Use of Single-Well Test Data for Estimating Permeability Anisotropy of the Naturally Fractured Spraberry Trend Area Reservoirs

Abstract

In order to fully understand the performance of waterflooding in Spraberry Trend Area reservoirs, large scale reservoir simulation using a dual-porosity simulator is necessary. The most important input data required by the simulator is the directional fracture permeability and the anisotropy of the reservoir permeability. This paper reports a new method for estimating directional fracture permeabilities from pressure data recorded during single-well tests. In this study, a new, dual-porosity, dual-permeability, mathematical model has been developed for single phase flow in reservoirs that are naturally, vertically fractured. Fracture spacing is explicitly considered in the model. The model consistently fits a set of single-well-test data obtained from a Spraberry well before and after hydraulic fracturing. The on-trend and off-trend fracture permeabilities before hydraulic treatment have been estimated to be k x = 30 md and k y = 0.09 md, respectively. The anisotropy of the fracture permeability is k x / k y = 322. The on-trend and off-trend fracture permeabilities after treatment have been estimated to be k x = 39 md and k y = 0.9 md, respectively. The anisotropy of the fracture permeability is k x / k y = 43. These results indicate that the hydraulic fracturing treatment significantly improved (10 fold) fracture permeability in the off-trend direction. This paper provides reservoir engineers with a useful tool for estimating fracture permeability anisotropy and other properties of naturally fractured reservoirs from single-well tests.