Comprehensive Evaluation Of Tight Sandstone Reservoir- An Example From Shanxi Group,Linxing Block

The Linxing block is consisted of tight sandstone reservoirs with low-porosity and low-permeability,characterized strong heterogeneity and complicated pore throat network connections,therefore,accurate evaluation of tight sandstone reservoirs needs to be improved,since current result of oil and gas exploration from them are not satisfactory.The next question is how an accurately evaluation of tight sandstone reservoirs can be established.This is also a major problem that oil industry in most oilfields is facing to further optimize the recovery potential from tight sandstones.This study provides a detailed discussion about the reservoir description of tight sandstone reservoir of Shanxi formation in linxing block.Based on previous researches on tight sandstone,this study incorporates vertical and sidewall core observation,petrophysical log analysis,casted thin sections and scanning electron microscope data,investigates facies characterization and their 3D distribution,identifies the relation between lithofacies and their corresponding elements of petroleum system,and finally establishes pore structures within reservoirs.Quality of the source rock,reservoir and engineering is analyzed to define the lower limit of reservoir's physical property and its effective thickness.Porosity and permeability of cored reservoir,brittleness of sandstone,single layer effective thickness,gas-bearing property and physical property within tested sections are evaluated using weighted average evaluation(assigning different values for each layer).A set of reservoir evaluation criteria suitable for the study area is proposed,the reservoir can be divided into dry layer(scour lower than 0.629),non-industrial gas flow(score in the range of 0.715~0.79),low-yielding gas layer(score in the range of 0.715~0.79,and medium-to high-yielding gas layer(scour greater than 0.79).Based on the development of fracture in outcrop profile,the fracture development within the prolific reservoir is studied,which clarifies the relationship between prolific reservoir and fracture development.The prolific reservoirs in linxing block generally have well-developed fractures which are especiallywell-developed in areas with strong tectonic activities.Dominant medium-coarse grained sandstone were deposited under strong hydrodynamic conditions,and there is a negative correlation between fracture density and single-layer sand thickness Fractures are developed the most in the lithofacies consisting of thin sand layer,thin coal layer and mudstone.The high-quality reservoirs are located in areas with well-developed fractures,and the sweetspots of tight sandstone reservoir tend to be found in the main body of lenticular channel system.