Research on Pre-stack High Precision Density Inversion: A Case Study on Lower Cambrian Longwangmiao Formation Gas Reservoir, in the GM Area of Sichuan Basin

The Longwangmiao Formation gas reservoir in Sichuan is a large-scale marine carbonate gas reservoir discovered in China, which controlled by various factors such as structures, faults and fractures. The strong heterogeneity, rapid lateral changes and complex gas-water relationships affect the production capacity construction of the block. Thus, it is necessary to study the reservoir characteristics and the gas-water distribution. The rock physical analysis of multiple well sections in the research area shows that the gas bearing reservoirs have low P-S wave velocity ratio, low density and low P wave impedance. Density parameter is a sensitive elastic parameter for effectively identifying high gas bearing reservoirs. The accurate density inversion results could lay a good foundation for the precise description and quantitative prediction of gas reservoirs. In the study, the objective function of the coefficient matrix for density inversion was improved, and the contribution to the objective function was quantitatively weighted using Mohs distance instead of Euclidean distance. The new method effectively improves the problem of ill conditioned coefficient matrix in the density inversion process and obtained more accurate density inversion results. The research results indicate that the central part of the main area of the Longwangmiao Formation gas reservoir in the GM area exhibits low density values and good gas bearing properties of the reservoir. The research results are highly consistent with the actual logging results, effectively support the efficient development of the Longwangmiao Formation carbonate gas reservoir in the study area.