Research On Well Logging Evaluation Method Of Tight Sandstone Gas Reservoir In Xujiahe Formation In DY Area Of CX Depression

With the depletion of conventional oil and gas reservoir resources,unconventional reservoirs such as tight sandstone have gradually become the main focus of oil and gas development.Tight sandstone reservoirs are widely distributed in China and have good prospects for exploration and development.However,compared with conventional reservoirs,tight sandstone reservoirs are characterized by complex lithology,poor physical properties,and irregular fluid distribution,which pose significant challenges for exploration and development.In this paper,the main research object is the tight sandstone reservoir of the third member of the Xujiahe Formation in the DY area of the CX Depression in the Sichuan Basin.Based on previous research results,we address the current challenges of difficult lithology identification,large relative errors in physical property parameters,low accuracy of log interpretation,and inaccurate reservoir delineation.We integrate conventional well logging data,logging data,gas testing data,thin section observations,and core experimental data to analyze the reservoir,and develop a comprehensive well logging evaluation system for tight sandstone gas reservoirs,which includes complex lithology identification,physical property parameter calculation,fracture identification,fluid identification,and reservoir classification.In terms of lithology identification and porosity calculation,an equivalent component method(CRAE)based on conventional well logging,logging data,and thin section data is proposed.The rock framework parameters are determined using crossplot methods,and the lithology component content and porosity are calculated using core experimental data and thin section data as calibration.In combination with the established median grain size prediction model,the lithology categories of the entire interval and relatively accurate porosity values are finally obtained,the coincidence rate is 88.6%.In terms of permeability calculation,the relationship between porosity and median grain size is found to be highly correlated through the analysis of conventional well logging data and permeability.Combined with regional characteristics,a permeability calculation formula suitable for this interval is proposed using core physical property experimental data as calibration,and the lower limit of reservoir physical property parameters is analyzed.In terms of fracture identification,methods such as resistivity invasion correction ratio,three-porosity ratio,and fracture coefficient are tested,and the three-porosity ratio method is ultimately selected as the most applicable fracture identification method in this area.The three-porosity model is used to calculate the matrix porosity and fracture porosity of the formation.The geological characteristics of "cake-like" fractures and logging response characteristics are analyzed,and corresponding identification criteria are established,achieving good identification results,the coincidence rate is 81.2%.In terms of fluid identification,a fluid identification method based on bound water saturation is preferred.A regression statistical model for bound water saturation in the area is established,and Archie’s formula is used to calculate the water saturation,combined with bound water saturation,for gas-water layer discrimination.The method’s applicability is verified using well-testing results,the coincidence rate is 85.71%.In reservoir classification,based on the geological characteristics of the region and calculated reservoir parameters,a reservoir classification method for the three segments of the Xujiahe Formation in DY area is proposed.The reservoirs in the region are divided into four types,type I to IV,from good to poor,providing a basis for efficient exploration and development of the target interval.