Facies-based Bayesian simultaneous inversion technology and its application: A case study of the north section of No.5 fault zone in Shunbei area, Tarim Basin, China

The fault-karst carbonate reservoir in the Shunbei area of the Tarim Basin is controlled by deep strike-slip faults and forms a fault-karst system. The reservoir space primarily includes holes and fractures, and its strong anisotropism aggravates the complexity of the reservoir seismic response characteristics. High-quality reservoirs in the fault-karst body in this area have different burial depths, which is not conducive to the establishment of low-frequency models in traditional inversion. Facies-based Bayesian simultaneous inversion technology combines Bayesian classification with pre-stack simultaneous inversion, divides different facies based on multi-elastic parameters such as P-wave and S-wave velocity and density, and conducts an in-depth trend analysis for each phase to establish the initial model. Compared with traditional inversion technology, this technology not only improves the inversion accuracy but also increases the stability of the density inversion. Taking the carbonate fault-karst body in the northern section of the No.5 fault zone in the Shunbei area as the research object, combined with the actual production situation, two facies, fractured-cavity limestone, and tight limestone, were divided by elastic parameters and then subjected to depth trend analysis and inversion. Through the single fracture-cavity equivalent model test and practical application analysis, the density data obtained by the Facies based Bayesian simultaneous inversion were highly consistent with the reservoirs drilled by Wells W3 and W3C in the northern section of the No.5 fault zone, which verifies the applicability and reliability of the inversion technique in the study area and the reliability of the results.