2005 Vol. 11, No. 1

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PETROLEUM-FORMING CHARACTERISTICS OF COMPRESSIONAL SUPERIMPOSED BASINS IN NORTHWESTERN CHINA
KANG Yu-zhu
2005, 11(1): 1-10.
Abstract (150) PDF (320KB)(9)
Abstract:
The western region of China covers an area of 2.60 million km2, where more than 100 oil/gas fields have been found and there are very abundant oil/gas resources. Through several decades of research and exploration, the petroleum-forming characteristics of compressional superimposed basins in the region have been summarized, including polycyclic evolution, seven properties of tectonic deformation, poly-epochal hydrocarbon source rocks, several reservoir rock-cap rock combinations, four phases of accumulation formation, distinctive characteristics of oil/gas accumulations and characteristics of petroleum distribution.
NUMERICAL MODELING OF THE ACCUMULATION-FORMING HISTORY OF THE KONGXI BURIED HILL,BOHAI GULF BASIN
MENG Yuan-lin, WANG Yue-chuan, LUO Xian-ying, GAO Jian-jun, XIAO Li-hua, ZHOU Xin-gui, YIN Xiu-lan, WANG Zhi-guo
2005, 11(1): 11-18.
Abstract (208) PDF (340KB)(9)
Abstract:
A new numerical modeling system of the accumulation-forming history is established by numerical modeling of the essential elements of accumulation formation in carbonate rocks including source rocks, reservoir rocks, seal rocks, traps, primary migration and preservation,and the Kongxi buried hill tectonic belt in the Huanghua depression of the Bohai Gulf basin is used as an example to illustrate the application of this system. As the modeling results show, hydrocarbons were expelled from the Ordovician source rocks of the Kongxi buried hill tectonic belt in the Indosinian period and primary hydrocarbon accumulation began. The Yanshanian period was a main hydrocarbon generation stage and accumulation formation stage, when hydrocarbons were generated, expelled and accumulated in large quantity. Then primary hydrocarbon generation paused. In the Himalayan period, the tectonic belt was further buried and secondary hydrocarbon generation and tertiary hydrocarbon accumulation began. However, the amount of hydrocarbons generated during the secondary hydrocarbon generation was small. So the exploration for Lower Paleozoic primary oil/gas accumulations in the Huanghua depression should focus on the ancient structures that formed in the Indonesian and Yanshanian periods and were not destroyed by the late-stage tectonic movements.
FAULT SEAL MODEL OF THE CENTRAL UPLIFT, DONGYING DEPRESSION
XU Shou-yu, LI Xue-yan
2005, 11(1): 19-24,59.
Abstract (165) PDF (217KB)(9)
Abstract:
Fault systems in the Central uplift of the Dongying depression are complex. The fault sealing properties directly control the formation and distribution of the oil/gas accumulation as well as its size and type. Large oil/gas accumulations may form near a fault with good sealing properties, while small accumulations or even no accumulations occur near a fault with poor sealing properties. Take for example the lithological combination seal model, principal stress seal model and shale smear zone seal model, a fault seal model is established and fault sealing properties are quantitatively analyzed and evaluated in the Central uplift of the Dongying depression. The optimal normal stress of the sealing fault in the study area is about 40 to 50 MPa and the shale smear factors for the sealing fault is commonly <2.6. To judge whether a particular fault has sealing properties requires an integrated analysis, and one must not make single-factor analysis simply.
ANALYSIS OF THE MESOZOIC ACCUMULATION-FORMING DYNAMIC SYSTEM IN THE SOUTHERN ORDOS BASIN
ZHANG Ke-yin
2005, 11(1): 25-32.
Abstract (178) PDF (332KB)(7)
Abstract:
The main dynamic force driving the migration of Mesozoic hydrocarbons in the southern Ordos basin was mainly hydrostatic pressure in the upper part and differential compaction in the lower part. According to the dynamic characteristics, development of the hydrocarbon source and sealing conditions, four accumulation-forming dynamic systems may be distinguished:(1) the allogenic superpressure accumulation-forming dynamic system, (2) the autogenic superpressure accumulation-forming dynamic system, (3) the autogenic normal pressure accumulation-forming dynamic system, and (4) the allogenic normal pressure accumulation-forming dynamic system. Efforts should be intensified to carry out hydrocarbon exploration in the autogenic superpressure accumulation-forming dynamic system and autogenic normal pressure accumulation-forming dynamic system in the Zhenyuan-Jingchuan area, while in the Yijuan-Xunyi area the main hydrocarbon exploration targets are the allogenic superpressure accumulation-forming dynamic system and autogenic superpressure accumulation-forming dynamic system.
MECHANISM OF NATURAL FRACTURE FORMATION IN THE UPPER PALEOZOIC TIGHT SAND GAS RESERVOIRS IN THE TABAMIAO AREA, NORTH ORDOS BASIN
XING Zhen-hui, CHENG Lin-song, ZHOU Xin-gui, KANG Yi-li, ZHANG Lin-yan
2005, 11(1): 33-42.
Abstract (153) PDF (924KB)(8)
Abstract:
It is very hard to develop effectively the Upper Paleozoic low-pressure, low-porosity, low-permeability tight sand gas reservoir in the Tabamiao area, northern Ordos basin. The existence of natural fractures in tight gas sand can change the situation dramatically by improving greatly the permeability of the tight sand reservoir. The study of the development and distribution of natural fractures may help to determine the design of hydraulic stimulation and horizontal drilling program in tight gas development. The Tabamiao block is located on a slope in the north of the Ordos basin, and the strata occur as a gentle monoclinal structure with a stratigraphic dip angle of only 1° and it is generally thought that they have no conditions for natural fracture growth. However, many vertical fractures and high-angle fractures have been found through core observations, thin-section analysis and tests of physical properties, as well as well testing and logging. Studies of the shape, attitude, density and distribution of natural fractures indicate that natural fractures result from combined effects of the tectonic stress, differential compaction and very high fluid pressure, whereas faulting is the leading factor responsible for the development of the natural fractures in the area.
ANALYSIS OF THE FEATURES OF SEQUENCE STRATIGRAPHY AND SPATIAL DISTRIBUTION OF SANDSTONEs IN THE BAODAO AREA, QIONGDONGNAN BASIN
WU Li, SHI Wei
2005, 11(1): 43-52.
Abstract (180) PDF (975KB)(8)
Abstract:
Based on the principle of sequence stratigraphy, according to the analysis of seismic and well-log sequence stratigraphy, fourteen seismic depositional sequences are identified in the Tertiary of the Baodao area, Qiongdongnan basin, and the characteristics of various sequences are analyzed. In addition, the paper summarizes sandstone types in different systems tracts and analyzes in detail the spatial distribution of sandstones in different systems tracts. The study shows that the advantageous sandstones in the area have the following distribution characteristics:in the environment of growth faults, sandstones are mainly distributed in the downthrown block of a boundary fault; in a lowstand systems tract, sandstones are mainly distributed in lowstand wedges, slope fans, basin-floor fans, fan deltas, deltas and submarine canyons; in a transgressive systems tract, sandstones are mainly distributed in sandbars and sand-beaches; and in a highstand systems tract, sandstones are mainly distributed in deltas, fan deltas and submarine fans.
APPLICATION OF LOGGING INFORMATION IN THE ANALYSIS OF THE GROUND STRESS IN THE FORELAND COMPRESSIVE AREA
ZHAO Jun, PU Wan-li, WANG Gui-wen, LI Jun
2005, 11(1): 53-59.
Abstract (121) PDF (247KB)(11)
Abstract:
Compressive tectonic stress is the main stress in foreland basins in western China,where surface and subsurface structures are very complicated.Petroleum exploration and development call for not only the intensive study and prediction of ground stresses but also simple,economical and practical approximate methods.Through a comparative study of the distribution characteristics of the geophysical logging information in the structurally stable field and those in the structural compressive field,a statistical model for determining the maximum principal in-situ stress based on the logging information is proposed.This method is applied in the calculation of the stress in the Kuqa piedmont compressive area of the Tarim basin.The calculated result coincides with the result of the acoustic experiment.On that basis,the relationship between the ground stress distribution and the distribution of petroleum accumulations in piedmont compressive areas is studied.
FAULT CONTROLS ON OIL AND GAS IN THE MOSUOWAN AREA,JUNGGAR BASIN
WU Kong-you, ZHA Ming, WANG Xu-long, GUO Zhi-qiang
2005, 11(1): 60-66.
Abstract (136) PDF (305KB)(6)
Abstract:
The strata overlying the Triassic in the Mosuowan on the whole occur as a monocline and the traps are mostly related to faults,which may fall into the deep and shallow fault systems.Deep faults are reversed ones developed in the Carboniferous to Permian,while shallow faults are tensional and tenso-shear ones developed in the Jurassic.In the Late Jurassic,shallow faults were initiated and extended upward to the surface,thus causing dissipation of hydrocarbon.From the Cretaceous to Tertiary,fault sealing built up with thickening of the overlying strata.According to an analysis of the lithological combination and mudstone smear factor,the fault sealing properties of the Mobei uplift is better than those of the Mosuowan uplift,and the smear effect of mudstone in the first sandstone set (J1s21) of the Second Member of the Lower Jurassic Sangonghe Formation is better than that of the second sandstone set (J1s22) of the Second Member of the Lower Jurassic Sangonghe Formation.The hydrocarbon is diverted toward the reservoirs on two sides of the fault when it moves vertically along the fault,and the coefficient of diversion is related to the obliquity,thickness and permeability of the reservoirs.The hydrocarbon will preferentially enters the thicker and more permeable J1s22 reservoir;however,the thin and less permeable J1s22 reservoir prefers to entrap the late-stage highly mature hydrocarbon.
FORMATION CONDITIONS AND DISTRIBUTION CHARACTE-RISTICS OF LITHOLOGICAL RESERVOIRS IN THE QIANJIANG SUBBASIN
HU Hui
2005, 11(1): 67-73.
Abstract (244) PDF (281KB)(9)
Abstract:
The unidirectional,multi-source,saline-lake sedimentary system and structural background of the Qianjiang subbasin are the necessary geological conditions for the formation of a number of genetic types of lithologic reservoir in the Qianjiang saline lake.The lithologic reservoirs may be divided into 15 subtypes of 4 types.The organic combination of sandstone pinchout line and structure is the major factor responsible for the formation of the lithologic reservoirs.Vertically,lithologic reservoirs mostly occur in the Third and Fourth members of the Qianjiang Formation,and in plan view,they are mainly developed on the structural slopes facing the material source and in areas where the combinations of faults and sandstone edge pinchout are concentrated.
GENETIC MECHANISM OF NEARLY N-S-TRENDING STRUCTURE IN THE QAIDAM BASIN AND THEIR SIGNIFICANCE FOR FORMATION OF HYDROCARBON ACCUMULATIONS
CAO Chen-jie, WANG Xiao-feng
2005, 11(1): 74-80.
Abstract (179) PDF (308KB)(10)
Abstract:
Nearly N-S-trending structures are found in all basins of west-central China. They are not large in scale but have a marked controlling effect on the formation of hydrocarbon accumulations. On the basis of the research results of relevant subjects, combined with a wealth of drilling, geophysical, experimental and analytical data, and through studies of structural features, sedimentary response to tectonic movement and response to the subsurface paleotemperature field and magnetic fabric analysis, the paper systematically elucidates the features of the Cenozoic tectonic stress field in the Qaidam basin and discusses the dynamic mechanism of the formation of nearly N-S-trending structures and their prominent position and role in the formation of hydrocarbon accumulations in the Qaidam basin.
RESERVOIR CHARACTERISTICS AND EVALUATION OF THE KANGCUN FORMATION IN THE DAWANQI OILFIELD,TARIM BASIN
KUANG Hong-wei, JIN Guang-chun
2005, 11(1): 81-89.
Abstract (179) PDF (299KB)(8)
Abstract:
On the basis of stratigraphic correlation, the characteristics of reservoir rocks of the Kangcun Formation, origin, types and features of sand bodies, pore types and textures of reservoir rocks and distribution characteristics of the reservoir in the Dawanqi oilfield have been intensively studies. The Kangcun Formation of the Dawan oilfield belongs to a delta sedimentary system formed when a river with a low meandering curvature enters a very shallow lake, which determines that its main reservoir sand bodies are of deltaic sand body type. The sand bodies may be subdivided into delta plain distributary channel sand bodies, delta-front subaqueous distributary channel sand bodies and river mouth bar sand bodies. The main reservoir space types are residual primary intergranular pores and next come intergranular solution pores and micropores. The distributary channel sand bodies consist predominantly of medium and coarse sandstone, pebbly sandstone and fine sandstone, which are characterized by development of large pores and throats, high porosity and permeability and good accumulation properties, and the river mouth bar sand bodies are composed chiefly of fine sandstone and siltstone with a relatively fine grain size, a relatively low porosity, a high permeability and a relatively small pore diameter. Vertically, sand bodies are better developed in the middle and lower parts of the Kangcun Formation and less developed in the upper part, where arenaceous beds and argillaceous beds alternate with each other but generally the sandstone content is not high, commonly ranging from 15 to 30%. Laterally, due to the influence of factors such as provenance, the Kangcun Formation reservoir is thick in the northeast and thin in the northwest. The general distribution pattern of the physical properties of the reservoir is that:the porosity decreases from northeast to southwest and the permeability becomes poor from southeast to northwest.
DISTRIBUTION CHARACTERISTS OF Ro AND FACTORS INFLUENCING THE ORGANIC MATURITY IN THE ZHANHUA DEPRESSION
LI Sheng-li, YU Xing-he, CHEN Jian-yang, LI Yun-xiu, WANG Yong-shi
2005, 11(1): 90-96.
Abstract (153) PDF (212KB)(8)
Abstract:
According to an analysis of the data of temperatures and Ro in the Zhanhua depression of the Shengli oilfield, the Ro=0.4% is determined to be the Ro threshold of hydrocarbon (including immature or low-maturity oil/gas) generation in the area, and the depth threshold and temperature threshold corresponding to the new Ro average~90℃ and~2250 m respectively. The related factors responsible for the relatively low Ro value are organic components, temperature, fluid pressure and burial depth. By comparison, the Bonan and Gubei sub-depressions of the Zhanhua depression have a high hydrocarbon generating potential, while the potential of hydrocarbon generation of the Fulin sub-depression is relatively low.

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