Study On The Controlling Factors Of Hydrocarbon Accumulation In Maokou Formation Of Permian In East Sichuan

Maokou Formation of Permian in Sichuan Basin has always been an important stratigraphic system for carbonate oil and gas exploration.The exploration effect of Maokou Formation of Permian in East Sichuan is remarkable,showing a good exploration prospect of karst fracture cave reservoir in Maokou Formation of East Sichuan.Based on the analysis of the controlling factors of oil and gas accumulation of Maokou Formation in East Sichuan,this paper hopes to provide reference for the oil and gas exploration of the Permian Maokou Formation.Based on the analysis of the composition and isotopic characteristics of natural gas in gas reservoir of Maokou Formation of Permian in East Sichuan,the main source rock series of natural gas in gas reservoir of Maokou Formation is determined.Based on the core and thin section observation,combined with cathodoluminescence,trace elements in situ micro area and isotopes in situ micro area,the controlling factors of reservoir development in Maokou Formation are analyzed.According to the diagenetic evolution of Maokou Formation,the petrographic characteristics,homogenization temperature and composition of fluid inclusions captured by minerals in different periods are analyzed.Combined with regional burial history,the oil and gas accumulation stages and time of Maokou Formation are determined.Based on the drilling data and the interpretation results of two-dimensional seismic grid,the structural form of top surface of Maokou Formation in different periods in the study area is depicted,the formation and evolution process of typical gas reservoirs in Maokou Formation is restored,and the reservoir forming model is established.Based on the study of the hydrocarbon generating potential of gas source rock,the controlling factors of reservoir development,the formation and evolution of oil and gas reservoir,the controlling factors of Maokou Formation reservoir in East Sichuan are analyzed.The understanding of this paper is as follows:(1)The natural gas in Maokou Formation gas reservoir of Permian in East Sichuan mainly comes from Silurian and Permian source rocks.The two sets of source rocks in the study area are widely distributed and thick.The Silurian source rocks are mainly composed of type I organic matter,and the Permian source rocks are mainly composed of type II organic matter.The residual organic carbon content is generally high and the hydrocarbon generation potential is good.(2)The main diagenesis of the Permian Maokou Formation in East Sichuan includes cementation and filling,dissolution,fracture and dolomitization.The supergene karstification and dolomitization are the most important diagenesis affecting the reservoir development of Maokou Formation in the study area.(3)There are three stages of oil and gas accumulation in Maokou Formation of Permian in East Sichuan,the fourth stage is gas reservoir adjustment and transformation;the first stage is paleo oil reservoir formed in Late Triassic,the second stage is paleo oil and gas reservoir formed in middle-Late Jurassic,the third stage is paleo gas reservoir formed in Early Cretaceous,and the fourth stage is paleo gas reservoir adjustment and finalization since Late Cretaceous.(4)The reservoir formation and evolution of the Maokou Formation of Permian in east Sichuan were restored;during the Indosinian movement of the Late Triassic,paleo oil reservoirs developed at the structural highs such as Tanmuchang on the paleo uplift and Longhuichang outside the paleo uplift;in the early Jurassic,the scope and extent of structural traps such as Tanmuchang and Longhuichang were further expanded,and paleo oil and gas reservoirs continued to form;during the Yanshan movement of the early Cretaceous,paleo oil and gas reservoirs were transformed into paleo gas reservoirs,The structural form of Tanmuchang on the paleouplift continues to maintain,Longhuichang and other structures outside the paleouplift are greatly uplifted;since the late Cretaceous,Kaijiang paleouplift has basically disintegrated,and the paleogas reservoir is controlled by the paleouplift and Himalayan tectonic movement,which is adjusted and finalized as the distribution pattern of the present gas reservoir.(5)The oil and gas accumulation model of Maokou Formation of Permian system in East Sichuan is established;the structure represented by Longhuichang was in the relatively low part of Kaijiang paleouplift in the early stage,but its trap formed early,adjusted to the high part of structure in the late stage,with the characteristics of "early accumulation and late accumulation";The structure represented by Tanmuchang was in the range of Kaijiang paleouplift,which is relatively stable from the formation of paleo reservoir in Late Triassic to the formation of paleo gas reservoir in Early Cretaceous.The adjustment range of Tanmuchang structure is small during Himalayan movement,which is an "in situ" type of oil and gas accumulation.(6)The controlling factors of oil and gas accumulation in Maokou Formation of Permian are:(1)the development of high-quality source rock is the basis of oil and gas accumulation;(2)the development of high-quality reservoir is the key of oil and gas accumulation;(3)the matching of structural evolution and accumulation period is the core of oil and gas accumulation;(4)good preservation conditions are the guarantee of oil and gas accumulation.Among them,the development of high-quality reservoirs and good preservation conditions are the main controlling factors of hydrocarbon accumulation in the study area.