High-Resolution Seismic Inversion Pinpoints Ultra-Thin Shale Interbeds and Sweet Spots

Abstract The W block shale in the study area is located at the West Canada basin and belongs to the low-porosity and ultra-low permeability gas-condensate reservoirs. The sandwiched layers in the shale are extremely important for reservoir reconstruction. As the single-layer thickness of the carbonate interbeds in the W block shale is very thin and have multi-stage superposition characteristics, the use of conventional geostatistical inversion cannot effectively and accurately predict the thin sweet spots and interbeds in the shale. This article uses three-dimensional probability constraints as pre-stack geostatistical inversion to replace traditional one-dimensional and two-dimensional face constraint inversion and achieved quantitative prediction of interbeds using well logging and 3D seismic data, so that prediction outcomes fully integrates well logging, seismic data and established a set of 3D probability constraint pre-stack geostatistical inversion process for thin interbeds and sweet spots in the shale. The process mainly includes the following crucial steps: (1) Well logging evaluation of shale reservoir parameters, analysis of shale rockphysical parameters and analysis of petrophysical characteristics of shale sweet spots and carbonate interbeds from well data, in order to evaluate and use seismic data to predict the possibility of shale sweet spots and interbeds. The characteristics of shale sweet spots is low Poisson ratio, moderate Young's modulus, high total organic content (TOC) and high brittleness. The characteristics of carbonate interbeds is high Poisson ratio, high Young's modulus, low TOC and high density. (2) Pre-stack gather optimization to establish six reliable partial sub-offset seismic data volumes. (3) Application of waveform difference simulation for prediction of shale interbeds, analysis of the vertical and horizontal variation characteristics of the interbeds based on post-stack seismic data and the three-dimensional probability volume of carbonate interbeds was estabilished according to the results of seismic waveform difference simulation and well logs. (4) High resolution 3D lithologic probability constrained pre-stack geostatistical inversion are performed and effectively predicted the spatial variation characteristics of shale thin interbeds and sweet spots.