The paper was presented at the SPE/DOE Unconventional Gas Recovery Symposium of the Society of Petroleum Engineers held in Pittsburgh, PA, May 16–18, 1982. The material is subject to correction by the author. Permission to copy is restricted to an abstract of not more than 300 words. Write: 6200 N. Central Expwy., Dallas, TX 75206.

Abstract

A systematic approach is presented for generating transient inflow performance relationship curves for finite conductivity vertically performance relationship curves for finite conductivity vertically fractured wells. A semi-analytical model was developed to simulate dimensionless wellbore pressure drop and dimensionless pressure loss through the fracture vs. dimensionless time at constant-rate of production for wells intercepted by a finite-conductivity vertical fracture. Flowing bottom hole pressure can be predicted at any time period using these dimensionless variables. System average pressure at any stage of production can be obtained through material balance calculations. production can be obtained through material balance calculations. A straight line reference curve was observed at all times provided that the real gas pseudo-pressure function is used to plot m (p wf(t))/m(pR (t)) vs. qg (t)/ q gmax (t). The advantage of normalizing the dimensionless variable in terms of pseudo-pressure function is that only one straight line relationship is obtained throughout the entire production life of the reservoir. This provides a more simple means for performance prediction purposes. prediction purposes. The major contribution of this paper is the provision of a valuable tool to study the sensitivity of fracture design parameters on ultimate well performance. The economic benefits of this approach can be substantial.

Introduction

Hydraulic fracturing has been recognized to be an effective means for improving well productivity from low permeability reservoirs. During the past decade, a large amount of energy and effort has been given to the past decade, a large amount of energy and effort has been given to the determination of transient pressure behavior of the well intercepted by a vertical fracture. As a result, three basic solutions along with analysis method have been presented. They are uniform-flux, infinite-conductivity and finite-conductivity solution for vertical fractures. Type-curve matching has been proposed as an interpretation technique to determine reservoir properties and fracture characteristics from pressure transient test data. The contributions of these works have provided the practicing engineer with a better understanding of the fractured reservoir performance. performance. In 1968, Vogel presented a correlation to generate inflow performance relationships (IPR) curves for solution-gas drive wells based on the assumption of steady-state Darcy's law. The application of IPR curves in the analysis of total production systems are well recognized. Recently exploitation of low-permeability or tight gas reservoirs has required more advanced well stimulation techniques, such as massive hydraulic fracturing (MHF). Unfortunately, the transient IPR curves for wells intercepted by a finite-conductivity vertical fracture has not been investigated until now. It should be realized that pseudo-steady state pressure behavior for a tight gas reservoir is rarely seen in the early production life of the wells. Therefore, a systematic approach for generating transient IPR curves is one important objective of this work. Several questions have been asked quite often among production engineers. How can a frac job be designed for tight gas wells? what is the optimal fracture half length? What are the tubing and surface facility constraints? Can production rate vs. fracture half length be predicted before the fracturing operations? To answer the above questions, we should look at the total system performance, i.e.; both reservoir and tubing capacity performance. The model developed in this work will allow production engineers to make a judgement using production rate vs. fracture production engineers to make a judgement using production rate vs. fracture half length relationship as a criterion in designing a fracture job.

The objectives of this work include:

  1. The utilization of type curves to predict transient reservoir performance (IPR curves) under different fracture characteristics.

  2. The sensitivity of tubing capacity performance under different conditions.

  3. Combining tubing capacity performance with reservoir performance to predict production rate vs. fracture half length relationships.

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