Applicability Analysis of Log Calculation Method for Organic Matter Maturity of Changning Shale Gas Reservoir in Southern Sichuan Basin
The shale formation of Wufeng formation and Longmaxi formation in southern Sichuan are affected by sedimentation and uplift caused by multi-stage tectonic movement,which makes the degree of thermal evolution in different regions very different.The maturity of organic matter is an important parameter to evaluate the degree of thermal evolution of shale gas reservoirs.Based on the data of geochemistry,laser Raman,asphalt reflectance,physical properties,gas content test and logging curve,the thermal evolution characteristics of organic matter in well shals with different maturity levels in Changning area of south Sichuan were studied,and the sensitive logging responses under different maturity ranges were determined.The calculation methods of equivalent vitrinite reflectance(RO)by deformation ΔlogR,multiple regression and CatBoost algorithms for different maturity types of wells are established,and the calculation results and applicability are compared.The results show that:① Based on the difference of the thermal evolution characteristics of organic matter before and after graphitization and the influence on the sensitive resistivity curve,the two types of overmature stage I and overmature stage II are divided into the lower limit of graphitization RO of 3.5%.② The characteristics of over-mature stage Ⅰ are high porosity,low water saturation,high gas content,high resistivity value,weak overlap difference between resistivity curve and sonic time difference curve,and the color combination of Rt-AC logging curve is"purple+red"mode;The characteristics of overmature phase II are low porosity,high water saturation,low gas content and low resistivity.The overlap of resistivity curve and acoustic time difference curve is obviously different.The color combination of Rt-AC logging curve is"blue+dark red"mode.③CatBoost algorithm selected GR,AC,CNL and Rt curves as input variables,and the correlation coefficients between the calculated RO values and the measured RO values of maturity wells Ⅰ and Ⅱ were all more than 0.95,which achieved a good prediction effect of organic matter maturity.This method makes up for the discontinuous experimental data to a certain extent,and provides a basis for identifying the thermal evolution stage of shale gas reservoirs and reducing the risk of exploration and development.
the southern Sichuan basinshale gas reservoirgraphitizationmaturity of organic matterlog calculation method
万方数据
维普
