration of methane, shale gas, hydrate and water-soluble gaslithological gas reservoirs and deep strataAs the world energy demand increasing with timeBiogas in shallow strata of northern Songliao Basin unconventional gas and its exploitation is gaining moreis another key exploration target for CNPC. The area and more attention all over the world. In the United Statescontains gas resources of 100 bcm in the Cretaceous with unconventional gas production is playing an importanta burial depth of less than 800m. Eleven biogas fields role in the country. In 2009, the country produced gas ofwere discovered in Aonan and Honggang and proven gas 59 bcm, among which the unconventional gas is 33 bcmreserve in place is about 2 bcm. Remaining gas potential is accounting for 56% of the country's total and surpassingstill huge. Study shows that the first and second members the conventional gas rateof the formations in the area are immature or low-maturityChina's unconventional gas resource is about 258 tcmgas source rocks and they are widely distributed and (trillion cubic meters), 4.6 times bigger than that of thecontrol the distribution of biogas. The anticline, sandbody, conventional. The accumulated prove gas reserve is aboutand the relationship between the sources, reservoirs 40 bcm, leaving behind a huge amount of unconventionaland faults, control the range of gas-bearing formations. gas to be explored Current exploration and research中国煤化工CNMHGe up to September 2, Puguang gas field has surpassed 20 billion cubic meters of gas output since being put into operation. The photo showsthe workers of initial gas station are checking the gas export facilitiesCHINA OIL GANo.3.2012OIL and GAS RESOURCESshow that coal-bed methane and shale gas are the future structures in the above-mentioned basins. CNPC's gasdomains for giant gas fields for the companyexploration is facing many challenges such as variousChina is abundant in coal-bed methane with a resource geological structures, numerous potential or seeminglyf 3580 bcm buried in strata shallower than 2000m. In potential targets and etc, however, the gas potential is stillterms of resources, it is almost as rich as conventional huge Beside conventional gas reservoirs, unconventionalnatural gas. The coal-bed methane is widely distributed gas such as biogas, coal-bed methane and shale gas, arebut relatively concentrates in north and northwest China also considered potential targets by the companywith low coal rank gas dominance By the end of 2010,CNPC had added proven CBM reserve in place of 19 Referencesbcm in the Qingshui basin and eastern Erdos Basin to [1] Zhang Wengzi, Wang Zecheng, Wang Hongjunits reserve base. In 2010, CNPC produced CBM of 2.8 et al. Geological features of recent large- and middle-million cubic meters, accounting for 54% of the country's sized gas discoveries in China and gas explorationtotal. There are 15 basins having more than 10 bcm of prospective in the 21st century. Gas and Earth Sciences,recoverable CBM resources. Among them, the Erlian 2005, 16(16): 687-692basin, east margin of Erdos Basin, the Qingshui basin and [2] Cheng Yongwu. Chinas gas industry developmentJuggar Basin are considered most promising for future in the 21st century. Gas Industry, 2000, 20(1): 1-4giant gas fields3] Dai Jinxing, Zou Caineng et al. ReservoiringChina has already initiated shale gas exploration conditions and controlling factors for Chiina's giant gasand development and gained some positive results. fields. Gas and Earth Sciences, 2007, 18(4): 473-484According to statistics, China has a shale gas resource [4] Wang Tingbing Controlling factors and explorationof 3070 bcm, mainly distributed in the marine shale of domains of large- and middle-sized gas fields in Chinathe Paleozoic in south and northwest China. In 2010. Oil and gas geology, 2005, 26(5): 572-589CNPC drilled the first shale gas well Wei-201 in southern [5] Dai Jinxing. Potential giant gas plays in ChinaSichuan Province. The well tested industrial gas flow after Explorers, 1996, 1(1): 6-9large-scale fracturing in the Cambrian and the Silurian. [6] Jia Chenzao, Zhao Wenzhi, Zou Caineng et alResearch shows that the key indexes of the black shale Geological theory and exploration technologies forin the Longmaxi and Qiongzhusi Formation of the lower lithology reservoirs for oil and gas. Petroleum explorationPaleozoic in Sichuan Basin are similar to that of the shale and development, 2007, 34(3): 257-272gas fields in the United States. They have a thickness of [7] Zhao Zongju, Fan Guozhang, Wu Xingning er40-50 m and are the most promising exploration targets. al.. Types, exploration domains and strategies of marineA preliminary study selected three potential blocks with a carbonate reservoirs in China. Marine oil and gas geology,total area of 13000 km. These blocks, namely Weiyuan, 2007,12(1): 1-11Changning and Wushun-Yongchuan, have favorable burial [8] Jia Chengzao, Song Yan, Wei Guoqi et aldepth and are considered hope for finding giant gas fields. Geological features and oil and gas accumulations inforeland basins of central and western China. GeologyConclusionfrontiers,2005,12(3):3-13CNPC's gas exploration is overall underway and [9] Zou Caineng, Zhao Wenzhi, Jia Chengzao et alits gas reserve will maintain a high growth speed in a The formation and distribution of volcanic oil and gasforeseeable future. During the Eleventh-Five-Year Plan reservoirs in sedimentary basin of China. Petroleumperiod, the company had achieved many progresses and exploration and development, 2008, 35(3): 257-271ositive results in its gas exploration, several large gas [10] Zhang Ying, Dai Jinxing, Lijian et al.Theproducing areas are at the sight and many potential areas geochemistry and exploration of biogas in China. Gasand targets present positive results. All these lay down industry, 2009.9, 29(9): 20-23a sound foundation for a rapid development of oil and]LioV凵中国煤化工 Renhe et algas for CNPC. In the future, the company will focus on The current situaCNMHGventional oilfinding gas reservoirs in large areas of sandstones, marine and gas development. Gas industry, ZUUy.9, 29(9):113-carbonates. thrust belts in foreland basins and volcanic 1162952