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Abstract

This paper consists of three parts. The first part presents new type curves for a well part presents new type curves for a well intercepting a vertical fracture with finite conductivity. The type curves are for a well located in a limited reservoir and producing under constant flowing pressure. The second part describes how the type pressure. The second part describes how the type curves can be used in predicting and matching reservoir performance. Description of automated history match is also included. The match procedure considers the effect of turbulent flow inside the fracture as well as the change in fracture conductivity due to change in flowing pressure (crushing of sand).

The third part of the paper presents application of the first two parts to actual field cases. The discussed procedure is applied to two gas wells in South Texas. The paper presents the following for each well:

  1. A prefracturing build-up test analysis.

  2. Fracturing treatment design.

  3. History match of production data calculating the fracture length and conductivity.

Introduction

Evaluation and design of hydraulic fractures located in a tight gas reservoir is one of the important aspects that concerns both service companies and producing oil companies. The conventional method of evaluating such a design is to run a drawdown or a build-up test after fracturing. Semi-log and type curve matching methods are then used to calculate a fracture length and conductivity. Because of the limited duration of these tests, the calculated parameters might not always be reliable. A different method is to use long-time production data. This technique is referred to as history matching. History match has a distinct advantage over the conventional methods for having much longer duration. On the other hand, it is much more difficult to perform.

The topic of history match has been generally discussed in the literature. The use of type curves for predicting reservoir performance has been also recognized. performance has been also recognized. This paper presents new type curves for a fractured well, and discusses their applications in design and history matching. The paper basically consists of three parts. The first part of the paper relates to type curves for a part of the paper relates to type curves for a well intercepting a vertical fracture with finite conductivity. The well is producing at a constant flowing pressure and is located in a limited reservoir. Constant flowing pressure at the wellbore makes these type curves most suitable for tight gas reservoirs.

In the second part, application of the type curve for designing a fracturing treatment is discussed. An example using type curves in designing fracture conductivity is reviewed.

In the last part of the paper, the type curves are used in evaluating actual field cases. Evaluation is done by using the history match technique and is achieved using a non-linear optimization technique. A published method utilizing a non-linear regression technique is used to achieve a solution with least error. it is briefly discussed in the history match portion of the paper.

Mathematical Model Describing the Type Curves
Statement of the Problem

The well is assumed to be vertically fractured in the center of a square reservoir and producing at a constant bottom hole pressure under unsteady state conditions. The formation has a constant height. The outer boundaries of the reservoir are no-flow boundaries. The fracture extends an equal distance on each side of the wellbore. The fracture is propped and has a finite capacity (W f K f). It propped and has a finite capacity (W f K f). It completely penetrates the formation in height. Other assumptions are used in developing the model.

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