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Abstract

This paper presents the transient pressure behavior for a well with a low conductivity vertical fracture, (kfbf)D less than or equal to 0.1; these cases include low kfbf fractures, long fractures or wells in relatively high permeability formations.

It appears that this type of systems exhibits two flow periods only: bilinear flow and pseudo-radial flow. It is demonstrated that for these fracture conductivities the effective wellbore radius is given by rw' = 0.28 (kfbf/k); that means that there is a maximum value of the effective wellbore radius achieved by hydraulic fracturing for a given value of (kfbf/k).

A new single line type curve is presented for analysis of pressure transient tests.

Introduction

Evaluation of hydraulic fracturing has been attained successfully through the analysis of pressure test in the last few years. These has been possible because of the introduction of new models for fractured wells such as the finite conductivity fracture and the fractured well in a layered reservoir among others.

The use of the pressure derivative has enhanced the interpretation reducing the uniqueness problem when the type curve matching procedure is applied. Pressure transient analysis allows the estimation of fracture half length xf, fracture conductivity kfbf, fracture skin sf and effective wellbore radius rw'.

It has been established that a well intersected by a fully-penetrating finite conductivity vertical fracture exhibits in general the following flow periods.

Initially, there is a fracture linear flow; after a transition flow period may or may not exhibit a bilinear flow period might develop. Eventually, in all cases, the system reaches a pseudoradial flow period.

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