Evaluation Of Hydrocarbon Generation Potential Of Taiyuan Formation Limestone In Central And Eastern Ordos Basin

The Ordos Basin is rich in oil and has a number of oil-bearing stratum gas resources distributed in the Paleozoic and Mesozoic Regions,and has become the largest oil and gas production basin and the largest natural gas production area in China.With the deepening of exploration,high-yield gas reservoirs have been found in the Xiedao limestone and Maoergou limestone of the Lower Permian Taiyuan Formation in the study area.In recent years,researchers have also carried out detailed research on their reservoir characteristics and accumulation models,and achieved a lot of results and progress.In this process,it is found that the limestone gas reservoir of Taiyuan Formation has the characteristics of mixed source of coal-type gas and oil-type gas.It is urgent to evaluate the hydrocarbon generation capacity of limestone outside the mud shale and coal-measure source rocks of Taiyuan Formation,and analyze its contribution to the Upper Paleozoic gas reservoir,so as to provide theoretical support for the next exploration process of the oilfield.In this study,the limestone of Taiyuan Formation in the central and eastern part of Ordos Basin was taken as the research object.Based on core observation,logging data,geochemical experimental data and previous research results,the sedimentary environment and organic geochemical characteristics of the limestone of Taiyuan Formation in the study area were systematically analyzed.On this basis,the thermal simulation experiment of hydrocarbon generation(Gold tube closed system)was carried out by selecting samples,and the hydrocarbon generation chart of Taiyuan Formation limestone in the study area was established.The results show that:(1)The Taiyuan period in the study area is mainly a mixed sedimentary tidal flat environment,which has experienced multiple transgressions and regressions to form four sets of transgressive limestone and coal measures deposits.The limestone is mainly developed in the subtidal zone,which can be divided into three microfacies:bioclastic beach,bioherm and ash flat.The western part of the study area is mainly bioclastic beach deposition,and the eastern part is bioherm deposition.(2)The organic matter type of limestone also has the characteristics of sea-land mixed source,but it is mainly type I.In the case of good organic matter type,although the organic matter abundance of Taiyuan limestone is generally lower and the maturity is higher than that of shale,it still has certain hydrocarbon generation potential in the previous criteria for the lower limit of TOC of high maturity carbonate source rocks.The limestone lithofacies are variable vertically,the plane distribution is obviously different from east to west,and the organic matter abundance is significantly different.In this evaluation,the effective source rock still has a large thickness.(3)Based on the analysis of the thermal simulation experiment of hydrocarbon generation in the gold tube sealing system,combined with the understanding of sedimentology,the gas generation amount of Taiyuan Formation limestone in the study area is calculated to be about 7200×10~8m~3,which has a certain contribution to the gas accumulation of Taiyuan Formation.This study is the first time to study the organic geochemical characteristics and hydrocarbon generation potential of Taiyuan Formation limestone in the central and eastern Ordos Basin,and establish a limestone hydrocarbon generation chart and gas generation calculation,in order to provide help for subsequent researchers and oil field exploration.