Fractal Pressure-Transient Response of Fracture Networks

Abstract

Fractured reservoirs have received considerable attention over the last decade in geothermal reservoir engineering. Typical models for the analysis of pressure-transient test data generally rely on the 2D radial-flow model. However, a simple 2D model is often insufficient for the analysis of data from naturally fractured systems. It is required to consider complex boundary effects, double-porosity behavior and 1D and 3D models for the characterization of highly heterogeneous reservoirs. Recently, pressure-transient response of fracture networks with fractal structure was investigated by Chang and Yortsos (1990); and mathematical solutions for reservoirs of arbitrary dimensions were obtained. On the basis of their predictions, we interpreted falloff data from the injection tests of well YT-2 drilled in the Yutsubo geothermal field. Fractal structure is indicated by parallel linear plots of pressure and pressure derivative vs time on a log-log scale with a slope of 0.26. This fractal network of fractures (1.48<D<1.85) has radial structure around the well and is thought to be formed during cold water in-jection into a hot low-permeability formation.