Study On The Reservoir Characteristics Of The Ordovician Ma541 Member Of The Block Shaan231 In Ordos Basin

Jinbian Gasfield was the earliest and the most successful to develop in a large scale in Ordos Basin.As the greatest time of Gas/oil development of the Ordos Basin is coming up, it's urgent for Jinbian gasfield to stabilize and extend the production.The Ma5₄¹member of Ordovician is the one of the main producing reservoirs in the northern Jinbian gas field, Ordos Basin,so it is significant to study and evaluate the reservoir character.The object of this paper is the Shan231 Block of Jinbian Gas Field in Ordos Basin,on the basis of previous studies,guided by the relative theories of carbonate sedimentology, reservoir geology and diagenic metamorphism,and by the means of geological study,core description and laboratory testing,the properties,lateral distribution,the sedimentary characters of the reservoir and diagenic metamorphism have been fully studied.Shan231 block is located in the northwestern part of Jinbian peleoplatform,which is high in the northeast and low in the southwest.Karstification had the important impact on The Ma5₄¹member,due to the denudation the northwestern lost strata of Shan231 block made it unconformable to the Neopaleozoic Carboniferous System,not having been eroden by the paleogutter to the Ma5₄¹ member,the northwestern zone is the key factor of dominating the karstification of Shan231 Block.From the lost strata line the Ma5₄¹member has the southeastward thickening tendency,and it goes steady.Relating to the karstification,the physical properties of the reservoir are getting worse gradually from the lost strata line to the southeast.It developed three microfacies:the supratidal gypse-dolomite ground,the supratidal gypseous-dolomite ground and intertidal dolomite ground in the Shan231 Block. The supratidal gypse-dolomite ground of the Ma5₄¹member is the most favorable facies,the supratidal gypseous-dolomite ground is the second.Based on the preexisting data the producing pay is distributed in the Ma5₄^1a member.There are separate northeast-trending en echelon nose-shaped uplifts in the Shah231 Block.Therefore,the gas abundance zones of the Shan231 Block are influenced by several factors such as the formation thickness of the Ma5₄^1a member,the favorable structure,the physical properties,and sedimentary facies, generally the most favorable zones are distributed bindingly along the lost strata line,local changes of the gas abundance zones have been influenced by the factors such as the formation thickness of the Ma5₄^1a member,the top structural points and the physical properties.