Hydrocarbon Generation And Expulsion Characteristics Of Paleogene Source Rocks And Their Controlling Effects On Hydrocarbon Accumulations In The Southwest Of Huizhou Sag

Huizhou Sag is the largest and most hydrocarbon-rich sag in Pearl River Mouth Basin.In recent years,with the expansion of exploration field,the Paleogene in Huizhou Sag shows good exploration prospects.Source rocks are the basis for generating oil and gas,and their hydrocarbon generation and expulsion characteristics directly affect the distribution characteristics of oil and gas resources and control the distribution of oil and gas reservoir.The Paleogene is deeply buried in Huizhou Sag,with few drilled wells,and the study of source rocks is not systematic and in-depth enough.The hydrocarbon generation and expulsion characteristics of source rocks and their controlling effects on hydrocarbon accumulations are not clear.Based on the analysis of the geological and geochemical characteristics of Paleogene source rocks,the improved hydrocarbon generation potential method was used to establish the hydrocarbon generation and expulsion model in the study.The hydrocarbon generation and expulsion threshold was determined,the hydrocarbon generation and expulsion characteristics was analyzed,and the oil and gas resource potential were evaluated.The quantitative model of source-controlled oil and gas reservoir distribution was established by the theory of source-controlled oil and gas distribution.The role of Paleogene source rock in controlling oil and gas distribution was analyzed.Finally,favorable exploration areas were predicted in combination with the distribution characteristics of sedimentary facies.The results show that two sets of source rocks in the Paleogene,Wenchang Formation and Enping Formation,are developed in the southwest of Huizhou Sag.Wenchang Formation is the main source rock,and its quality and hydrocarbon generation potential are better than that of Enping Formation.The hydrocarbon generation and expulsion threshold of Wenchang Formation are Ro=0.43%and Ro=0.56%,respectively.The hydrocarbon generation and expulsion threshold of Enping Formation are Ro=0.54%and Ro=0.62%,respectively.The Paleogene source rocks are in the stage of large-area hydrocarbon generation and expulsion,and the hydrocarbon generation and expulsion centers are consistent on the plane.The hydrocarbon generation and expulsion intensity of Lower Wenchang Formation in each layer is the largest,with the maximum hydrocarbon generation and expulsion intensity reaching 39388.43×10~4 t/km~2 and38928.14×10~4 t/km~2,respectively.The hydrocarbon generation and expulsion intensity of Huizhou 26 sub-sag is the largest among all sub-sags.The cumulative hydrocarbon generation and expulsion of Paleogene source rocks is 685.67×10~8 t and 647.79×10~8 t in the southwest of Huizhou Sag.The total resource of Paleogene is 82.40×10~8 t,and the resource of Lower Wenchang Formation is the largest,50.68×10~8 t.The Paleogene petroleum system is mainly divided into three stages in Huizhou Sag,are 20～13 Ma,13～9 Ma,and 9～0 Ma,respectively.The boundary of source rocks controlling the distribution of oil and gas reservoirs is the hydrocarbon expulsion radius 3 times from the center of hydrocarbon source stoves.The probability of source-controlled oil and gas is distributed in a circular belt along the hydrocarbon expulsion center of source rocks,and the reservoir-forming probability at the hydrocarbon expulsion boundary is the largest.It is predicted that the most favorable exploration areas are Huizhou 26 sub-sag and Xijiang24 sub-sag,and the most favorable formation is the Lower Wenchang Formation,which can be used as the future exploration area.The research clarified the hydrocarbon generation and expulsion characteristics of Paleogene source rocks and their controlling on oil and gas reservoirs in the southwest of Huizhou Sag,and assessed the oil and gas resources potential.This study is helpful to guide the more accurate search for oil and gas reservoirs within the hydrocarbon expulsion boundary of source rocks and reservoir forming system,and provides an important theoretical guidance for oil and gas exploration and development of Paleogene in Huizhou Sag.