Research and Application of “Time-, Frequency- and Amplitude-Preserved” Seismic Response Mechanisms of Short-Range Wavefields in Ultra-Deep Carbonate Reservoirs

Abstract

AbstractThe northwestern Sichuan Basin has high structural complexity, and the Lower Permian Qixia Formation is seen with low seismic structural imaging accuracy, inaccuracy for the reflection time position of stratum interfaces and the stratum time thickness, and the low vertical and horizontal resolutions of thin reservoirs. Given this, this paper, based on the prestack common reflection point (CRP) gather, investigates the prestack seismic response mechanism of dolomite reservoirs in the Qixia Formation, the Shuangyushi area of Northwest Sichuan. It is shown that the short-range wavefield is characterized by the time-preserving, frequency-preserving and amplitude-preserving capabilities. First, the time thickness of strata between the top and bottom reflection interfaces is the actual stratum time thickness with the highest fidelity, in the case of the small offset short-range wavefield of normal or nearly-normal propagation for the CRP gather. This characteristic preserves the intrinsic true stratum time thickness, which is called “time-preserved” for short. Second, the transverse propagation distance of the normal or nearly-normal propagating seismic waves is very short, leading to the least loss of intrinsic high-frequency components of seismic waves. Hence, this characteristic preserves the intrinsic high-frequency components and thus is called “frequency-preserved” for short. Finally, the short transverse propagation distance of normal or near-normal propagating seismic waves result in the highest reservoir resolution, and the tuning effect of the seismic waves produced by the recognizable reservoir and the loss of the high-frequency components are the lowest in this case. Therefore, the intrinsic amplitude of the reservoir seismic response containing the short-range highest frequency components is preserved to the most extent, which is called “amplitude-preserved” for short. All these characteristics are applied to the seismic data processing for the Shuangyushi area of Northwest Sichuan and the resultant good application performance indicate that the structure imaging quality and the resolution of reservoirs in the Qixia Formation are both improved significantly.KeywordsSichuan BasinShuangyushi areaTime-preservedFrequency-preservedAmplitude-preservedSeismic data processing