Meso-Cenozoic Tectonic Evolution Characteristics And Its Controlling Effects On Hydrocarbon Accumulation In The Southwest Depression Of Tarim Basin

The southwest depression of the Tarim basin is located in the conjunction region among the Pamir,south Tianshan tectonic zone,western Kunlun tectonic zone,Tibet Plateau and Altun fault zone.It has experienced the complex tectonic evolution with the typical tectonic location,especially in the Mesozoic-Cenozoic.And the notably petroleum geological conditions are showed including hydrocarbon source rock,reservoir,caprock,trap and migration system,however,the relationship between tectonic evolution and associated hydrocarbon accumulation was little constrained.This paper focused on the southwest depression of the Tarim basin,aim to clarify the tectonic evolution effects on the characters of hydrocarbon accumulation,which will not only improve the scientific level of the tectonic evolutionary processes in the southwest depression but also is of great significance to the subsequent oil and gas exploration in this area.We present the data of low temperature heat chronology,methods of sedimentology and equilibrium profile,together with data from seismic,drilling,and field geological section,to study on the tectonic characteristics,events and evolutionary processes of the southwest depression in Tarim basin.Based on the methods of rock pyrolysis,thin section observation,grain size analysis,image analysis of pore throat,scanning electron microscopy(SEM),energy spectrum,the cathodoluminescence,fluorescence,X-Ray diffraction and fluid inclusion test,we studied on the characteristics of main hydrocarbon source rock,reservoir,caprock,trap,migration system and hydrocarbon accumulation.According to the analyzed data from structural evolution of petroleum accumulation geological factors,the influence of typical reservoirs in the forming processes,we will discuss the Mesozoic-Cenozoic tectonic evolutionary processes and associated geological conditions development and accumulation of petroleum in the southwest depression of Tarim basin.The results indicate that there are five-stage tectonic events of Late Trassic-Early Jurassic,Late Jurassic-Early Cretaceous,Late Cretaceous-Late Paleocene,Middle OligoceneMiddle Miocene and Late Miocene to now,responding to regional tectonic settings and geological characteristics.The development of the structures such as fold,fracture,reverse thrust,faulted transition fold,double structure,triangular belt and unconformity are closely related to the evolution of tectonic events,which are mainly influenced by Late Triassic-Early Jurassic regional uplift,Middle Oligocene-Middle Miocene intense tectonic squeezing and rapid uplift of Late Miocene up to now.Carboniferous-Lower Permian is a set of widely distributed highly mature hydrocarbon source rock with medium abundance and?kerogen type,however,the good abundance hydrocarbon source rock of the Middle and Lower Jurassic is limitly distributed in the piedmont region of the west Kunlun tectonic belt,mainly ? kerogen type,at the evolutionary stage of mature to highly mature.Kezilesu group is regarded as a alluvial fan facies lithic sandstone reservoir by rapid deposition of proximal source,and its maturity of both structure and component are very low.It is at the A-stage of mesodiagenesis and mainly composed of primary pores and secondary dissolution pores.The Kezilesu sandstone and the overlying Aertashi gypsum rock are composed of a high quality combination of reservoir-caprock in the piedmont area,which was developed two-stage hydrocarbon accumulation of Late Jurassic to Pliocene.The overall uplift from Late-Trassic to Early-Jurassic decreased the thermal evolution level of source rocks,so that it provided robust foundation for the following hydrocarbon accumulation.The strong uplift during Middle Oligocene-Middle Miocene resulted in the interaction of rapidly burial hydrocarbon generation,high angle thrust fracture migration and trap entrapment,which played a key role in the petroleum accumulation in this region.And the rapidly uplift after Late Miocene strengthened the accumulation.As a result,the hydrocarbon was mainly accumulated during late stage in this region.