OIL&GAS GEOLOGY-2003, Volume 24 Issue 1

CAUSATION OF PARTLY REVERSED ORDERS OF δ¹³ C IN BIOGENIC ALKANE GAS IN CHINA

Dai Jinxing, Xia Xinyu, Qin Shengfei, Zhao Jingzhou

2003, 24(1): 1-6,11. doi:10.11743/ogg20030101

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The δ¹³C values change in a regular manner with the increase of hydrocarbon gas molecular weight, i.e. change in normal order or reverse order.The normal order is δ¹³C₁<δ¹³C₂<δ¹³C₃<δ¹³C₄,and the reverse order is δ¹³C₁> δ¹³C₂>δ¹³C₃>δ¹³C₄.Partly reversed order is also common in gas samples from different basins in China,such phenomenon can be attributed to one or several of the following reasons:(a)Mixing of biogenic gas and abiogenic gas;(b)Mixing of gases from sapropelic sources and humic sources;(c)Mixing of gases from two source rock intervals of the same type but of different maturity;(d)Mixing of gases from one source rock interval of varying maturity.

DISCUSSION ON RECOVERABLE OIL RESOURCES IN CHINA

Zhang Kang

2003, 24(1): 7-11. doi:10.11743/ogg20030102

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There is great difference between the petroleum resources used in China and the concept of resources commonly used in the world, which would easily result in confusion and misunderstanding. So, we especially regard the resources used in China as geological resources, which can be called recoverable resources after it has been revised with its economic availability and predicted recovery.It can then be approximately correlated with the resources in the world. Based on the composite volume of proved reserves and geological resources in 2000 to be 1035?10⁸t, and the recoverable resources is calculated to be 116.1?10⁸t,correspondingly, the degree of resources to be proved is 52.2%. After averaging the 16 values independently estimated by different geological experts in different periods, the recoverable resources is about 132.5?10⁸t. Being compared to the equivalent values, the recoverable oil resources in China is slightly higher than that of natural gas.For both resources and undiscovered oil recoverable resources, eastern China ranks first, and the second would be north-western China and the continental shelf.

CHARACTERISTICS OF MESOZOIC VOLCANIC RESERVOIRS IN SONGLIAO BASIN

Song Weihai, Wang Pujun, Zhang Xingzhou, Meng Qi'an, Shan Xuanlong, Cheng Rihui

2003, 24(1): 12-17. doi:10.11743/ogg20030103

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The Mesozoic volcanic reservoirs in Songliao basin formed in the Late Jurassic to Early Cretaceous volcanic-sedimentary sequences. The vertical or lateral contacts between the deep lacustrine argillaceous rocks and volcanic rocks are the key factors of the formation of volcanic reservoirs during the volcanic-fault depression period—basin forming. Rock types of volcanic reservoirs include mainly lava and pyroclastic rock.The major volcanic reservoirs are mainly in the effusive facies, and the best reservoir belts are in the gas cavity belts on top and at base of the effusive facies. The reservoir spaces can be divided into primary pores, secondary pores and fissures. The volcanic reservoirs are mainly controlled by both NNE and nearly EW regional faults, most of them occur in active regional fault zones, basement uplifts or tectonic zones.

RELATIONSHIP BETWEEN VOLCANIC FACIES AND VOLCANIC RESERVOIRS IN SONGLIAO BASIN

Wang Pujun, Chen Shumin, Liu Wanzhu, Shan Xuanlong, Cheng Rihui, Zhang Yan, Wu Haibo, Qi Jingshun

2003, 24(1): 18-23,27. doi:10.11743/ogg20030104

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Based on the study of cores, well cuttings, and outcrop sections, the facies of volcanic rocks can be divided into 4 types and 12 sub-facies. Pores and fissures are the two major types of reservoir spaces in volcanic rocks in Xujiaweizi fault-depression. The types of reservoir space in volcanic reservoirs have been found to be controlled by the facies. The volcanic reservoirs found in various facies belts have quite different pores and fissures and their assemblages. Gas cavities, fissures in rhyolitic lamination, and joint fissures have been identified mainly in eruption-overflow facies. The main pore-type identified in explosive facies is intergranular pore; and inter-breccia pore and primary fracture are dominant in extrusive facies.Joint fissures and various primary fractures are mainly developed in volcanic conduit facies.It is found that “unconsolidated formation” often distributes at the base of each cooling unit in explosive explosive facies,which might be resulted from fast covering and conservation of the weathered crusts of the original basement rocks or unclinkered drifting clasts. A large “unconsolidated bodies in rock-dome” can often be found in the inner belt sub-facies of extrusive facies, which are actually of large accumulation bodies of perlite balls. Special attention should be paid to looking for these two-type reservoirs in the intermediate-acidic volcanic rock area. The major tectoclase in this area is a set of conjugated, high-angle (fault plane with dip angle of 50°～60°), NNE and NNW strike, and shear or compressive-shear fractures, which constitute the main migration pathway of oil & gas.

OCCURRENCES OF VOLCANIC ROCKS IN XUJIAWEIZI FAULT-DEPRESSION AND THEIR SIGNIFICANCE

Cheng Rihui, Liu Wanzhu, Shan Xuanlong, Chen Shuming, Qu Yongbao

2003, 24(1): 24-27. doi:10.11743/ogg20030105

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The volcanic rocks in Xujiaweizi fault-depression, Songliao basin,was mainly erupted in Late Jurassic to Early Cretaceous.Their occurences are characterized by a certain geometric pattern.On the basis of the structural position of volcanic eruption and the occurrences in the basin, three types of eruption have been identified, including eruption on the upthrown side of fault, along fracture belt and on downthrown side. Different occurrences are often corresponding to different basin structures. The volcanic rocks occurring along fault plane would transit gradually to sublacustrine fan—turbidite fan; the volcanic rocks occurring on the upthrown side of fault would distribute in the manner of alternating beds of volcanic rocks and sandstones; the volcanic rocks occurring on the downthrown side have mostly been covered by fine grain sediments.

CHARACTERISTICS OF DEEP VOLCANIC RESERVOIRS IN NORTHERN SONGLI AO BASIN

Liu Wanzhu, Wang Pujun, Men Guangtian, Bian Weihua, Yin Xiuzhen, Xu Liqun

2003, 24(1): 28-31. doi:10.11743/ogg20030106

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Deep volcanic reservoirs of Songliao basin have mainly been found in Huoshiling and Yingcheng Fms..The eruptive and overflow facies have better reservoir capacity, commonly with the porosity of 6.3%～10.8% and permeability of about 0.55×10^-3 ～122.0×10^-3 μm².The reservoir capacity of volcanic rocks has largely been affected by tectonism,solution and fluid activity.There are lots of fractures in volcanic rock due to tectonic activity during the volcanic-fault-depression period in Songliao basin,which would enhance the reservoir capacity.The eruptive tuffaceous volcanic has been mainly changed by leaching, and become loose and porous,with the porosity to be increased to over 15%.Fluid flow has double effects on reservoir capacity of volcanic rock, reservoir capacity would be reduced by cementation and filling of new minerals,but on the other hand, porosity would be increased by alteration and solution.These should,therefore, be studied separately by stages and periods.

EPISODIC RESERVOIRING FEATURES OF EASTERN SAG IN LIAOHE BASIN

Chen Zhenyan, Wu Wenzhu

2003, 24(1): 32-35. doi:10.11743/ogg20030107

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The testing results of fluid inclusion indicate that there were three charging stages of the oil and gas reservoirs in the eastern sag of Liaohe basin. The early stage (36 Ma) is equivalent to the deposition of the first member of Shahejie Formation to early Dongying; the middle stage (24～24 Ma) is corresponding to middle-late Dongying; and the late stage corresponds to Neogene up to the present time. The episodic and multiphase charging result in the heterogeneity of fluid properties both laterally and vertically.The deep crude in Oulituozi area has lower maturity than that in the shallow part, that is a phenomenon of reversed maturity. However, the crude maturity in the higher part of high horst zone in Ciyutuo area is higher than that in the relatively low position in Niuqing area. It is then suggested that exploration activity might be launched to enhance success ratio by using this feature.

CHARACTERISTICS OF PYROLITH RESERVOIRS IN BEIPU AREA, NANPU SAG

Zhou Haimin, Ma Qian

2003, 24(1): 36-38. doi:10.11743/ogg20030108

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Four sets of pyrolith reservoir assemblages have been identified in Beipu area, western Nanpu sag,Huanghua depression.The main pyrolith types include flood basalt and eruptive pyroclastic rocks, and the reservoir spaces are composed of fissures and intergranular pores. Drilling and logging results indicate that there are abundant fissures and pores in tuff on top and bottom of thick basalt in the 2nd and 3rd members of Shahejie Fm., respectively, which will have relatively good exploration potential. Additionally, the sandstones above and below the pyrolith,being affected by magmatic activity, the poroperm characteristics would have been improved.It is,therefore, suggested that the explorer should pay much attention to the sandstones.

RELATIONSHIP BETWEEN TERTIARY SEQUENCE STRATIGRAPHY AND OIL RESERVOIRING IN NANPU DEPRESSION

Dong Yuexia, Zhou Haimin, Xia Wenchen

2003, 24(1): 39-41,49. doi:10.11743/ogg20030109

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According to the genetic sequence interfaces and regional tectonic movement,Tertiary strata in Nanpu depression can be divided into 7 super-sequences,missing only the 2nd super-sequence by comparison with other basins in Bohai Gulf. Each of these super-sequences generally constitutes a complete source-reservoir assemblage.The deep lacustrine mudstone in the middle sequence set is a relatively good source rock, and the wedge-shaped, coarse-grain sedimentary system in the lower sequence set is a good reservoir rock. So, the most prospective position for deep hydrocarbon reservoir exploration might be the part of coarse-grain deposition system in the lower position,which is extending to the central part of the basin.

PORE STRUCTURE AND OIL DISPLACEMENT EFFICIENCY IN PANHE FAULT-BLOCK AREA

Xiong Min, Wang Qintian

2003, 24(1): 42-44,54. doi:10.11743/ogg20030110

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Panhe fault-block area is located in the western part of central uplift zone in Huimin sag.The pore structure of reservoir in the 3rd member of Shahejie formation can be divided into four types. The reservoir with super-high permeability, super-large pore and coarse throat pore structure has the highest oil displacement efficiency during the high water-cut stage; the simulation test can be as high as 70%～90%.However,the test run in actual rock sample, the oil displacement efficiency seem to be reduced (40%～75%),due to the non-homogeneous structure. The reservoir with high permeability, large pore and coarse throat pore structure has high oil displacement efficiency, which is usually 60%～80%. The reservoir with medium permeability, large pore and medium throat pore structure has relatively low oil displacement efficiency of about 40%～60%; and the reservoir with low-permeability, medium pore and fine throat has the lowest oil displacement efficiency, 30%～50%.However,the pore system in the reservoir does not consist of only one of the above-mentioned 4 pore structures, it is exactly the composition of several types of pore structures.

HYDROCARBON RESERVOIRING CHARACTERISTICS IN BAIMIAO STRUCTURE

Zhang Hongan, Li Jidong

2003, 24(1): 45-49. doi:10.11743/ogg20030111

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hydrocarbon-bearing sequences have been found in Baimiao structure, located in the central part of Lanliao fault in Dongpu depression. According to the comprehensive analysis of authigenic illite dating and fluid inclusion methods,the reservoiring in Baimiao structure can be divided into 4 stages: the first stage is about in 38 Ma, corresponding to the deposition of 3rd member of Shahejie Formation; as a result of the strong tectonic movement, oil and gas reservoirs would be hard to preserve, so this stage would be of no significance for reservoiring of oil and gas.The second stage is in 28～31.4 Ma, equivalent to the deposition of Dongying formation, which is similar to the first stage.The third stage is about in 25.4～20.4 Ma, relative to the elevation-denudation period after deposition of Dongying formation, the strength of fault movement becomes weak with the pressure decreasing, which is favorable to the reservoiring of oil and gas.The fourth stage is in 2 Ma, which is the readjustment and redistribution period of oil & gas reservoirs.The formation of oil and gas reservoirs in Baimiao structure is closely related to active strength of Lanliao fault. With increasing the active strength, fluid pressure would become higher and higher, and even exceed the rupture strength of rocks; as a result, oil,gas and water would then be expelled in mixed phase; and when temperature and pressure decrease, oil,gas and water would be separated, the reservoirs would then be formed on the upper part of high-pressure system.Owing to this progress going round and round, a special three-storied pressure systems have been formed in Baimiao region.

FORMATION OF NON-TECTONIC FRACTURES IN MUDSTONES IN GULONG DEPRESSION

Ding Wenlong, Zhang Bowen, Li Taiming

2003, 24(1): 50-54. doi:10.11743/ogg20030112

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Gulong depression in Songliao basin is a major hydrocarbon generating area, where the mudstones have well- developed fractures and abnormally high fluid pressure. Some of these fracture reservoirs have produced commercial oil and gas. Drilling results reflect that the lateral distribution of these mudstone reservoirs in Cretaceous Qingshankou Formation is neither related directly to growth of faults, nor related to the fold curvature ; the vertical distribution of these mudstone fracture reservoirs is not corresponding to the stress in the formation, too. These features indicate that fractures would not be the result of tectonic force. After modeling geological processes concerning the sedimentary burial history and the fluid generation, it is concluded that these mudstone fractures in Gulong depression are non-tectonic fractures,including the shrinking rocks caused by clay mineral de-hydration and pressure boost fracturing caused by heating of hydrocarbon. And these fractures have continuously been developed and expanded further by fluid overpressuring during Mingshui period, and some new fractures have also been produced in this period.

RESERVOIRING PATTERNS OF OIL AND GAS IN THE DEEP LAYER OF BIYANG DEPRESSION

Luo Jiaqun

2003, 24(1): 55-57. doi:10.11743/ogg20030113

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The deep oil and gas pools develop mainly in the lower third member of Hetaoyuan Formation in the deep sag in southeastern Biyang Depression. There are two reservoiring patterns: Anpeng-Zhaowa type and Xia'ermen type. The former is characterized by three charging periods and the reservoirs have mainly been formed in the middle and late stages. The latter type of oil and gas pools have undergone the processes of formation-destruction-reformation. The early anticlinal oil and gas pools were formed during the deposition of the first member of Hetaoyuan formation and Liaozhuang formation, the pattern of the present oil and gas pools was not formed till the later stage of deposition of Shangsi formation, due to the reformation and destruction,caused by the tectonic movement in the later stage of Liaozhuang formation deposition. Except the above-mentioned two reservoiring patterns, probably there are also lithologic oil & gas pools in lenticular sandstones, as well as deep basin reservoirs.

DEEP BASIN GAS ACCUMULATION IN QIANLIYUAN DEPRESSION

Wang Xiulin, Zhang Hongbo, Zhang Xiaoyi, Wang Yunsuo, Duan Hongmei, Wang Yuxiao

2003, 24(1): 58-61. doi:10.11743/ogg20030114

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Being controlled by Lanliao fault on the margin, Qianliyuan depression continues developing to provide the necessary foundation of the formation of deep basin gas accumulations. Well-developed hydrocarbon source rocks occur in Lower Tertiary in the depression, which has high evolution degree and abundant gas source.Tight sand reservoirs with low-porosity and low-permeability develop in the 3rd and 4th sub-members of the third members, Shahejie Formation,which are favorable for the formation of deep basin gas accumulations.Gas accumulations, characterized by “inverted gas and water”, anomalous high-pressure, long gas-bearing interval and low production,as well as unrelated with structure,etc.,have been discovered around Qianliyuan depression. Dongpu depression is a typical “fault-sag” type deep basin gas among the non-marine fault-depression basins, and the slope zone surrounding the depression will be favorable target for exploration in the future.

COMPOSITE STYLES OF STRUCTURAL-LITHOLOGICTRAPS IN SHIWU RIFT, SOUTHERN SONGLIAO BASIN

Wu Jincai, Lan Suqing

2003, 24(1): 62-64. doi:10.11743/ogg20030115

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On the basis of the interrelationship of structure and lithology of the trap, the composite traps can be divided into 4 styles, including monoclinal-lithologic trap, anticlinal-lithologic trap, fault block-lithologic trap and nose-lithologic trap. After studying the data of the central structural belt in Shiwu rift,southern Songliao basin, it is found that there are several structural-lithologic composite traps,such as the structure to the west of SN85 well, the structure to the northern SN87 well and North Gujiazi structure. These structural-lothologic composite traps will be the favorable exploration targets in the future.

CHARACTERISTICS OF AUTHIGENIC CLAY MINERALS IN COARSE-GRAINED AND LOW PERMEABILITY RESERVOIRS IN COAL MEASURES AND ITS EFFECT ON RESERVIOR PROPERTY—AN EXAMPLE OF OIL RESERVOIR IN JURASSIC SANGONGHE FORMATION IN YANQI BASIN

Yao Guangqing, Sun Shangru

2003, 24(1): 65-69. doi:10.11743/ogg20030116

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The coarse-grained and low permeability sandstone reservoirs in Jurassic coal measures in west-central China is characterized by high content of authigenic clay minerals. Especially, the content of kaolinite is very high relative to other clay minerals. The study made in Yanqi basin shows that the total content of clay minerals and kaolinite content decreases with depth below the unconformity, but the content of illite and chlorite increases with depth. At same burial depth, the sandbodies with higher feldspar content and larger thickness in the main channel have more abundant kaolinite. The acidic fluid medium environment was the key factor controlling the formation of clay minerals in coal measure strata. The existence of abundant clay minerals has reduced the permeability and enhanced the sensibility of reservoir, and strongly affected the EOR efficiency in the oilfield.

INOZOAN,MAJOR REEF FRAME-BUILDING ORGANISMS IN LATE PERMIAN, HUNAN

Yang Zhiyuan, Liu Zuhan

2003, 24(1): 70-74. doi:10.11743/ogg20030117

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The late Permian reefs are distributed in Chengxian, Guiyang and Chenxi Counties in southern Hunan province. Reefs in Bangxian and Guiyang are patch reefs developed along Chengru shallow sea. Reefs in Chenxi are bioherms, undeveloped patch reefs. The reefs in both sites occur in the late Permian Changxing Formation. A lot of samples of fossils and rocks have been collected while surveying 8 reef composite sections in southern Hunan. We find that the most important frame-building organisms are calcisponges, just as other Permian reefs in southern China. By systematically researching Inozoans, one of the important frame-building calcisponges, it is thought that the water system and fibres might be important evidence in classification. Twelve species and 8 genera of Inozoans including one new species, one comparative species and one undefined species are found, and some species are newly classified.

RESERVOIR CHARACTERISTICS OF PALEOCAVE CARBONATES—A CASE STUDY OF ORDOVICIAN PALEOCAVE IN TAHE OILFIELD,TARIM BASIN

Xiao Yuru, He Fengyu, Sun Yimei

2003, 24(1): 75-80,86. doi:10.11743/ogg20030118

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Paleocave carbonate reservoirs are characterized by their heterogeneity,and they are very difficult to predict. For the sake of building a realistic geological model of the paleocave carbonate reservoir, correlation has been made with the paleocaves occurred in Wudaoban outcrop sections in Bachu area. The shape, size, structure, cave deposit, genesis and reservoir properties of the Ordovician paleocaves in Tahe oilfield, Tarim basin,have been studied on the basis of the theory of karst and the paleocave marks identified by means of drilling, logging, well logging, testing and seismic methods. The vertical and lateral heterogeneities of paleocave carbonate reservoir have also been discussed. Vertically, paleocave sediments can be divided into the top facies, filling facies and the lower sloughing facies. The top facies and the lower sloughing facies are quite favorable for hydrocarbon entrapment. But the development of multiple paleocaves have mainly been controlled by tectonic uplift and sea-level fluctuation. Ancestral structures, such as paleofault, paleodrainage system and paleokarst topography etc. have mainly been influencing the lateral heterogeneity of paleocave carbonate reservoirs, among which the paleokarst topography has the closest relation to lateral heterogeneity of paleocave carbonate reservoir. The study indicates that the relatively good paleocave carbonate reservoirs include the unfilled paleocave reservoirs and large paleocave-filling deposits—porous sandstone reservoirs.

CHARACTERISTICS OF STORM DEPOSITS IN UPPER TRIASSIC XUJIAHE FORMATION, SICHUAN BASIN

Li Huaqi, Jiang Zaixing, Xing Huanqing, Xian Benzhong

2003, 24(1): 81-86. doi:10.11743/ogg20030119

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Storm deposits has been found for the first time in the 2nd member of Xujiahe Formation ( Upper Triassic) in western Sichuan Basin.Based on the micro-facies of cores,the main types of tempestite sedimentary characteristics have been identified, including gutter cast, scouring surface, truncated structure, storm lag deposit, hummocky cross-stratification,convoluted laminations, V-shaped structures generated by wave. A detailed study of sedimentary structures and petrological features of storm deposits has been made, such as individual laminates,thickness of storm deposit, and so on. The storm deposits are characterized by their lithologic features, and storm sedimentary sequence are related to storm activity and similar to the typical Bouma sequence.The sedimentary environment of tempestites is discussed,and the storm sedimentary model is explored.

DAMAGES OF INJECTION WATER QUALITY TO RESERVOIRS IN TAIXING OILFIELD AND THEIR COUNTERMEASURES

Liu Bin, Yang Qi, Tan Shihai

2003, 24(1): 87-90,96. doi:10.11743/ogg20030120

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