Pressure Transient Analysis Of Tight Western Gas Sands - Pre- And Post- Fracturing
Authors: Kennedy J.H. , McElhiney J.E. 
Published: December 2007

In the last several years the Department of Energy, together with various industrial participants, has funded a series of massive hydraulic participants, has funded a series of massive hydraulic fracturing (MHF) experiments in the Upper Cretaceous formations of the Rocky Mountain gas provinces. The purpose of these large stimulation provinces. The purpose of these large stimulation treatments is to enhance the productivity of these low permeability reservoir systems so that commercial economics will become a reality. The initial stage of this study encompasses the pressure transient analysis of various tests run in pressure transient analysis of various tests run in several different MHF projects. Some of the preliminary results for the Mobil F31-13G well located preliminary results for the Mobil F31-13G well located in the Piceance Creek Gas Field, located in Rio Blanco County, Colorado, are reported here. These results are fraught with a variety of difficulties; these problems are discussed and recommendations for improvements in future pressure testing programs associated with MHF programs are made. programs associated with MHF programs are made

Introduction

A study to determine the effects of Massive Hydraulic Fracturing in Tight Western Gas Sands was initiated by the Department of Energy. The area of research considered in this project is the Piceance Basin of Western Colorado. The Mesaverde Piceance Basin of Western Colorado. The Mesaverde and Ft. Union formations are to be considered. The formations are low in permeability, primarily less than 0.1 md.

The DOE has supported several attempts of Massive Hydraulic Fracturing in the area and contracted for an independent analysis of the results. Three wells are to be examined in this study. The wells are:Mobil F31-13G, Piceance Creek Field, Colorado,Rio Blanco Natural Gas Co., Federal 498-4-1, Rio Blanco County, Colorado,CER's RB-MHF-3, Rio Blanco County, Colorado.

Pressure transient tests have been run on the wells for both pre- and post- fracturing. The objective is to determine the reservoir and fracture characteristics from the test data. A second part of the study, which is not reported here, is a parametric analysis. A parametric study is to be parametric analysis. A parametric study is to be run to determine the sensitivity of various reservoir and fracture characteristics on the productivity and well test design. productivity and well test design. Mobil well F31-13G was chosen as a starting point. Several buildup and deliverability tests point. Several buildup and deliverability tests are available on the well. The pressure measurements are good but the wellbore storage effects are large and rate data isn't well known. This is an on-going project and some of the interim results are reported.

Several publications in the literature present pressure analysis techniques of fractured pressure analysis techniques of fractured reservoirs. Raghaven presents a summary of the various methods for fractured flow analysis. Most of the work to date has considered infinite conductivity fractures or uniform flux vertical fractures. Recently several papers have been published on finite conductivity fractures by Cinco published on finite conductivity fractures by Cinco and Samaniego and Cinco-L., Samaniego-V., and Dominguez-A.

A numerical simulation scheme for fracture gas reservoirs was reported by Dowdle and Hyde. This radial coordinate simulator was modified to include the effect of fractures in the reservoir and a van Everdingen-Hunt type skin factor on the fracture face. The reservoir simulator has been used to analyze the data for two producing zones of the Mobil well F31-13G. The zones of interest are Zone 1 and Zone 3. The pre- and post - fracturing tests were run to determine the effect of MHF on the characteristics of the reservoir and fracture system.

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