CBM Accumulation Effect And Logging Identification Of Dominant Reservoirs In Zhijin Area

According to the characteristics of multiple coal seams,uneven thickness,uneven coal seam spacing,complex coal structure,and uneven gas content in ZhiJin area,the study has clarified the sedimentary evolution characteristics of the area through geological survey,experimental testing and data analysis,and further studied the effect of coalbed methane accumulation in this area from four aspects: sedimentation,hydrology,structure and burial depth.Combined with the existing coring and logging data,a coal structure index model suitable for Zhijin block was established.Prediction of the coal seam of the ZhuZang subsyncline test well group for which the coal body structure has not been determined,combining coal seam thickness,coal seam gas content,coal seam depth and coal seam ash,the dominant reservoirs in the range of the ZhuZang sub syncline test well group were selected,which provided a reference for the subsequent exploration and development of coalbed methane in this area.The delta-tidal flat deposition system was mainly developed during the coal accumulation period of the Longtan Formation in the Late Permian in ZhiJin area.Due to the seaward and retreat of the Longtan Formation,the upper and lower sections of the Longtan Formation in the vertical direction were tidal flat deposition,and the middle section was delta deposition.The complex and changeable sedimentary environment in ZhiJin area has formed deltatidal flat type,lagoon-tidal flat type coal accumulation.The combination of coal seam roof and floor in this area was mainly composed of mudstone and fine-grained sedimentary rock with good sealing property.The sedimentary environment provided good material foundation and preservation conditions for coalbed methane reservoir.The tectonic action in this area affected the gas content of coal seams to different degrees,open faults would accelerate the escape of coalbed methane.Closed faults and the syncline axis were beneficial to the preservation of coalbed methane.At the same time,the syncline axis would form a local water retention area,which would enhance the sealing properties of coalbed methane.The coalbed methane enrichment and accumulation in Zhijin block can be summarized as: sedimentary coal control,combined structure-hydrology-buried depth gas control.Using logging data of Zhijin block,SPSS software was used to optimize logging parameters,combined with the positive and negative relationship between the parameters,a CSI model of coal structure index suitable for the area was established.And predicted the test well group in the area of the ZhuZang sub-syncline where the coal body structure has not been clarified.According to the obtained coal structure index CSI,combining normalized coal seam thickness,coal seam gas content,coal seam depth and coal seam ash parameters,using gray correlation analysis method to screen out the eight-layer dominant reservoirs in ZhuZang subsyncline test well group 6#,7#,16#,17#,20#,23#,27# and 30#,and 2 #,8 # and 15 # were the secondary dominant reservoirs.