Study Of Coal Seam Methane Geological Conditions And Sandstone Gas Reservoir Characteristics In Southeast Edge Of The Ordos Basin

The study area is located in Hancheng-Chengcheng region,in the southeastern margin of the Ordos Basin.The Hancheng region is the key block of the Ordos Basin for coalbed methane(CBM)development,preliminary exploration showed that the region is rich in CBM resources,gas showings can also be found in roof sandstone.Based on the existing coal field geological data of Hancheng-Chengcheng mining area,new drilled coalbed methane wells,outcrop observation and other relevant information,and guided by the theory of sedimentology,coalbed methane geology,structural geology and reservoir sedimentology,geological structure,coal-bearing sedimentary environment,coal-bed development feature,developmental characteristics of coal petrography and coal quality,and developmental characteristics of sandstone and mudstone have been analyzed completely.Occurrence characteristic of CBM and sandstone gas has been discussed in order to outline favorable exploration areas.The core content is as follows:1)In the research area,the coal series in late Paleozoic were mainly developed in epicontinental-coastal plain environment.Based on the observation and description of cores and rock debris,combined with outcrops of Carboniferous-Permian in and around the study area,four major depositional systems has been identified,which are carbonate platform,barrier-lagoon,shallow delta and fluvial system respectively.Coal measure strata of the region show a sedimentary sequence of continental facies-marine-terrigenous facies-continental facies.In Taiyuan-Shanxi section,six sedimentary cycles can be identified,the main coal seams are developed in the top of C2-1 and C2-3 cycle.2)With the study of individual well,well tie section and structural characteristics of the study area,the distribution and burial depth of coal-bed has been investigated,the seam thickness and depth contour map has been made.By observing coal polished section through microscope,the features of organic components,pore types and pore structure in coal has been determined.According to the analysis of gas-bearing properties,combined with structural characteristics,seam thickness and mudstone caprock thickness,the gas control factors were analyzed.All these elements are made to evaluate the coal seam gas generation and reservoir properties.3)The sandstone and mudstone of the second member of Shanxi Formation,the upper mudstone of the No.11 coal seam of Taiyuan Formation were analyzed by the use of existing well data.According to the analysis of sandstone components,sandstone pore structure and sandstone fracture,combined with the test data of sandstone samples,the sandstone reservoir in the study area are confirmed as middle-low permeability reservoirs.4)According to the distribution of two main coal seams,sandstone and mudstone in study area,under the control of the preferred conditions,favorable zone of each coal seam and sandstone has been outlined independently.Finally,the most favorable exploration target of CBM and sandstone gas has been optimized under the control of all the favorable zones.