The Accumulation Characteristics Of Tight Gas Reservoirs In The Upper Palaeozoic Of Eastern Ordos Basin

The natural gas reservoirs of Upper Paleozoic in the eastern Ordos Basin have the characteristics of low porosity,low permeability,lowabudance,widespread distribution and so on.The Yulin gasfield,zhe Zizhou gasfield,the Mizhi gasfield and the Shenmu gasfield are all included in this area,and their exploration potential is huge.On zhe basis of previous studies,this paper,basing on zhe logging and core observation,various laboratory analysis and the data of test gas,integrately using the latest the oretical basis of oil and gas geology,reservoir geology,reservoir geochemistry,fluid history knowledgeand the reservoir dynamics,make the geological comprehensive analysis and state-of-the-artexperimental analysis techniques combined,the moden characteristics and zhe historical analysis combined,staticstudy and dynamics study combined.In the paper,it mainly studies the basic characteristics of the gas reservoir,and on the basis of these studing it comprehensively analyses the upper Paleozic gas enrichment rules and discusses the Upper Paleozic gas reservoir types.Finally it reaches the following keys understanding:(1)The controlling effect of the gas generating intensity on the reservoir combinations in the lowereastem part of the basin is not obvious,but it plays an important role in the middle eastern part of the basin.The area of high gas generating intensity values product gas,while those low value area product water,which indicates that the gas generating intensity is one of the main contolling factors of the gas water disteibution in the study area.(2)In the studing area,the Upper Paleozoic source rocks in the Early Jurassic reaches its low maturity stage.The Late Jurassic-Early Cretaceous is the time that gas produced greatly,and gathered into accumulation.From the He-8 layer and Taiyuan group,we can see that there servoir densified first,and then the natural gas concentrated,while in the Shan-2 layer the reservoir densifying and natural gas concentration are at the same time.(3)The physical property of reservoir have some controlling effect on the gas production,but the degree of influence of each reservoir is not the same.(4)In eastern Ordos basin,the reservoir storage coefficient of the major gas-bearing beds in upper palaeozoic is mainly controlled by these factors such as particle diameter,the intensity of dissolution,silica particles content,porosity,permeability and median pore throat radius.(5)In eastern Ordos basin,the upper palaeozoic gas accumulations supposed to be quasi-continuous pools.The main features are as follows:gas distributes continuously in large areas without clear gas reservoir boundary;the distribution of gas and water is complex and has no obvious edge and bottom water.The distribution and enrichment of natural gas is mainly controlled by the conditions of gas source and reservoir.