Marine-Terrigenous Shale Reservior Evaluation And Characterization

A total number of 12 drill core shale samples are analyzed by conventional experiments such as observation,X-ray diffraction,Rock-Eval,Ro reflection,organic geochemistry biomarkers,macerals,SEM,porosity and permeability,along with unconventional methods as low temperature nitrogen and carbon dioxide gas adsorption,NMR and X-CT scan,establishing an evaluation system for marine-terrigenous shale reservoir.Two sets of shale gas potential strata are developed in Linxing research district,Shanxi Formation of Lower Carboniferous,and Taiyuan Formation of Upper Permian.The former is terrigenous delta mudstone deposit including dark color calcareous mudstone and silty shale,and the latter is shallow marine environment including dark black shale intercalated with thin siltstone.Taiyuan shale generated more hydrocarbons and has higher amount of in-situ hydrocarbons.Total organic carbon of these two formations are 0.95?26.86wt%,with an average value of 5.98wt%.Ro is 1.26?1.79%,in the stage of high maturity,with a majority of type III kerogen type.Total HC of Taiyuan rocks is relatively low but with a higher value of bitumen,indicating that the low grade aquatic organism and algae source organic matter of Taiyuan formation are more than that of Shanxi Formation.Quartz and clay minerals are the majority minerals of the reservoir rock components.Micro cracks and large pores can be found,average surface area of Shanxi formation is less than that of Taiyuan formation,but with a larger average pore volume and pore diameter.Micro and medium pores are the predominant types in reservoir's pore system,and contribute most space for adsorbed gas.Total pore volume and surface area rapidly increase along with the decrease of pore diameter.NMR and X-CT scan are supplementary methods to low temperature nitrogen and carbon dioxide gas adsorption,the synthesis of NMR and low temperature gas adsorption shows reasonable pore distribution,but the latter is more specific and accurate.Based on the stratum characterization and the above experiments and analysis,Taiyuan formation can be seen as a more potential reservoir.