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Petroleum Geology & Potential
Sedimentary Basins
Junggar Basin
Tarim Basin
Qaidam Basin
Ordos Basin
Songliao Basin
Boa Bay Basin
Sichuan Basin
Jonathan Basin
Subbed Basin
Naming Basin
Baize Basin
East Sea Basin
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           There are 3 million km2 of offshore area where oil exploration began in 1960's. In the initial years, exploration was focused in shallow-water area such as Bohai Sea; after 1979, in cooperation with foreign oil companies, exploration was expanded to most offshore basins. Oil exploration has now been carried out in each of the offshore basins.
           In the past twenty years, a series of sedimentary basins rich in hydrocarbon potential have been discovered in Offshore China areas. They cover a total area of nearly 1 million km2. These sedimentary basins, from north to south, are Bohai Basin, North Yellow Sea Basin, South Yellow Sea Basin, East China Sea Basin, Okinawa Trough Basin, West Taiwan Basin, Southwest Taiwan Basin, East Taiwan Basin, Pearl River Mouth Basin, Beibu Bay Basin, Yinggehai-Qiongdongnan Basin and basins in the south part of South China Sea, etc.
           Oil and gas exploration in offshore China has mainly focused on Bohai Bay, Yellow Sea, East China Sea and the northern continental shelf of South China Sea, where the predicted hydrocarbon resource potential reaches 27.53 billion tons of oil and 10.6 BCM of natural gas, while discovery rate there is only 18.5% and 9.2% for oil and gas respectively.
  Sedimentary Basins
         Junggar Basin
           The Junggar Basin, which is situated in the hinterland of Asia and far from the sea, is one of the major oil- and gas-bearing basins in western China and covers an area of 140,000 km2. Commercial oil flows of varying amounts have been found in Late Paleozoic, Mesozoic and Cenozoic strata.
           Sedimentary formations, including Carboniferous, Permian and Meso-Cenozoic, appear only in the basin's marginal areas. A vast area inside the basin is covered by the Quaternary. The Upper Carboniferous and the Lower Permian are transitional sediments of marine to continental facies. The Upper Permian is a grayish-black, burnable organic rock formation. The bottom of the Mesozoic (P2-T1) is a 200-1200m thick molasse red-bed, its middle part (T2-J2) is coal-bearing sediments, 250-4000m thick, and the upper part (J3-K1) is a formation of red-beds and varicolored sandstone and mudstone, 210-2,500 m thick. The Cenozoic consists mainly of red-beds of clastic rocks.
           The most important source rock is Upper Paleozoic. The coal series of the Mesozoic is confined only to the central-southern part of the basin and has possible gas potential. Significant Cenozoic source beds only occur in the southwestern part of the basin.
           Reservoirs are mainly terrestrial lacustrine/fluvial facies sandstone and conglomerate.
           The traps in this basin are characterized by their variety in form and type. But rich hydrocarbon accumulations are controlled by the main thrust fault. Different kinds of traps and various types of reservoirs occur along both sides of the fault, such as the fault-barriered oil pools, fault block-anticlinal oil pools, buried mountain-unconformity stratigraphic-trap oil pools, basement oil pools, stratigraphic-trap oil pools, bitumen-sealed trap oil pools, anticlinal oil pools, etc.
         Tarim Basin
           The Tarim Basin located between the Tianshan and Kunlun ranges covers 560,000 km2 and is the largest in China. Its size and shape is comparable to the Sea of Japan, a modern back-arc basin. Commercial oil and gas flows of varying amounts have been found in Jurassic and Tertiary sandstone and Cambrian-Ordovician carbonates.
           The crystalline basement of the Tarim Platform is composed of Archeozoic and Proterozoic rocks. The marine sedimentary cover formed in the Late Proterozoic and Paleozoic. During the Mesozoic and Cenozoic, a continental basin structural regime formed. The source rocks are Cambrian-Ordovician, Carboniferous-Permian, Triassic-Jurassic, Upper Cretaceous-Lower Tertiary and Upper Tertiary.
           Various kinds of traps make different kinds of petroleum reservoirs possible, including anticlinal and faulted reservoirs, lithologic-structure reservoirs and the basement reservoirs related to unconformities.
           Qaidam Basin
           The Qaidam basin located in NW China and situated in the northeastern Qinghai-Tibetan Plateau, is a typical Meso-Cenozoic nonmarine petroliferous basin. The area of Meso-Cenozoic deposits is about 96,000 km2, with a maximum sediment thickness of 16 km.
           The basement of this basin is lower Paleozoic and pre-Paleozoic crystalline rock and granite. The Mesozoic (Jurassic and Cretaceous) sedimentary rocks are found only in the northern part of the basin. The overlying sedimentary strata start from Paleogene.
           The Lulehe formation of Paleocene age, to the lower part of lower Ganchaigou formation of Oligocene age, consists of brownish-red mudstone interbedded with conglomerate and sandstone. The 400-1900 m. thick formation underlay the entire basin. The upper part of lower Ganchaigou formation to upper Ganchaigou formation of Miocene age consisting of dark gray mudstone intercalated with marl and siltstone, are wildly distributed in the western part of the basin. The Pliocene consists mainly of brownish red and grayish green mudstone interbedded with conglomerate, granulite and sandstone. In Quaternary, the landscape of Qaidam basin became wide fluvial plain with several remnant salt lakes in it.
           In the northern part of the basin, the Lower-Middle Jurassic is the source rock and the Tertiary sandstone is the reservoir. In the western part of the basin, the thick Oligocene and Miocene mudstone is the major source rock and the Tertiary sandstones below and above the source rock are reservoirs.
           There are different types of oil and gas pools in the basin: lower reservoir-upper source-rock type, lower source-rock-upper reservoir type, oil and gas pools of laterally connected source- and reservoir-rock assemblages, carbonate fissure-vug-type oil and gas pools.
           Ordos basin
           The Ordos basin, with an area of 250,000 km2 is the oldest craton in China. The basement structure of the Ordos basin is double-layered. One layer is of Archeozoic granulite lithofacies. The other layer is dominated by Lower and Middle Proterozoic greenschist facies.
           The development of the sedimentary cover can be divided into five evolutionary stages as follows: aulacogen basin in the Middle-Late Proterozoic continental rift stage; Early Paleozoic marine carbonate platform stage with a geosyncline-platform tectonic regime; the Late Paleozoic (C2) to Early Mesozoic (T2) intermediate stage characterized by the change from marine facies to inland basinal facies; the formation and development of the Mesozoic polycyclic inland basin; the uplift and disintegration of the basin and the developing stage of the Cenozoic graben system.
           There are multiple sequences of source rock in the basin, such as Early Paleozoic carbonate rocks, Late Paleozoic coal measures and Mesozoic shales of the Yanchang and Yanan formations. The total thickness of the source rocks exceeds 2000 m.
           There are different types of oil and gas pools in the basin: lithologic pinchout oil and gas pools, sand lens oil and gas pools, stratigraphic oil and gas pools, weathered crust oil and gas pools, anticlinal oil and gas pools.
           Songliao Basin
           The Songliao Basin of northeast China is a large Meso-Cenozoic continental sedimentary basin, with the total area of 260,000 km2. The basement of the basin consists mainly of Paleozoic and pre-Paleozoic metamorphic rocks and various igneous rocks.
           The Jurassic deposits are sandstone, shale and conglomerate with coal intercalations. The climax in the development of the basin was in Cretaceous time. The process includes three stages, i.e., a rift-valley stage of taphrogeny, a subsiding stage of a large sedimentary depression, and shrinkage and uplift stage. Fluvial-lacustrine sediments attain a total thickness of more than 5000 m, and comprise the main source rocks and reservoir rocks.
           The three main oil source rocks of the Cretaceous system in the basin are Qingshankou 1, 2-3, Nenjiang 1, which are all abundant in organic matter. There are different types of oil and gas pools in the basin: anticlinal oil and gas pools, lithologic oil and gas pools, lithologic-structural oil and gas pools, subtle oil and gas pools.
           Bohai Bay Basin
         The Bohai Bay Basin covers 200,000 km2 Bohai Bay and its coastal areas.
           The Bohai Bay basin was formed and evolved on the basis of the ancient North China Platform through the platform-development period of the Middle-Upper Proterozoic and Paleozoic, and the faulted-subsidence development period of Mesozoic and Cenozoic.
The basement is composed of metamorphic rocks with ages of 1.7-3.7Ga.
           The depositional history of Paleogene Bohai Bay basin consists of 4 cycles, namely the cycle of kongdian formation, cycle of 4th and 3rd members of Shahejie formation, cycle of 2nd and 1st members of Shahejie formation and cycle of Dongying formation. The Kongdian formation represents deposits in the initial stage of rifting. The Shahejie formation makes up the frame of the basin deposits with expansion and contraction, deep faulting and uplifting. The Dongying formation is the record of the late stage of rift-faulting when contraction dominates with intercalations of smaller scale. The middle part of Kongdian formation's dark mudstone is the first source bed of the basin. The 3rd and 1st members of Shahejie formation are the two major oil-generating beds.
           The reservoir rock bodies can be classified into five types, i.e., alluvial-fan, delta, lake-floor-fan, clastic-limestone or algal-reef, and lenticular sandbodies.
           There are different types of oil and gas pools in the basin: the faulted basement-block pools, folding structural pools, stratigraphic-lithologic pools, draped structural pools, reverse-drag structural and stratigraphic pools and heavy-oil pools.
         Sichuan basin
           There is a long history of exploration and exploitation in the Sichuan Basin. A complete system of drilling, recovery, transportation and utilization had already been developed in ancient times. The Sichuan basin is a large-sized oil- and gas- bearing basin in the Yangze paleoplate. Its basement is metamorphic rocks of Pre-Sinian.
           In the Early Paleozoic, the regional elevation and subsidence resulted in large-sized uplift and depression structures, and it was dominated by neritic platform deposits. In Devonian and Carboniferous, the Upper Yangtze Craton was gradually rising from west to east to form the Leshan-Longnusi paleouplift, which later underwent denudation. The process from the vast transgression in the Early Permian to the salting and shrinking of the sea basin in the Middle Triassic formed a complete and sequential sedimentary cycle. Since the Late Triassic, the margin of the basin uplifted and fluvial-lacustrine sedimentary system distributed in the whole basin. At the end of Early Cretaceous, the basin experienced folding and uplift.
           The sediments of the Early Paleozoic are mainly polycyclic, neritic-platform facies in which there are many oil- and gas-generating strata. The Triassic sediments developed bay facies and transitional marine and continental facies which intercalates with the lacustrine-bog facies. The two types of deposit are superimposed upon each other and can provide considerably abundant gas resources.
           There are different types of oil and gas pools in the basin: the anticlinal pools and stratigraphic-lithologic pools.
            Jianghan Basin
           The Jianghan Basin is located in the middle part of Jianghan plain, Hubei Province, with an area of 28,000 km2. Structurally, the basin is located the middle part of Yangtze depression in Yangtze paraplatform. It is a Mesozoic-Cenozoic extensional-fault basin that developed after the Yanshan movement.
           Because of regional structural movement, basement differential subsidence and block-faulting, a series of sags and depressions were formed in the Jianghan basin. The basin is divided into eleven sags and four uplifts
           The Cretaceous-Eogene sedimentary sequence is divided into Yuyang, Shashi Xingouzi Jingsha, Qianjiang Jinghezhen and Guanhua formations in the Jianghan basin.
           There are four source rocks in the basin. They are Yuyang formation, upper member of Shashi formation, lower Xingouzui formation and Qianjiang Formation. Of them, Q3 and Q4 members of Qiangjiang formation and lower member of Xingouzui formation are important source rocks. According to our research result, there are six petroleum systems (Jingling, Mianyang, Chengtuokou, North Qianjiang, South Qianjiang and Xiaoban) and seventeen plays.
           Subei Basin
           The Subei basin covering 35,000 km2 is located in northeast Yangtze continental mass and belongs to the offshore part of Subei-South Yellow sea basin. It is a Mesozoic-Cenozoic continental basin that developed after Yizhen movement of Yanshan structural cycle. According to the distribution and development of Eogene strata, the Subei basin is divided into two depressions (Dongtai and Yanfu depression) and one uplift (Jianhu uplift).
           The Mesozoic-Cenozoic sedimentary sequence with the thickness of over 7,000 m is divided into Cretaceous Taizhou formation, Eogene Funing Dainan and Sanduo formations, Neogene Yancheng formation and Quaternary Dongtai formation in Subei basin.
           In Subei basin, there are six source rocks from Cretaceous to Eogene. They are Tai-2 member of Taizhou formation, Fu-1, Fu-2, Fu-3 and Fu-4 members of Funing formation and Dai-1 member of Dainan formation. The source rocks are widely distributed over these depressions with the total thickness of over 400 m.
           There are three petroleum systems and eleven oil-bearing strata. The petroleum systems are Taizhou-Funing system, Dainan-Sanduo system and Mesozoic-Paleozoic system.
           Nanxiang Basin
           Nanxiang basin with an area of 17,000 km2 is located in the Qinling-Dabie geosynclinal region, south of Henan Province, and is a Mesozoic-Cenozoic intermountain rift basin formed at the end period of the Yanshan Movement. Since the late Cretaceous, the Nanxiang basin undergone two development stages (faulting and depression), and the former stage is the main period of the sags and uplifts formation.
           The Nanxiang basin includes three sags (Miyang, Nanyang and Xiangyang) and three uplifts (Shigan, Sheqi and Xinye). The sags of the basin are controlled by faults, which include the pre-Mesozoic NW faults active chronically and the new NE faults formed during the Yanshan movement period, and they cut the basin into square figures by which the sags and the uplifts are distributed alternately. The difference of sedimentary thickness, distributing area, hydrocarbon-generation condition and accumulation degree is very distinctive in the three sags, of the three sags, the hydrocarbon accumulation condition of the Miyang sag is the best and the Nanyang is the second, and no show has been discovered in the Xiangyang sags.
           The upper Cretaceous and Tertiary strata of the basin developed on the bases of the Proterozoic metamorphic rocks. The Paleogene period is the main stage of the basin formation and the lower Tertiary is the thickest (over 6000 m). From younger to older, it could be divided into Yuhuangding-Dacangfang formation, Hetaoyuan formation and Liaozhuang formation. The Hetaoyuan formation belonged to the stable sedimentation of the late-Eocene lake, and it consists mainly of dark-gray shale and sandstone deposit of deep lake environment. This is as main exploration target formation.
           Baise Basin
           Baise basin is located in the west-south of Guangxi Chuang municipality. It is the popedom of Baise, Tianyang and Tiandong counties. It lies between east longitude 10634'-10721' and north latitude 2323'-2347'. Its area is 830 km2.
Basin basin is a residual basin in Eogene system superimposed on Triassic basement. From the lower to the upper: strata are the Hongseyan formation in lower and middle Eocene in Eogene system, Nadu formation in upper Eocene, Baigang formation in Oligocene, Fuping formation in Miocene of Neogene system, Jianduling formation in Miocene and Pliocene, Changsheling formation in Pleistocene in Quaternary system and Holocene series.

Baise basin is a Mesozoic inland rifted-basin developed on fold basement in middle Triassic, controlled by north-west tectonic. From west to east, Baise basin is divided into 5 secondary structural units: Baise depression, Sitang swell, Tianyang depression, Nabai swell and Tiandong depression. There is north-east fault between units. Depressions in basin are all asymmetric syncline which is flat in the south and steep in the north. Its subsidence center is in the north of the basin.

Oil source bed, reservoir and caprock:
The oil source bed in Baise basin is mainly Nadu and Baigang formations. Its main reservoir is middle Triassic Nadu formation and Baigang formation in Eogene system. Reservoir types are porous-type sandstone and fracture-type carbonate.

Oilfields and oil reservoir type:
Since Linpeng oil-bearing structure was known in 1959, Shangfa, Zimou, Lunwei, Tangzhai, Huacha, Nakun and Leigong, etc., oilfields have been found. The oil and gas pool type is mainly structural, fracture, stratigraphic unconformity and lithological reservoirs.

           East Sea Basin
           East sea basin is located in the east to Fujian and Zhejiang provinces and in the north to Taiwan Island. Its area is 260,000 km2. It is a large-scale sedimentary basin with its main clastic sediment of Caenozoic era. Mesozoic and Caenozoic strata were developed well in East Sea basin.
           Structures: East sea basin is a Cenozoic back-arc spreading basin. It has two-layer structure with half graben-type depression in the upper. From south to north, this basin is divided into Taixi, Taibei, Zhedong and Fujiang depressions. Every depression is divided into secondary sags and swells.
         Oil and gas exploration work in East Sea basin is mainly concentrated on Xihu sag and Taibei depression. The oil source bed in Xihu sag is Pinghu formation of Eocene age, and its reservoir is sandstone of Eocene and Oligocene age. The oil and gas pool is anticline-type and stratigraphic-structural-type. Up to now, Pinghu and Chunxiao oil and gas fields have been found in East Sea basin.
  Resources Potential
           Although there are complex geological settings, imbalanced resource structure and main oilfields' decrement in China, it has great potentials of oil-gas resources.
  1. Totally, the extent of exploration has been relatively low and uneven in most of the sedimentary basins all over the China. Especially the oil-gas exploration and development in the offshore regions has been at the initial stage. Some big oil and gas fields have been discovered. For example, in 1999-2000, huge oil-gas fields, such as No. 2 Kela and Sulige with the proven reserves of over 7 Tcf and Penglai 19-3, an equipped huge oilfield with the proven reserves of 4.4 billion barrels, have successively been discovered.
  2. Lots of new areas still are under explored such as basins in the south and other areas. It has been predicted that these areas hold in store rich oil-gas resources of 270 billion barrels; over 30% of total oil-gas resources.
  3. There exist many fields and strata that have good resources potentials and perspectives, for example, pre-tertiary in the eastern regions of China, deep-water regions in the offshore and thrust blocks in the both southern and northern sides of Qinglin-Dabie Mountains.

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Last Update: 8 August 2002