Study Of Effect On Material Composition For Shale Reservoir Pore Heterogeneity

Lower Silurian Longmaxi Formation in south China,which is important stratum for shale gas exploration and development,has achieved commercial development initially in Fulin,Chongqin,but shale gas production in different area,well,stratum still has significant difference.Affected by geological heterogeneity,the research of micro pores heterogeneity which restricts reservoir evaluation and production prediction is insufficient.So this thesis takes W2 well for an example and Shale of Longmaxi Formation for research object.Based on data collection,drill documentation,experiment test,comprehensive research,this thesis studies material composition and occurrence characteristics in shale,pore characteristics and its heterogeneity,and effect on material composition for pore heterogeneity,and obtains the following results.W2 well exposes that the thickness of organic-rich shale of Longmaxi formation is 89.8m and its lithology includes silty shale,siliceous Shale,carbonaceous shale,and black shale.Sedimentary microfacies of Longmaxi Formation contain deep water silicon-mud shelf microfacies,deep water muddy shelf microfacies,deep water Sand-mud shelf microfacies,deep water mixed shelf microfacies,and shallow water mud shelf microfacies.Shale of Longmaxi Formation,I type kerogen,which total organic carbon content of 3.3% average value is in over mature stage which between 2.42%-2.97%.Minerals in shale contain quartz(average value 55.9%),clay mineral(average value 30.5%),feldspar(average value 3.08%),carbonate minerals(average value 5.92%)and pyrite(average value 3.94%).Material occurrence state in shale is complex,and they can divide several types based on SEM images.Total organic carbon content increase with the increase of depth vertically,and content of different mineral has obvious difference,which are affected by sedimentary environment.Using N2 adsorption,CO2 adsorption,SEM experiment analyzes pores in shale of Longmaxi Formation.N2 adsorption experiment shows that specific surface area in organic-poor shale is 2.5m2/g of average value,pore volume 0.0037cm3/g average value,and average pore size of 7.6nm.Specific surface area in organic-rich shale is 15.7m2/g in average value,pore volume 0.0125cm3/g average value,and average pore size of 4nm.CO2 adsorption experiment shows that micropores in shale have two peak pore size,0.45-0.65 nm and 0.85-0.9nm,specific surface area 10.934m2/g average value,pore volume 0.00188cm3/g in average value.SEM images show that pore types resulted from different material are various and have complex origin.Based on pore state,they can divide several types.Pore characteristics of different samples vertically show strong heterogeneity,which is controlled by total organic carbon content.Effect on material composition in shale of Longmaxi Formation for pores shows that mesopores and micropores are controlled by organic matter,and macropore is controlled by minerals.Specific surface area in organic-poor shale is mainly controlled by clay minerals.Specific surface area in organic-rich shale is mainly are controlled by organic matter,and with the increase of organic matter content,its pore contribution increase.The research of effect on material composition for shale reservoir pore heterogeneity can provide basis for exploration and development of Longmaxi Formation shale gas in Wuxi area.