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2002 Vol. 13, No. 4

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Discussion on Petroleum Migration in Bamianhe Oilfield of Dongying Depression, East China
Xiongqi Pang, Sumei Li, Zhijun Jin, Xiaochang Ma
2002, 13(4): 297-305.

Petroleum migration process of Bamianhe oilfield of Dongying depression, East China is evaluatedon the basis of our detailed work on geochemistry of the crude oil and the source. Molecular tracers, especially nitrogen compounds, are employed in assessing style of oil migration and accumulation. Additionally, absolute quantitative results of heteroaromatics including dibenzofuran, dibenzothiophene and fluorene with similar basic frames to pyrrolic nitrogenic compounds are also used to evaluate the quantity of petroleum migration. According to apparent migration effects of the pyrrolic nitrogen compounds, it is indicated that most of Bamianhe oil was derived from potential source kitchen-Niu-zhuang sag, migrated and accumulated at Bamianhe fault belt through selective paths according to a main filling point displayed. Generally, upward migration trend from the main point along the south slope is noted. There are observable migration effects from Guangli subsag to the north Bamianhe and Yangjiaogou oilfields showing Guangli subsag was a secondary kitchen accounting for the oils in the north portion. Significant vertical migration effects shown in several cross sections demonstrate that faults well developed in the area play an important role in oil migration and accumulation. Unformality, sandstone reservoirs distributed locally also suggest important fairways in connecting sources with traps. The tectonic and a combination of tectonic and lithological mechanism are identified as the critical mechanisms in entrapping hydrocarbons. Migration trend suggested by nitrogenic compounds agrees well with analysis of lateral compositional variety and thermal maturity gradient. This study also confirms well with our previous studies. It is the location of source rocks, tectonic and stratigraphic characteristics that have a comprehensive control on the model of hydrocarbon migration and accumulation in Bamianhe oilfield. Results also show that the oils are mostly derived from the deep parts of the Niuzhuang and Guangli sags within normal oil window.

Division of Gas Accumulation System and Laws Controlling Distribution of Natural Gas in Typical Petroliferous Basins of China
Zhenxue Jiang, Xiongqi Pang, Zhijun Jin, Dongxia Chen
2002, 13(4): 306-312.

Considering the existing problems of the petroleum system, this paper brings forward the concept of natural gas accumulation system and presents the dividing principles. Then detailed statistics on the accumulation factors of the 32 typical natural gas accumulation systems in China and studies on the laws controlling distribution of gas are collected. The research shows that the petroleum accumulation system is the basic unit controlling petroleum generation, migration and accumulation. Generating intensity, generating amount, accumulating efficiency and migration distance plays an important role in the distribution of natural gas. Through analysis on results of resources evaluation, discovered reserves and residual reserves, potential areas in middle-scaled petroliferous basins in China are forecasted in this paper. Ordos, Sichuan, Tarim and Qaidam basins are found out to be the main basins developing and enriching gas accumulation systems.

Analysis Method for Predicting Strain in Interior Beds and Sub-Resolution Faults from Area Balance Theory in Extensional Basins
Jiafu Qi, Jr R H Groshong, Qiao Yang, Shuping Chen
2002, 13(4): 313-320.

Extensional basins include mainly grabens and half grabens displaced along a lower detachment. Based on area balance theory, there is a linear relationship between a height of regional and the lower detachment h on the outside of the basin and "lost area S" from the regional in the basin. The pre-growth beds above lower detachment are of the same extensional displacement so that an "S-h diagram" can be used to determine the depth to lower detachment and to calculate the total extensional displacement of the beds above the lower detachment. The extensional displacement is dominated by the heave of various scale normal faults. The displacement of obvious faults can be immediately figured out from the measured bed-length. The requisite extension calculated by area balance is the layer-parallel strain, which could be accommodated by displacement on sub-resolution faults. Accordingly, the layer-parallel strain can help us predict the magnitude and distribution of sub-resolution faults on the basis of analysis of the structural style and rheological behavior.

Middle Ordovician Bioturbation Structures from Southeastern Margin of Ordos Basin and Their Environmentary Interpretation
Anwei Fei, Zhongtao Zhang
2002, 13(4): 321-329.

Trace fossils were discovered in the Middle Ordovician Badou Member of Fengfeng Formation and the Member 1 of Jinsushan Formation in Mt. Jinsu of the Fuping region which lies at the southeastern margin of the Ordos basin. The rocks of the fore-mentioned parts contain a considerable amount of bioturbation structures, in which ichnogenus and ichnospecies can not be identified, and abundant stromatolites.The distributions and characteristics of the bioturbation structures are analyzed and summarized in this paper. The paleoenvironments of related formations and members were interpreted in the method of semiquantitative analysis of bioturbation structures with researches on stromatolites and sedimentology. It is suggested that Fuping zone, located in the southeastern margin of the Ordos basin, was a carbonate platform where stromatolite-developing tidal flat and low-energy subtidal open platform environments dominated. Also that this zone experienced three paleogeographic evolutions from tidal flat to low-energy subtidal open platform environments, that is, three larger-scale eustatisms occurred during the sedimentary period of Middle Ordovician Badou Member of Fengfeng Formation to the Member 1 of Jinsushan Formation.

Distribution and Significance of Methyl Steranes in Bohai Bay Basin, East China
Li Sumei
2002, 13(4): 330-337.

samples of shales and mudstones developed in reducing hypersaline and freshwater setting and 20 oil samples of Bamianhe oilfield, Bohai Bay basin were collected for a detailed study of petroleum system. Composition and distribution, especially significance of steroids, are discussed as a part of those. Abundant steroidal biomarkers, including C27-29 regular steranes, C28-30 4-methyl steranes, dinosteranes and aromatic steranes, were detected. Results show that the composition and distribution of the steroids in samples studied are functions of thermal maturity, organic source, paleoenvironment and lithology of potential source rocks. Alga-rich Es4 shales (brackish water) developed in the south slope of depocenter (Niuzhuang sag) were found particularly rich in steroidal biomarkers including C30 4-methyl steranes and dinosteranes. Es3 mudstones (fresh water) were found devoid of dinosteranes. Distribution patterns of regular steranes are completely different from methyl steranes indicating different origins of the specific compounds of the fraction. Diagnostic distribution of steranes in rock extracts of diverse intervals makes the compounds to be essential indictors of source-rock tracing. Methyl steranes prove to be much more useful in oil-source rock correlation than regular steranes. Results also show that alga-rich Es4 shales located in the south slope are not likely the primary source rock responsible for the oils discovered based on the composition and distribution of steroids.

A Study on Identification of Conglomerate Reservoir Parameters and Oil/Water Beds in Ke82 Well Areas of Junggar Basin
Guiwen Wang, Qing Zhang, Mingrui Li
2002, 13(4): 338-344.

This paper is mainly about the calculation of reservoir parameters and theinterpretation method for identifying oil/water beds in Ke82 well areas of Junggar basin. It isdifficult to determine the reservoir parameters with common logging methods such as core calibrationlog because of the diversity of minerals and rocks and the complexity of pore structures in theconglomerate reservoir of Junggar basin. Optimization logging exploration is a good method todetermine the porosity by establishing the multi-mineral model with logging curves based on theintegration of geological, core and well testing data. Permeability is identified by BP algorithm ofneural network. Hydrocarbon saturation is determined by correlating Archie's and Simandouxformulas. Comparing the exploratory result and core data, we can see that these methods areeffective for conglomerate logging exploration. We processed and explained six wells in the Ke82well areas. And actual interpretation has had very good results, 85 % of which conform to welltesting data. Therefore, this technique will be effective for identifying conglomerate parameters.