Gas detecting of the Lower Permian dolomite reservoirs in Sichuan Basin using amplitude ratio attribute of PP-wave to PS-wave

Abstract

At present, multi-wave multi-component seismic exploration has a good effect in the gas-bearing structural imaging improvement, fracture detection, clastic rock lithology description, reservoir monitoring, etc., but in gas detection, especially for the deep carbonate reservoir, there are not many successful cases. The paper takes the 5000m deep Lower Permian Qixia Formation dolomite gas reservoir in the central part of Sichuan Basin as the research target. Aiming at the differences in gas production characteristics of different wells and difficulty in gas detection, based on the high-precision matched 3D multi-wave seismic data by seismic processing and fine horizon interpretation of target formation, the differences between the PP- and PS-wave reflection amplitudes of high-production wells, low-production wells and poor gas wells are compared and analyzed, and multi-wave forward modelling and analysis are carried out. It is clear that the high production gas layer has the characteristics of strong PP-wave reflection and weaker PS-wave reflection. With the gas production decreasing from high to low, the reflection amplitude of PP gradually weakens, while that of PS change little and nearly have no obvious abnormalities. Finally, attribute of amplitude ratio of PP to PS were extracted for gas detection, which is in good agreement with the gas characteristics of the known wells and consistent with current geological understanding. The amplitude ratio attribute of PP to PS could provide a quick and reliable gas detection method for the deep dolomite reservoir.