Assessment On High Quality Source Rocks In The Weixinan Depresion

After many years of exploration in the southwestern depression of the Beibu Bay Basin,nearly 500 million tons of oil and gas reserves have been discovered and there is a good prospect for exploration.However,there are still many problems in the evaluation of source rock in the study area.For example,the geochemical characteristics of high-quality source rocks are not well studied,the distribution and main control factors of source rocks are not clear,and the evaluation of oil and gas generation potential is not precise enough.Therefore,in this paper,we used the geological and geophysical evaluation methods of high-quality source rocks to define the characteristics and distribution of high-quality source rocks in the Weixinan Sag,identify the main controlling factors for the development of high-quality source rocks,and combined basin simulation techniques to determine the hydrocarbon generation potential of high-quality source rocks in this area,and then divide the favorable exploration zone.The oil source comparison results show that the crude oil in the Weixinan Sag mainly comes from the source rocks of the Liushagang Formation,among these,Liu-1,Liu-2 and Liu-3 are the main source rocks in this area.By comparing the sedimentary and geochemical characteristics of high-quality source rocks in different sub-sags and different intervals in the Weixinan Sag,the characteristics of high-quality source rocks in different sub-sags and different intervals were identified,and the organic carbon content of high-quality source rocks in this area was determined.The lower limit is 2%,and the lower limit of the organic shale content of oil shale is 5%.Log evaluation models and seismic evaluation models were established to qualitatively and quantitatively predict the distribution of high-quality source rock in the study area.The development of high-quality source rocks in this area is controlled by tectonic activities and sedimentary filling macroscopically.Tectonic activities provide space for the formation of high-quality source rocks,and sedimentary filling affects lake evolution and climate change;The formation of high-quality source rocks is controlled by the supply and preservation conditions of organic matter.The development of algae and terrestrial sediments provide the supply of organic matter;temperature stratification and salinity stratification oflake water provide the preservation of organic matter.Conditions,comprehensive analysis,and determination of the main controlling factors for the development of high-quality source rocks in the Weixinan Sag.The evaluation of the hydrocarbon generation potential of high-quality source rocks in the Weixinan Sag is mainly based on basin modeling.Combined with the latest research results on tectonic and sedimentary materials,the latest 3D seismic data from the Weixinan Sag are used to evaluate the latest high-quality hydrocarbon source rock.Using basin simulation techniques,the hydrocarbon generation potential and direction of oil and gas migration of high-quality source rocks in the Weixinan Sag are identified.Based on the basin simulation results and analysis of the main controlling factors of high-quality source rocks,the integrated sand bodies,structural traps,and the range of high-quality source rocks,comprehensive analysis was conducted to determine the Weizhou11-4N structure,the middle section of the No.1 fault and the eastern section.the structural trap area in the middle fault section of No.2 are favorable exploration zones,and Wei-3,Liu-1 and Liu-3 are favorable exploration targets,thus providing guidance for the next exploration in this area.