Study On Sedimentary Facies Characteristics Of Ma5₁₊₂ Of Majiagou Formation Of Ordovician And Its Control Of Gas In Qiaozhen Area

Currently exploration and production data indicate that the Ma5₁₊₂ formation of the study area have great potential to generate gas reservoirs and become the focus formation of further exploration,and previous studies show that the sedimentary facies related closely with natural gas enrichment.Therefore,it has great significance to study the sedimentary facies of the field to gas development.The stratigraphic division of Ma5₁₊₂ formation were conducted based on outcrop and core observation,drilling and logging data,marker bed and logging trace,which is divide into six sublayers,compare with the East area,the West area denuded seriously.reservoir rocks in the area were mainly dolomite while reservoir pore were solution pores,intercrystalline pores,intergranular solution pores,gypsum mould pore and cracks,physical property was ultra low porosity and ultra low permeability.The test data was analyzed to identify the precipitation facie of Qiaozhen area as restricted platform subfacies and tide-flat,which can be subdivided into dolomitic flat,argillaceous dolomitic flat,dolomitic-limemud flat by the composition of deposition,then draw the phase diagram of precipitation microfacies based on sublayer.the ancient palaeogeomorphology was revived by results of “impression method” and “residual thick”.The area is mainly located in karst slope that has intense denudation,thus various types of secondary porosity and dissolution cavities were formed.Most of microfacies in the aera was dolomitic microfacies,due to the development residual grain structure dolomite,powder,fine crystalline dolomite lithologies in the dolomitic flat,thus varieties of emposieu systems can be formed through denudation,which means sedimentary facies provides favorable reservoir space for the formation of natural gas.Through the effective thickness data analysis and gas test data,the results indicate that dolomitic microfacies have the largest effective thickness and well gas test results.Therefore,sedimentary facies has some control functions on natural gas.