Use of geostatistical modeling to improve the understanding of permeability upscaling in isotropic and anisotropic burrowed reservoirs

Abstract

Coarse materials filling burrows in reservoirs can provide permeable pathways through an otherwise impermeable host rock matrix —thus enhancing fluid flow properties. However, understanding permeability anisotropy and permeability-upscaling under such conditions represents a challenge in the exploration and development of reservoirs. Herein, we examined 75 hypothetical models that represent diverse types and amounts of bioturbation. The aim is to understand the impacts of burrows on petrophysical characteristics, including upscaling of permeability where the matrix is isotropic. These models were simulated in a high-resolution 1-m3 grid (8 × 106 cells) using multipoint statistics (MPS) modeling techniques to systematically vary burrow morphology and bioturbation intensity in the same host rock matrix. The modeled burrow morphologies (vertical, horizontal, and boxwork morphologies) and bioturbation intensity―expressed as burrow percentage (BP, ranging from 2% to 50%)― show burrow connectivity trends increasing with increasing BP. In each trend, there is a burrow-morphology-dependent critical BP at which burrows develop connected permeability pathways. Accordingly, three unique patterns of burrow connectivity were identified among the 75 models. These include when burrows are: 1) just isolated volumes (isotropic system); 2) create unidirectional flow (anisotropic system); and 3) create omnidirectional flow (isotropic system). These connectivity patterns determine whether the permeability of the burrow-related reservoir is isotropic or anisotropic. Thus, identifying each of these connectivity patterns in burrowed reservoirs would help determine the appropriate averaging method to upscale permeability. The results of this study bridge an essential gap in reservoir modeling and simulation of hydrocarbon reservoirs and aquifers with burrowed strata.