Anatomy Of Oil And Gas Reservoirs In Dibei Gas Field,Northern Kuqa Structural Belt

Kuqa Depression is the main battlefield of natural gas exploration in Tarim Basin.In recent years,the exploration of tight sandstone gas in the northern tectonic belt has gradually increased,and many scholars have studied it.However,the study of complex low permeability-tight hydrocarbon accumulation period and process in Dibei Gas Reservoir is relatively low,the source of oil and gas is controversial,and the understanding of the main controlling factors is still unclear.In this paper,the source rocks and crude oil samples in the study area are analyzed by geochemical experiments,the carbon isotope characteristics of natural gas and light hydrocarbon parameters are analyzed,and the microscopic inclusion observation is combined with other methods.On the basis of static analysis of hydrocarbon reservoir-forming conditions in dynamic dissection of reservoir-forming process and combined with the latest exploration results,the reservoir-forming model is established,and the main controlling factors of Dibei gas field are defined.The following understandings are obtained:(1)According to the carbon isotope characteristics and light hydrocarbon parameters of natural gas,the mixed source characteristics of oil and gas are clarified.Combining with the biomarker characteristics of crude oil,it is determined that oil and gas mainly come from lacustrine mudstone at the top of Yangxia Formation and coal measures hydrocarbon source rocks at the bottom.Two sets of source rocks developed in Yangxia Formation have different petroleum geochemical properties,mainly due to differences in sedimentary environment and parent material sources.(2)Through the observation of inclusions under the microscope,the characteristics of early and late accumulation of oil and gas in Dibei gas reservoir are defined.By measuring the homogenization temperature of brine inclusions and combining with the burial history curve of formation temperature in this area,the hydrocarbon accumulation period is defined,Kangcun period is the reservoir formation time,and the peak of exhaust gas occurs in Kuqa period.(3)Combining with previous research results,it is determined that Dibei gas reservoir is a tight deep basin gas reservoir of "first compact and then reservoir-forming type",and the main controlling factors of hydrocarbon accumulation are analyzed.In the future exploration process,we should pay attention to the development area of fractures.The main fracture is structural fracture,which is not filled.It can improve gas saturation and gas filling efficiency.It is a "dessert" for exploration of tight sandstone gas reservoirs in Dibei.