Evaluation Of Paleogene Effective Source Rocks In The Liaodong Bay Depression

The Liaodong Bay Depression is an important oil and gas production area and exploration area.Through 40 years of exploration,more than 20 oil and gas fields have been discovered one after another,which has made great contributions to China's economic construction.However,with the deepening of exploration,especially the development of the 3D seismic contiguous work in the whole region,we need to have a comprehensive understanding of source rocks,oil and gas-based geology and so on,among these,how to understand the deep layer(the lower part of the Sha-3 section to Kongdian Formation),the accumulation of source rocks in the marginal sags,the main controlling factors and depositional models for the development of source rocks,and the quantitative evaluation of hydrocarbon generation and expulsion from effective source rocks have not only affected the prediction accuracy of oil and gas resources,but also constrained the selection of exploration targets.Therefore,in this paper,we used the geochemical,logging,and seismic data,in combination with the tectonic and sedimentary backgrounds of the Liaodong Bay Depression,and conducted an effective evaluation of the source rocks.Firstly,we carried out the core observations and basic geochemical characteristics of hydrocarbon source rocks in different layers of depressions,analyzed for oil source analysis parameters such as biomarker compounds,and identified the oil and gas accumulation zones and effective source rock formations for different hydrocarbon accumulation zones.Then,we proposed a set of evaluation methods of source rock for well logging based on comprehensive organic geochemistry and well logging information to evaluate the source rocks of 206 exploration wells in the study area.In addition,a combined log-seismic information extraction and inversion study was carried out for less wells or no well regions in deep formations,the TOC and thickness prediction methods for source rocks were proposed to predict source rocks that could not be evaluated in the past.Finally,basing on the basin structure,sedimentary filling,and organic matter conservation conditions,we used the parameters such as sedimentation rate/structure settlement rate,fault extension amounts,submarine fan area/secondary sub-sag area,and the degree of stratification are the main controlling factors for the development of effective source rocks,and two separate stratified water models for hydrocarbon source rocks were established:deep-water temperature stratification source rock deposition model in separate lake basin and salinity stratified water source rock sedimentary model in salinity lake basin.By recovering the original TOC of each set of source rocks,the oil and gas generation intensity is obtained by using oil and gas production simulation experiments and source rock evaluation results;the oil and gas discharge rate is calculated by using oil and gas generation,porosity reduction and hydrocarbon saturation during the burial of source rocks,then the oil and gas discharge intensity was obtained.According to the evaluation results,we found that the oil and gas generation intensity of the main source rock is more than 200×10~4t/km~2(oil discharge intensity>125×10~4t/km~2),the adjacent area can form an oilfield with a reserve of over 5000×10~4t,when the oil generation intensity is lower than 25×10~4t/km~2(oil discharge intensity<15×10~4t/km~2),no scale oil and gas reserves were found in the adjacent area.According to the oil and gas drainage intensity,a comprehensive evaluation standard for effective source rock was established.According to the evaluation results of effective source rocks,the favorable areas/trap groups in the hydrocarbon-rich depressions are in the Liao Zhongbei sub-sag,Liao Zhongzhong sub-sag and the northern region of Liaoxibei-zhong sub-sag should be further explored,the southern region of Liaoxibei-zhong sub-sag,the Nan secondary sub-sag of Liaoxinan sub-sag should be avoided to dig the wells.Therefore,the evaluation of effective source rocks in the Liaodong Bay depression has played a very important role in guiding oil and gas exploration in the next step.