Seismic Data-Driven Rock Physics Models and the Application to Tight Gas Saturation Estimation

摘要

Pore fluids prediction using seismic data is seldom covered in most considerable discussion in tight gas, although more interests are focused on fractures and sweet spots. Some theories based on homogeneous high porosity and permeability rocks have been widely investigated. Unfortunately, there seems to be no models published can properly describe the nonlinear relationship between saturation and P wave velocity at seismic frequency in tight reservoir, and low frequency experimental data are still scarce. Gases always tend to gather at upper pore spaces in reservoir, resulting in saturation variation with depth due to interaction principle between buoyancy and capillary pressure. This law hence encourages us to probe into partial saturation related elastic properties through seismic data mining incorporating with experimental and logging data to indicate fluids. Through various gas intervals oriented P wave-‘saturation’ data collections extracted from seismic data, new nonlinear relations are discovered, which indicate coexistence of patchy and homogeneous fluids effects, and cannot be properly explained by published models. Motivated by the complex relations of Vp-Sw at seismic frequency, a modified White’s model is proposed to explain partial saturation effects in tight rocks, and updated rock physics models match the real seismic data quite well. Case study of tight gas exploration in a Triassic basin in southwest China shows that seismic data-driven models are helpful means to reduce uncertainly in seismic interpretation and have improved the success rate of drilling by 20%.