Study On Formation And Controlling Factors Of Tight Sandstone Reservoir In Shanxi Formation Of Linfen Mountain

In the CMB(Coal Bed Methane) exploration process of Linfen, Shanxi, the gas logging of plenty exploration wells indicates a good exploration prospects in the tight sandstone which is above and below the coal stratum. However the reservoir has the characteristics of rock density and poor physical property, which makes exploration and development hard. As for the reservoir in the research area of Shanxi formation, we use petrology, reservoir geology and sedimentary facies theory as a guide, combining with the analysis of the core and the experimental results, logging data and the regional geological background, making full use of the casting thin sections identification, scanning electron microscopy (SEM), X-ray diffraction analysis, cathodoluminescence, temperature test of the fluid inclusion, analysis of capillary pressure. We systematic studied sandstone reservoir characteristics, sedimentary environment, physical characteristics of Shanxi formation, and focus on the pore structure, the diagenesis and the controlling factors of the compaction of the reservoir, preferably selected the evaluating parameters of the tight sandstone reservoirs, and carried on a comprehensive geological evaluation and a prediction of favorable reservoir, provided the practical guidance for next exploration deployment.The Shanxi formation of study area is about120m thick. The direction of the distribution is north-south. The scale of the single sand body is small, and lateral variation is big. Compound sand body is thin. Petrological analysis shows the rock type of Shanxi formation tight sandstone reservoir is medium-fine grained lithic sandstone, low feldspar content, medium sorting, psephicity from subangular to sub-rounded, point line contact relationship, basal cementation. The tight sandstone of Shanxi formation have ultra low porosity and permeability, pore types mainly include intergranular pore, dissolved pore, intercrystaliine pore, micro pore, micro cracks, the mercury injection indicates the pore structure is poor, generally, the structure type is small pore and micro throat.The Shanxi formation of study area is mainly transitional lacustrine deltaic depositional system. The sandstone is mainly distributed in distributary channel of deltaic plain and underwater branch river of prodelta. The reservoir of Shanxi formation has undergone complex diagenesis, compaction, cementation, dissolution and metasomatic alteration and recrystallization. The diagenetic evolutionary stage belongs to stage B of middle diagenesis phase.The characteristics of density and poor property of the reservoir is controlled by rock structure composition, grain size and sorting, sedimentary facies and diagenesis. Distributary channel and underwater distributary channel microfacies are favorable. In all types of diagenesis. kaolinization and dissolution is constructive diagenesis on porosity, compaction siliceous cementation, filling and metasomatism do damage to the reservoir property. Compaction makes primary pore disappearance, and makes porosity and permeability lower. Cementation do further deterioration to physical properties. Dissolution can form secondary solution pores, and improves the tight sandstone reservoir performance.Combining macroscopic and microscopic characteristics of tight sandstone reservoir, it is determined the reservoir evaluation and classification standard of Shanxi formation. It is divided into four categories, including common development â…¡ medium and â…¢ poor reservoir. It is predicted that favorable reservoir belt distribute in central and northern sandstone body.