Table of Content

25 April 2005, Volume 26 Issue 2

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Record and narration of Academician Guan Shicong's style of geologic work

Sun Zhaocai

2005, 26(2):  132-140,167.  doi:10.11743/ogg20050201

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Academician Guan Shicong, a famous expert in regional geology and petroleum geology, has made outstanding contributions to Chinese geologic cause through geologic researches over 60 years. His main achievements in regional geology are verification, for the first time, of the existence of Longshan movement in southern Gansu,western Qinling area and establishment of the Ordovician stratigraphic system in Zhuozishan area. His main contributions to petroleum geology include boosting the breakthrough of petroleum exploration in Cenozoic in North China basin; supervising the publication of the Atlas of Petroleum Geology in People's Republic of China; initiating the three-series division of the continental Cretaceous in China, and thus directing the classification of Cretaceous sedimentation types and selection of prospective areas; promoting the scientific research, reconnaissance and exploration of natural gas, including coal-derived or humic gas, resulting in large progress to be made in our natural gas exploration; participating the planning of our second round petroleum reconnaissance, under his guide large progresses have successively been made in major petroliferous provinces,such as Ordos basin, northwest Sichuan, Pearl River Mouth basin in northern South China Sea, shelf basin in East China Sea and northern Tarim basin. Academician Guan Shicong was adept in summarizing theories from practices. In his book "Marine-Facies, Terrestrial and Offshore Petroleum Geology in China", he proposed a composite mode of paleo-marine depositional environments in China, which consisted of 2 facies groups, 6 facies regions and 16 facies belts, and incisively forecasted the exploration potential of the marine formations. Since all the Meso-Cenozoic continental basins in China are of intraplate basins, he proposed a new principle for classification of Meso-Cenozoic continental sedimentary basins in China, and have effectively guided the petroleum exploration in continental basins in China.

Geological features and resource potentials of coalbed methane basins in China

Sun Wanlu, Chen Zhaoyou, Chen Xia, Wang Shuhua, Fu Xiaoyun

2005, 26(2):  141-146,154.  doi:10.11743/ogg20050202

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Coal basins in Chinese mainland are mainly distributed in Tarim-North China plate, South China plate and the relatively stable landmasses and land blocks in Junggar-Xing'an active belt, and have mainly been formed in Permo-Carboniferous, Late Triassic-Early Cretaceous and Tertiary. They can be divided into intraplate cratonic basins and intracontinental rift-depression basins according to their locations in tectonic domain and sedimentary structural features. Reservoiring of coalbed methane in coal basins have been controlled by the following factors:(1) formation, distribution and quality of coals have been controlled by palaeoclimate, fossil plant, palaeogeography, palaeostructure and depositional environment; (2) tectonic deformation has controlled directly the entire sealing conditions of the basins and influenced the burial depth of coal beds and filtration properties of coal reservoirs; (3) degree of metamorphism has influenced both the amount of coalbed methane generated from coal and the filtration properties of coal beds; (4) sealing and hydrodynamic conditions would have determined the preservation of coalbed methane reservoirs. The prospective coalbed methane resources in China have been estimated to be 20TCM (trillion cubic meters).

Genesis of subsidence-accumulation centre in Quemocuo area of Qiangtang basin:caving-in subsidence with thermal attenuation

Liu Chiyang, Yang Xingke, Ren Zhanli, Zheng Menglin, Lai Shaocong

2005, 26(2):  147-154.  doi:10.11743/ogg20050203

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Jurassic is very thick and has a complete sequences in Quemocuo area, northeastern Qiangtang basin.The Quemocuo Formation and Xueshan Formation, the earliest and latest Jurassic deposits,both presently have a remaining thickness of over 1300m, representing the apparent local subsidence-accumulation centers of the times in the basin. These two subsidence-accumulation centers have very similar development background and evolution process, i.e. there are the evidences of early-stage thermal-magmatic activity and relevant uplifting backgrounds, subsequently, the uplifted areas where the early deposits being thin or even denuded have subsided rapidly and accumulated very thick deposits. The special phenomena that uplifts and depressions occur successively in time and are superimposed vertically are characteristic of structures having been formed by thermal activity.This unique feature shows that Quemocuo area has experienced two geologic processes:(1) humping up of deep thermal-magmatic activity, magmatic eruption, and uplifting and denudation of superficial and shallow crust in early stage; (2) thermal attenuation and cooling down at depth and caving in and depression of superficial and shallow crust in late stage. The deep structures revealed by aeromagnetic survey and magnetotelluric depth sounding data acquired in recent years verify the existence of this thermal subsidence structure. The vitrinite reflectance(R₀)of Upper Jurassic Xueshan Formation ranges from 1.63%to 1.83%, providing evidences for the Mesozoic thermal anomaly. The thermal attenuation and accompanying magmatic activities had lasted till Late Cretaceous-Early Tertiary. Later, this area was uplifted and cooled down.

Three stages of tectonic movements in formation of petroliferous basins in China

Xu Xuhui, Gao Changlin, Huang Zeguang, Fan Xiaolin, Liu Guangxiang, et al

2005, 26(2):  155-162.  doi:10.11743/ogg20050204

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China's mainland, with complex and uneven components, is a composite continent, contributed by convergence of several small landmasses with different basement structures and different ages. Formation and distribution of basins in China have been controlled by tectonic settings and changes of basin-forming systems. Basins in China have been formed in 3 stages, including the formation of Paleo-China, Pal-Asia and Neo-Asia. Being affected by pericontinent-and intracontinent-dominant tectonic-thermal systems, Paleozoic basins have been formed in Paleo-China/Pal-Asia tectonic settings, and Meso-Cenozoic basins have been formed in Neo-Asia tectonic setting. The Meso-Cenozoic basins have been developed in the interior of converged and condensed continent, and have experienced 3 tectonic changes:the first one occurred during Late Triassic-Early Cretaceous, the second during Late Cretaceous-Eocene and Oligocene, and the third during Oligocene/Neogene through to the present. The Paleozoic basins have been superimposed and reformed by the Meso-Cenozoic basins, resulting in complex basin structures.

Two aspects of natural gas resources in China and their development strategy

Zhang Kang

2005, 26(2):  163-167.  doi:10.11743/ogg20050205

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Natural gas industry in China has entered a fast-developing stage, and China will soon become a large gas producer. However, the abundance of natural gas resources in China is relatively low, thus large amount of natural gas still need to be imported in the future. Our gas industry is faced with some "quality"problems. Gas fields in China are generally characterized by relatively small reserves, low abundance, low individual-well productivity and rapid decline of production. In addition, the foundation of our gas industry is weak and most of the gas fields are far from the economically developed areas, which need building very long pipelines for transportation. Thus both wellhead price and transportation cost are high, resulting in a relatively high end-user price, which would influence its competitive capacity in the energy market. Therefore, when formulating development strategy of our gas industry, study of integrated development should be strengthened, and importance should be attached to progressive development while exploring the low-grade gas resources, to comprehensive planning of the upstream and downstream sectors, to overall planning of pipe network construction, to adjustment of the distribution of industrial users, and to the development of LNG.

Thoughts on study of halo-source correlation:fundamental principles of geochemical exploration

Gong Weiqi, Yao Junmei

2005, 26(2):  168-176.  doi:10.11743/ogg20050206

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GC-MS,UV and TSF have been used to measure traces of hydrocarbons (<10^-6)in shallow and surface layers in various areas, such as Lishu of Songliao, Ordos, western Sichuan, Tianchang of Northern Jiangsu and Yakela of Northern Tarim. Vertical micro-migrations of hydrocarbons from subsurface sources have thus been proved, which would result in halo-source relationship of dispersion haloes over the sources. There will be no exception even if the reservoirs are buried at a depth of over 5000m and there are tight seals. Presently, study of the basic principles of geochemical exploration is relatively weak. In view of this situation, we should begin with the observation of geochemical fields at depth, and determine the traces of micro-percolation of hydrocarbons in combination with fine seismic and geologic data, so as to verify different mechanism hypotheses. At the same time, we should also pay attention to dynamic observation of subsurface hydrocarbon micro-percolation, strengthen study of fabric geochemical field and genesis of geochemical anomalies, and speed up the simulation tests of relevant mechanisms.

Thermal evolution pattern of organic matter abundance in various marine source rocks

Qin Jianzhong, Jin Juchang, Liu Baoquan

2005, 26(2):  177-184.  doi:10.11743/ogg20050207

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Both simulation experiment on source rocks performed under watered, heated and pressured conditions and measurement of natural evolution sections show that thermal evolution of organic matter abundance in various marine source rocks can be divided into 3 stages, i.e. immature-low mature stage, mature stage and high mature-overmature stage. In immature-low mature stage (R₀<0.8%),TOC and hydrocarbon generating potential change insignificantly with increasing maturity. In mid-late mature stage (R₀= 0.8%-1.3%), TOC and hydrocarbon generating potential decrease progressively with increasing maturity, simply due to the persistent generation and expulsion of large amount of hydrocarbons. While in high mature-overmature stage, TOC varies insignificantly again with increasing maturity. The abundance of organic matter lowers significantly from immature-low mature stage to high mature stage, thus the original TOC should be restituted. Comparison of different types of source rock shows that the restitution coefficient is related to hydrocarbon-generating and-expulsing potentials, kerogen types, maturity and TOC, while it has little correlation with lithologies.

Relationship between Sino-Korean orogenic belt traversing Yellow Sea and basin evolution and hydrocarbon generation in North and South Yellow Sea basins

Cai Qianzhong

2005, 26(2):  185-192,196.  doi:10.11743/ogg20050208

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Yellow Sea area, located between the margin of China's mainland and the oceanic crust of the Western Pacific Ocean, has transitional crustal structure. Being controlled by the surrounding tectonics, the basement in North Yellow Sea basin is of the North China landmass, while that in South Yellow Sea basin is of the Lower Yangtze landmass, as a result, the crustal structure is very complicated. Based on the strike-slip movement of Tancheng-Lujiang fracture, massive northward overthrusting of North Jiangsu plate along the fracture and the cut-in of Shandong-Jiangsu ultra-high pressured metamorphic zone, and in combination with stratigraphic paleontologic study and dating of rock to be 220～230 Ma, it is believed that North China landmass would have collided with the Lower Yangtze landmass in early Triassic, leading to the formation of Sino-Korean orogenic belt traversing the middle of Yellow Sea. The NEE trending Sino-Korean orogenic belt, with a wedge shape being wide in the west and narrow in the east, is composed of Sujiao orogenic zone, Qianliyan uplift zone and Linjinjiang orogenic zone. Since Middle Jurassic, the re-uplifting of the orogenic belt resulted in the rifting and subsiding of the North and South Yellow Sea basins and deposition of Upper Jurassic and Cretaceous strata. There are two petroleum systems in North Yellow Sea basin. The first one, with the Upper Jurassic deep or semi-deep lacustrine sediment to be the major source rocks and the Upper Jurassic and Lower Cretaceous sandstones and sandy conglomerate to be the good reservoirs, has been verified by well producing wells,such as the.606 well. While the second one, with the Tertiary paludal coal measures to be the source rocks and the Tertiary siliceous clastic rocks to be the reservoirs, has gas potentials. South Yellow Sea basin can further be subdivided into northern depression, middle uplift zone and southern depression. In the southern and northern depressions, Lower Tertiary Funing and Dainan Formations are the major source rocks, and the Taizhou and Pukou formations are the possible source rocks. The Mesozoic and Lower Tertiary are absent in the middle uplift zone, since it has long been uplifting. Exploration of the Paleozoic should be strengthened in the middle uplift zone, where prolific gas reservoirs are expected to be discovered in Silurian-Devonian.

Renew exploration concept and open up frontiers in deep strata

Zhang Zhiyi

2005, 26(2):  193-196.  doi:10.11743/ogg20050209

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Source rock, a concept with many uncertainties, has confined the thoughts of explorationists for a long time. V.B.Porfiriev, the late Academician of Ukraine Academy of Sciences, proposed a theory of deep origin of hydrocarbons, i.e. generation of hydrocarbons has been related to activities of the upper mantle. At the end of Tertiary, hydrocarbons migrated vertically upward from the upper mantle along large fracture belts and accumulated in the porous-fractured reservoirs in the basement and sedimentary cover. Deep and ultra-deep drilling in Gulf of Mexico has verified that oil pool can occur in reservoir up to a depth of 6 885 m. It is justified to believe that should fractured zones exist in the deep crystalline and metamorphic rocks below the basin's basement, they would be the petroleum occurrences. Therefore, it would be possible to open up frontiers of petroleum exploration through deep drilling.

Meso-Cenozoic tectonic setting and evolution of East China Sea shelf basin

Zheng Qiugen, Zhou Zuyi, Cai Liguo, Lu Yongde, Cao Qinggu

2005, 26(2):  197-201.  doi:10.11743/ogg20050210

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Based on distribution of Mesozoic in East China Sea and magmatic-tectonic events in the eastern Fujian and Zhejiang provinces, Kula-Pacific plate would have relatively strong subduction toward China's mainland during Jurassic-Early Cretaceous, thus East China Sea and the area to the south should be of fore-arc basin. During late Late Cretaceous-Eocene, volcanic island arc moved eastward and the East China Sea shelf basin was turned into a back-arc basin. The centers of fault subsidence were located in Changjiang and Oujiang sags in the western part of the shelf basin during Palaeocene, and they moved eastward during Eocene and consisted mainly of the Xihu sag in the eastern part of the shelf basin. East China Sea shelf basin was downwarped in Oligocene, due to the change of subduction direction of Pacific plate and the effect of Philippine Sea plate, and the center of depression was mainly located in the eastern part. Okinawa ocean trough and Ryukyu island arc were formed in late Miocene. During late Miocene (approx. 6 Ma), Luzon island arc collided with China's mainland in Taiwan area, resulting in the emergence of Taiwan Island, and the formation of the present features of Taixi(or West Taiwan) basin.

Differences between formation conditions of Ordovician karstic reservoirs in Tazhong and Tahe areas

Yan Xiangbin, Li Tiejun, Zhang Tao, Li Guorong, Jin Xiaohui, Ma Xiaojuan

2005, 26(2):  202-207.  doi:10.11743/ogg20050211

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Comparative study shows that Ordovician karstic reservoirs in Tazhong and Tahe are quite different. In Tazhong, Ordovician dolomite reservoirs are characterized by small karst vugs, and limestone reservoirs are characterized by limited karst caves. While the karst cavernous reservoirs in Tahe are characterized by superimposition of multiple series of strata and continuous distribution in a large area. The main factors that have caused the differences of Ordovician karstic reservoirs in Tazhong and Tahe are tectonic evolution, lithofacies palaeogeography and dissoluble rock types. In Middle Caledonian, thrusting and folding were strong and well developed, dissoluble dolomites or limestones were dispersedly outcropped in narrow strips, and karst slopes were developed limitedly in Tazhong area; while tectonic movement in Tahe area was weak at that time. In Early Hercynian, Tahe area was wholly and largely uplifted, resulting in formations being strongly denuded and leveled, dissoluble limestone strata being flatly outcropped in large area, and karst slopes being well developed. Meteoric water flowed along the existing fracture systems and dissolved and reconstructed them in tubular flow, resulting in large cave systems. Several sets of cavernous reservoirs are distributed in large areas, due to multiple series of strata being superimposed and interconnected. However, tectonic movement in Tazhong was relatively moderate in Early Hercynian. Therefore, Tazhong area was dominated by Caledonian karst, while Tahe area was dominated by Hercynian karst.

Chronological characteristics of Upper Triassic reservoirs in western Sichuan depression

Yang Keming, Ye Jun, Lü Zhengxiang

2005, 26(2):  208-213.  doi:10.11743/ogg20050212

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The Upper Triassic in western Sichuan depression can be divided into 2 source-reservoir-cap rock combinations. The peak of hydrocarbon generation and expulsion in the lower combination occurred during middle-late stages of Late Triassic; while that in the upper combination occurred in Late Jurassic. Both mechanical compaction and infilling of authigenic minerals would have contributed to the tightening of reservoirs in Xujiahe Fm, which occurred at the end of the Middle Jurassic Upper Shaximiao through to Late Cretaceous. Analysis of fluid inclusions indicates that gas reservoirs in the 2^nd member of Xujiahe Fm were charged mainly at the end of the deposition of the 4^th member of Xujiahe Fm through to the end of Middle Jurassic. Multiple phases of tectonic movements resulted in polyphase traps in western Sichuan depression, of which the large Yanshanian palaeohigh had the best timing with hydrocarbon migration and accumulation. Based on the stages of hydrocarbon generation and expulsion, tightening of reservoirs, fluid charging and trap formation, it can be determined that the main reservoiring stage in the Upper Triassic in western Sichuan depression would be from middle-late Indosinian to middle-late Yanshanian.

Compound structures and hydrocarbons in western Sichuan depression

Deng Kangling, Yu Fulin

2005, 26(2):  214-219.  doi:10.11743/ogg20050213

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Compound structures, such as coaxial superimposed, cross-over and mitre types, are common in western Sichuan depression as a result of multistage tectonic events. They have been formed early, thus would have been favorable for timely migration and accumulation of gas prior to the tightening of Xujiahe Formation sandstones. Compounding of structures would be favorable for the formation of crush structures, which would have improved the percolating conditions of the reservoirs and productivity of gas wells, and would have established communication between deep source rocks and shallow reservoirs, leading to the formation of gas pools far from their sources. The large fracture in western Sichuan depression has been formed as a result of multistage tectonic events and has led to the destruction of gas pools. Medium and small gas pools might have been preserved in areas far from the large fracture, due to the inhomogeneity of the reservoirs.

Formation mechanism of secondary dissolved pores in arcose

Li Wenguo, Zhang Xiaopeng, Zhong Yumei

2005, 26(2):  220-223,229.  doi:10.11743/ogg20050214

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In acidic aqueous media, feldspar minerals can be dissolved to some extents, leading to the formation of secondary pores. Secondary porosity can be quantitatively estimated based on the composition and physicochemical properties of the original and secondary minerals. Secondary porosity formed by dissolution of K-feldspar can be as high as 11.91%, while that of calcium feldspar is the lowest, being only 0.27%, and that of sodium feldspar and andesine range between the former two. Some of the CO₂ needed for dissolving feldspar might have been sourced from meteoric water and/or dissolved from the air when water got in touch with atmospheric air, while the others might have been the products of decomposition of organic matter during generation of hydrocarbons.

Relationship between palaeostructure and gas reservoirs in Xujiahe Formation in western Sichuan depression

Cao Lie, An Fengshan Wang Xin

2005, 26(2):  224-229.  doi:10.11743/ogg20050215

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According to the geologic conditions of Xujiahe Formation in western Sichuan depression to be characterized by super-deep, overpressure, super-tight and super-late structures, systematic analysis of hydrocarbon generation history, pore evolution history and structural evolution history of the known Zhongba, Hexingchang and Pingluoba gas reservoirs and analysis of both positive and negative exploration cases have been made.It has been clear that palaeostructures have acted as the basis of gas accumulation. Yanshanian palaeohigh zone determined the distribution of gas reservoirs, characterized by common early reservoiring, and palaeostructural-diagenetic traps to be the main types of hydrocarbon traps in the study area. Gas reservoirs in Xujiahe Fm in western Sichuan depression have experienced several evolution stages, including conventional trapping in the early stage, suspension in middle period and reconstruction in late stage. Majing-Deyang area, where there is Yanshanian palaeohigh, has experienced similar evolution process, thus it might be a prospective play.

Discussion on characteristics and reservoiring mechanism of deep basin gas in Upper Paleozoic in Ordos basin

Ma Xinhua

2005, 26(2):  230-236.  doi:10.11743/ogg20050216

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He 8 and Shan 2 plays in the study area have the characteristics of and conditions for accumulation of deep basin gas. The reservoirs are characterized by high compactibility, sporadic water production in gas-bearing area and strong compartmentalization of gas reservoir pressure, mainly due to continental sedimentary sequence and later reconstruction of gas reservoirs. Geologic analysis and physical modelling show that sandbodies have regional connectivity (along) strike, thus migration and accumulation processes of gas displacing water might occur in reservoiring conditions. A development stage and a reconstruction stage of deep basin gas can be divided at the end of Early Cretaceous. Reservoir pressure evolved from overpressure to underpressure in the reservoiring process. The main factors that caused the pressure drops in different areas are not the same. In Suligemiao area, it is mainly caused by the enlargement of dissolution pores in reservoirs, and temperature drop also has certain influences. While in Yulin and Shenmu-Mizhi areas in eastern Ordos Basin, it is mainly caused by the uplifting and temperature drop.A specific reservoiring pattern is presented based on comprehensive analysis of reservoiring features and process.

Geochemical characteristics of Cretaceous sandstone-mudstone and its importance to tectonics in Zhoukou basin

Gao Changlin, Huang Zeguang, Zhang Yuzhen

2005, 26(2):  237-241.  doi:10.11743/ogg20050217

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The prototype of Zhoukou Cretaceous basin should be of foredeep basin. In the Q-F-L graph, the plotted points of quartz, feldspar and lithoclast contents of Cretaceous sandstone-mudstone cored from wells are mainly located in foreland basin area. While the plotted points of the major compounds in Cretaceous sand-shale are mainly located in active continental margin area. The total contents of rare earth elements and the ratio of light/heavy rare earth elements change insignificantly, similar to the characteristics of sandstone and siltstone in Russian Platform. Therefore, it is believed that Cretaceous sediments in Zhoukou basin might have been sourced from Qinling-Dabie orogenic zone and the lithogenous materials come from the source area might have been thoroughly blended.

3-D seismic survey of shallow reservoirs in Xinzhuang area, Biyang depression

Qiu Ronghua, Sun Yaohua, Zhang Yonghua, Tian Xiaomin, Zhu Jingxiu

2005, 26(2):  242-245,262.  doi:10.11743/ogg20050218

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Reservoirs in Xinzhuang area, Biyang depression, are characterized by shallow burial depth, large thickness and high enrichment, and are mainly of fault-nose and fault-block types. In view of the shallow burial depth of reservoirs and complexity of fault blocks, 3D seismic survey method that can well preserve reflected signals has been applied in Xinzhuang area. In seismic acquisition, a fasciculate observation system with short offset distance and small bin has been used. In seismic processing, stress has been put on velocity analysis and pre-stack migration. In seismic interpretation, various functions of interactive system have been integrated to identify faults and to ascertain fault blocks. A lot of oil-bearing traps have been discovered by exploration wells positioned on the basis of the interpretation results.

Faulted structures and hydrocarbon migration in central uplift belt of Dongying Depression

Ma Lijuan, Zheng Herong, Xie Xinong

2005, 26(2):  246-251.  doi:10.11743/ogg20050219

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Central uplift belt of Dongying depression has been formed as a result of joint action of the extensional fault-flexure folding of Chennan fault and diapirism of plastic salt-mud layers controlled by regional and local structural stress fields. Development levels and combination features of structures in the central uplift belt are spatially quite different, due to differential actions of various factors, such as distribution of salt-mud layers, sedimentary features when the faults were active and regional tectonic stress field. The central uplift belt can be divided into 3 structural zones, i.e. Xinzhen, Dongying and Liangjialou-Xianhezhuang structural zones. Distributions of oil and gas are closely related to faulting in the central uplift belt:(1) hydrocarbons have mainly been accumulated in shallow reservoirs as secondary pools when the strength of faulting changed from weak to strong; (2) hydrocarbons have mainly been accumulated in deep reservoirs as primary pools when the strength of faulting changed from strong to weak; (3) hydrocarbons have been accumulated both in shallow and deep reservoirs constitute complex oil-gas accumulation zone with multiple oil-bearing series and various types of oil pools when the strength of faulting changed first from weak to strong and then from strong to weak.

Analysis of evolution of Meso-Cenozoic basins in southern North China

Huang Zeguang, Gao Changlin, Ji Rangshou

2005, 26(2):  252-256.  doi:10.11743/ogg20050220

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The Late Jurassic-Early Cretaceous volcanic rocks in Dabie orogenic belt are alkali rocks with high potassium content. The corresponding tectonic setting was not a subduction zone, but had certain relationship to plate subduction. The Tancheng-Lujiang fracture zone was characterized by its intenso-wrench or dextral strike-slip movement during Late Jurassic-Early Cretaceous. The Meso-Cenozoic basins in southern North China have significant differences, due to their specific tectonic settings. Taking Pingyu-Bangbu uplift as a boundary, the southern basins, located in the thrust front of Dabie orogenic belt, such as Hefei-Xinyang basin, are triple overlapping basins, which are composed of foreland basin prototype as a result of compressional orogenesis, strike-slip basin prototype as a result of tenso-wrench movement, and extensional counter-inclined normal fault and strike-slip faulted basin prototype. While the northern basins, located in relatively stable landmass, are multiple overlapping basins, which are composed of compressional foreland basin-intracontinental depression prototype, strike-slip basin prototype, depression,transtensional and faulted basin prototype as a result of weak compression, and depression basin prototype as a result of mass subsidence.

Relationship between transfer structures and hydrocarbons in Baiyinchagan depression

Ku Guozheng, Zhang Fangdong, Deng Yixun, Li Xi'ai, Wang Jingyun, Liu Jinzhong

2005, 26(2):  257-262.  doi:10.11743/ogg20050221

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During the evolution of Baiyinchagan depression, various types of transfer structural accommodation systems have been formed in different parts of the extensional structure, due to the elevation and subsidence of the basement and uneven faulting. Maohu swell in Baiyinchagan depression is a large transfer structural zone, which consists of two synthetic oblique accommodation zones and one strike-paralleled accommodation zone. The structural accommodation zones in the western sag can be divided into 4 types, including antithetic anticline accommodation zone, synthetic transverse accommodation zone, synthetic oblique accommodation zone and strike-paralleled accommodation zone. Exploration practices show that there are well developed structural, lithological and overlapping unconformity traps in the Xilinhaole, Darqinan, Darqidong and Wongte accommodation zones and their adjacent areas in southern part of the western sag, and they have long been in the major direction of hydrocarbon migration. Therefore, they are favorable for the accumulation and enrichment of hydrocarbons.