Research On Seismic Method Of Coalbed Methane Sweet-spot

At present,proven coalbed methane reserves are about 37,000 cubic kilometers in china,which is close to one-third of proven conventional natural gas reserves.Therefore,coalbed methane has huge exploration and utilization value.The sedimentary environment of the main coal measure strata in Fengcheng coalbed methane block is the transitional facies deposition of marine and continental facies,while the sedimentary environment of marine and continental facies changes rapidly,and the geological characteristics of the strata developed in different depositional environments are different,mainly manifested in the small thickness of the single layer,poor continuity,and difference in the abundance of organic matter.the coalbed has problems such as thin thickness,different coalbeds in different structural parts,strong heterogeneity,and obvious differences in the distribution of coalbed methane.Therefore,it is necessary to find the coalbed methane "sweet spot" with thick coal seam and high gas content in the study area.perform petrophysical analysis on the existing logging data to determine the relationship between lithology-physical properties-gas-bearing properties and geophysical parameters,further inversion of target reservoirs,lithology prediction and quantification of oil and gas detection results.In view of the thin thickness of the coal seam,the post-stack facies-controlled chaos inversion was used to study the spatial distribution of the coal reservoir,and the seismic inversion was controlled by the seismic facies to reduce the multiple solutions.The regularization factor is controlled based on Bayesian theory,so that the resolution and stability of the inversion results are unified.The gas-bearing property in coal seams is studied by using the seismic property of fluid activity property.Based on the seismic propagation theory and the calculation formula of fluid activity properties,the MP algorithm based on WVD is used to perform highprecision time-frequency analysis on seismic data,so as to obtain fluid activity properties.The above method was applied in Jiangxi Fengcheng coalbed methane block,and the spatial distribution of the target coal seam in the study area was characterized by the inversion results.Combined with the coal thickness predicted by post-stack reservoir inversion,the fluid activity attribute was used to predict the gas-bearing properties of coal reservoirs,The predicted thickness and gas content are in good agreement with the logging interpretation.Finally,the coalbed methane sweet spot area in the study area is selected based on the thickness of the coal seam and the gas-bearing property of the coal seam,combined with the preservation conditions of the coalbed methane in the study area and the engineering conditions.