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Comparison in Petroleum Geology between Kuqa Depression and Southwest Depression in Tarim Basin and Its Exploration Significance
详细信息   
摘要
Petroleum exploration in the southwest Tarim Basin has a history more than sixty years.Up to now,five oil and gas fields and two oil and gas reservoirs have been discovered,namely Kekeya,Bashituopu,Yasongdi,Hetianhe,Akemomu,and the Shan-1 well and Kedong-1 well.Petroleum geologists and explorationists have cherished high hopes for these favorable and prospecting areas and all along pursued goals how to understand their petroleum geological conditions in detail,to accelerate exploration activities,and to get much more discoveries.In addition,a great breakthrough has been made in gas exploration of Kuqa area in Tarim Basin since 2000.Therefore,the petroleum geologic comparison between these two depressions is one of the important methods to analyze and uncover key petroleum geologic conditions of Southwest depression.Based on available exploration data and the current knowledge of these two depressions,we compared the very similarities and differences between them from the point of view of comparative tectonics and petroleum geology.Both of them share the following common points:(1) boundaries between the basin and mountains are characteristic of overthrusting or strike-slipping-overthrusting;(2) they have the intra-continental foreland basin structures at present;(3) they are formed by the transformation and superimposition of different proto-type basins;(4) basin structures are characterized by segmentation,zonation and stratification;and(5) fault zones play a major role in controlling hydrocarbon accumulation.However,differences between these two depressions are also much more remarkable in twelve aspects,such as geo-tectonic settings,deep geological structures,basement properties,tectonic evolution,geological framework,structural deformation,source rocks and their thermal evolution,reservoir-seal rock associations,petroleum systems,oil and gas accumulation mechanisms and preservation patterns,and oil and gas distributions.Of which the overwhelming important factors that control the oil and gas reservoir-formation are the geo-tectonic background and geological structures.The former shows that Kuqa depression is tightly related to the Paleo-Asian Ocean tectonic system,while Southwest depression to the Tethyan Ocean tectonic system.The latter indicates that Kuqa depression is formed predominantly by the superimposition of Cenozoic strata upon Mesozoic strata,while Southwest depression chiefly by the superimposition of Cenozoic strata upon Paleozoic strata.The above-mentioned comparison shows clearly that exploration in Southwest depression must be supported by a new theory of petroleum geology and exploration philosophy.This new theory needs to definitely disclose the exact locations,status,types,and possible mechanisms of the oil and gas sealed and preserved under late-period extensive structural movements,which have been sourced from old and lower-seated source rocks.It is urgent for this new exploration philosophy to establish new concepts of 3D geological structures,ideas of unitary and dynamic exploration,and also the stereoscopic thinking,which strengthen not only complex structural traps in foreland belts,but also subtle traps in slope zones,i.e.Ordovician buried-hills and Devonian-Carboniferous stratigraphic-lithologic traps,as well as dolomitic traps adjacent to Cambrian source rocks.

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