Natural Gas Accumulation Conditions And Enrichment Rules Of Taiyuan Formation In The North Of Shenmu

The northern part of Shenmu gas field is the periphery of Shenmu gas field exploration in recent years.The tight sand of Upper Paleozoic has the characteristics of multi-layer gas content,showing great exploration potential.At present,the understanding of reservoir-forming geological conditions in this area is mainly concentrated in Shenmu and its southern area,while the research in the northern part of Shenmu is relatively weak.The exploration practice shows that the gas-water distribution of the Upper Paleozoic gas reservoir in the northern area,including the Taiyuan formation,is more complex,so this study is helpful to deeply understand the reservoir-forming geological conditions and the law of natural gas enrichment in the periphery of Shenmu gas field.so as to guide exploration and production.On the basis of previous studies,this study makes use of drilling geology,well logging and gas production test data,combined with organic matter source rock evaluation,core reservoir physical properties,natural gas geochemistry and formation water salinity and other test and analysis data.the development characteristics of reservoir-forming geological conditions of Taiyuan formation gas reservoir are studied systematically.The evaluation focuses on the quality evaluation of source rocks,the recovery of hydrocarbon generation potential and hydrocarbon generation history.On this basis,combined with the section anatomy of gas reservoir,the characteristics and law of gas-water distribution,the main controlling factors and enrichment rules of Taiyuan formation gas reservoir in this area are summarized,and the evolution model of natural gas reservoir formation of Taiyuan formation is established.The results show that the gas source conditions of Taiyuan formation in the study area is good,the natural gas is characterized by alkane gas and high methane content,the type of natural gas is coal type gas.The source rocks are mainly dark mudstone and coal seam,and the abundance of organic matter is high,the type of organic matter tends to type?(humus type)kerogen,and the maturity of organic matter is in the mature-high mature stage as a whole.It is calculated that the average hydrocarbon generation intensity of the source rocks of Taiyuan formation is 3.60×10⁸m³/km²,and that of the Upper Paleozoic source rocks in the north of Shenmu area is 18.11×10⁸m³/km².The reservoir lithology of Taiyuan formation is mainly lithic quartz sandstone and lithic sandstone,and the reservoir physical property is poor,which is a typical tight sandstone reservoir.Regional caprock and direct caprock are developed in the study area,and the source-reservoir-cap assemblage is self-generating and self-storage type.The types of traps developed are lithologic traps and structural-lithologic composite traps.The type of formation water is calcium chloride type(Ca Cl₂),which indicates that Taiyuan formation has good formation sealing and relatively stable hydrodynamic environment,which is beneficial to the accumulation,accumulation and preservation of natural gas.The Upper Paleozoic natural gas reservoir is divided into two stages of filling,the early filling occurred in the Early-Middle Jurassic,the filling scale was small and failed to accumulate into the reservoir,and the late filling occurred in the late Jurassic-early Cretaceous,when the organic matter entered the peak period of gas generation,at which time the trap had been formed and filled into the tight reservoir.The main controlling factors and enrichment rules of natural gas reservoirs in Taiyuan formation in the study area are as follows:the regional structure has no obvious controlling effect on the enrichment of natural gas reservoirs.The extensive hydrocarbon generation of source rock lays the material foundation for the gas reservoir,and the hydrocarbon generation intensity controls the distribution range of natural gas reservoir.Taiyuan formation gas reservoir is controlled not only by Taiyuan formation source rocks,but also by Shanxi formation and Benxi formation source rocks.The distribution and scale of sand bodies control the lateral distribution and scale of natural gas,and the physical properties of high-quality reservoirs are still favorable zones for natural gas enrichment,but when the conditions of source rocks and caprocks are good,natural gas with poor physical properties can also be accumulated.The direct caprock plays a major role in the rich and integrated natural gas reservoir,and the controlling effect of the regional caprock is not obvious because it is far away from the gas reservoir.