Abstract

This work presents the basic pressure behavior differences between a finite condutivity fracture and different types of damaged fractures.

Two kinds of fracture damage conditions are studied:

  • a damaged zone around the fracture, and

  • a damaged zone within the fracture in the vicinity of the wellbore.

The first case is caused by the fracturing fluid loss in the formation and the last case is originated by crushing, embedding or loss of propant within the fracture in the vicinity of the wellbore.

This paper emphasizes that although finite fracture conductivity and fracture damage condition are both flow restrictions, their effects on transient pressure behavior are quite different at early time.

Type curves and both linear flow and bilinear flow graphs can be used to identify different cases when applied properly.

Introduction

Evaluation of hydraulic fracturing through transient pressure analysis has become a common practice today. Initially, the main objective of the application of pressure analysis in fractured wells was to pressure analysis in fractured wells was to estimate the formation flow parameters and fracture extension. These techniques considered an infinity conductivity vertical fracture and involved a trial and error procedure unless prefac information was procedure unless prefac information was available. To avoid these limitations Gringarten et al presented the type curve analysis method which allows the identification of different flow regimes and the estimation of both formation permeability and fracture half length.

Recently, the analysis of pressure data for fractured wells has been directed towards the determination of both flow and geometric characteristics of a fracture This has been possible because of the development of new solutions which consider a well intercepted by a finite conductivity vertical fracture.

Frequently, it is observed that the pressure behavior of a fractured well does pressure behavior of a fractured well does not match the infinite conductivity vertical fracture solution; instead these cases exhibit an extra pressure drop caused by a flow restriction somewhere in the system. Several models have been proposed:

  • A damaged zone around the fracture (fluid loss damage) and

  • a damaged region within the fracture in the vicinity of the wellbore (choked fracture); both cases consider an infinite conductivity vertical fracture and are referred as damaged fractures.

The purpose of this work is to show and emphasize that although finite fracture conductivity and fracture damage conditions are both flow restrictions their pressure transient behavior are quite different at early time.

While the finite conductivity case exhibit the bilinear flow behavior, the fracture damage case is characaterized by an extra pressure drop caused by the damaged zone. pressure drop caused by the damaged zone. These differences become evident when pressure data are plotted on a log-log graph. pressure data are plotted on a log-log graph. PRESSURE BEHAVIOR OF FRACTURED WELLS PRESSURE BEHAVIOR OF FRACTURED WELLS For the better application of the transient data analysis techniques, it is necessary to understand the basic flow equations that describe the flow towards hydraulically fractured wells.

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