Seal potential of shale sequences through seismic anisotropy: Case study from Exmouth Sub-basin, Australia

Abstract

Sedimentary rocks with sealing potential can cap a reservoir by impeding the upward movement of hydrocarbons. An effective seal should have three qualifying factors of geometry, integrity, and capacity. Mapping seismic horizons and faults across the area of study reveals much about the geometry and integrity of the sealing unit. Capacity, however, depends on capillary pressure measurements of core and cuttings samples. Modeling capacity of seals away from and between wells has traditionally involved simple gridding techniques or association with most likely geologic or seismic facies. We have developed a different approach in using seismic data and applying it to the evaluation of sealing potential. Shales are the most common seals in petroleum systems. Seismically, well-developed shale units that have undergone compaction are likely to be anisotropic and are typical vertical transverse isotropic media. Seismic data with suitable acquisition parameters were processed to extract Embedded Image and Thomsen’s parameters of weak seismic anisotropy, tied to the vertical seismic profile data at wells. The spatial distribution of Embedded Image has shown a good correlation with capillary measurements of well samples. Hence, 3D modeling of epsilon was used as a weight factor to guide the capillary pressure (Embedded Image) values away from the wells. Capillary pressure values were then mapped on the fault planes to high grade the analysis of sand-shale juxtaposition. Our results helped to explain the distribution of successful wells and dry holes within the study area.