Hydrocarbon Generation Kitchens And Their Petroleum Systems In The Carboniferous-permian In The Dagang Oilfield

Carboniferous-Permian is an important hydrocarbon-generating horizon in the Dagang Oilfield.At present,oil and gas reservoirs have been found in Wumaying and Qikou sags,which indicates that the Upper Paleozoic has good hydrocarbon-generating potential and exploration prospects.However,due to multi-stage tectonic movements,there are still problems in source rock distribution,hydrocarbon generation process and hydrocarbon resource potential.On the basis of previous studies,this paper evaluates and predicts the characteristics and distribution of hydrocarbon source rocks by using downhole samples,logging and analysis test data,combining with the tectonic and sedimentary background of exploration area,summarizes and classifies four types of hydrocarbon generation process,and obtains hydrocarbon generation intensity of hydrocarbon source rocks by using hydrocarbon generation thermal simulation experiment,thus calculates hydrocarbon generation of nine evaluation units and predicts key exploration areas.Based on the study of source rocks,a Carboniferous-Permian petroleum system is divided.The source rocks in Dagang Oilfield are mainly coal,carbonaceous mudstone and dark mudstone with high abundance of organic matter.The main types of organic matter are type III and type II₂,and part of type II₁.By observing core and microscopic macerals,it is found that coal can be further divided into bright coal and dark coal,carbonaceous mudstone into inferior coal and carbonaceous mudstone,and dark mudstone into lacustrine mudstone and lagoon mudstone.According to the structural and thermal evolution characteristics of the study area,the hydrocarbon generation process of source rocks can be divided into four types:primary hydrocarbon generation,secondary early hydrocarbon generation,secondary late hydrocarbon generation and tertiary hydrocarbon generation.According to hydrocarbon generation stages of source rocks,Dagang Oilfield is divided into nine evaluation units.Based on the thermal simulation experiment of hydrocarbon generation,the horizontal distribution of oil generation intensity and gas generation intensity of Early Mesozoic,Late Mesozoic and Cenozoic source rocks is predicted.On this basis,the hydrocarbon generation of Carboniferous-Permian in different periods of each evaluation unit in Dagang exploration area is calculated.Through comprehensive evaluation,YG1 unit and QG8 unit have large hydrocarbon generation,which are favorable oil and gas accumulation areas and key exploration areas in Dagang Oilfield.Based on the study of source rock characteristics,the characteristics of YG1 well crude oil in Dagang South Area were analyzed by full-two-dimensional gas chromatography-time-of-flight mass spectrometry(GC×GC-TOFMS).It was found that the saturated hydrocarbons were characterized by pre-peak type,Pr/Ph value was 2.80,Tm>Ts,C₂₇,C₂₈,C₂₉ sterols were asymmetrically L-shaped,rich in pregnanes and rearranged sterols,and coal-derived oil characteristics were obvious.Reservoir-cap assemblage and reservoir-forming process in the southern Dagang Oilfield are studied.It is found that the reservoir-forming elements are well allocated.Therefore,an oil-gas system,namely the Carboniferous-Permian oil-gas system in YG1 Unit,is divided into the Upper Paleozoic.