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Abstract

The directional flow properties of a reservoir are very important for the design of reservoir development and waterflooding For a reservoir with natural fractures, the permeability is controlled by the preferred orientation of the fractures. This paper presents the results of an investigation for determining the fracture orientation from interference tests. The pressure response is analyzed based on the double porosity model proposed by Warren and Root. The calculations are performed numerically by use of Stephest Laplace inversion transform. The results show that the transition flow period depends not only on the fracture flow parameters, but also on the distance between the observation well and the active well. Based on this characteristic, a new method is presented to determine the fracture orientation and permeability components as well as the fracture-flowing parameters.

Introduction

A distinct characteristic of a naturally fractured reservoir is the "double-porosity" behavior - intergranular (primary) porosity and fracture (secondary) porosity. The main difference between the two porous regions is the contrast in storage and transport capacities. The intergranular pores have high storage, but low flow capacity, while the fractures have low storage, but high flow capacity.

Pressure transient response of a well in a naturally fractured reservoir is studied by many investigators. The fundamentals are based on double porosity model, a concept originated by Barenblatt et al and mathematically realized by Warren and Root. In deriving the mathematical expressions for the wellbore pressure, Warren and Root idealized the rock with fissures by a material with primary porosity contained within a systematic array of identical blocks, and the secondary porosity contained in uniform fractures orthogonal to each other and parallel to one of the principal axes of permeability. Two parameters, intraporosity flow factor, and w, storativity ratio, are commonly used to describe the double porosity behavior.

It is very common that fractures are more dominant in one direction than another.

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