Velocity model estimation of karstic fault reservoirs using full-waveform inversion accelerated on graphics processing unit

Abstract

The karstic fault reservoir is a type of hydrocarbon-enriched carbonate reservoir. It is a combination of small-scale caves, vugs, and fractures developing near deep-seated faults, which makes it difficult to delineate using traditional seismic imaging methods. Recent research on geologic characteristics of paleokarst reservoirs facilitates hydrocarbon exploration and exploitation in western China. To interpret karstic fault systems and reservoirs, the seismic image is an effective tool. A high-quality velocity model is essential for high-resolution migration. These seismic results contain crucial information to interpret reservoirs. Full-waveform inversion (FWI) is a powerful method to obtain high-precision velocity models because it makes use of the kinematic and dynamic information in the seismic full wavefield. To image such complicated and irregular fractured-cavity reservoirs accurately, we have applied a multiscale FWI method accelerated on graphics processing unit devices to fault-controlled paleokarst reservoir models. According to the model test results, FWI shows high performance in delineating the boundaries of fault-controlled karstic reservoirs. The proposed method also has the potential to characterize inner structures. Based on the high-precision velocity model provided by FWI, the seismic image obtained by reverse time migration is also improved. These seismic results will show the location, width, and shape of the fault-karst structure, which gives detailed information for fault-controlled paleokarst reservoir interpretation.