Abstract

Evaluation of production data in Southwestern West Virginia had identified five Devonian shale well type categories and average reservoir properties associated with each category. Permeability-thickness product can be uniquely identified from history matching product can be uniquely identified from history matching regardless of the variability of other match parameters. Pressure buildup analyses conducted on three wells Pressure buildup analyses conducted on three wells confirms this. A simple relationship exists between the permeability-thickness product and ten-year cumulative production. History match data suggest that natural fracture property variations result in well quality variations.

Introduction

Columbia Gas is conducting a study to determine production controls presently active in a production controls presently active in a Southwestern West Virginia study area (Figure 1). This will be accomplished by determining the stratigraphic location and rate of existing gas flows and relating this information to the geological characteristics of each flow zone.

Attempts will then be made to establish a correlation between the production control features identified and actual production performance. Eight unstimulated shale wells completed open-hole provide the basis for this characterization. Analyses include that of: pre- and post-cleanout well tests; open-hole logs; flow data; and sidewall cores. The results of the characterization work then may be extended to a larger geographical area on the basis of relationships established from production data analysis.

The purpose of the production data analysis work is to describe be gas flow from Devonian shale wells. The practical outcome of this analysis is the identification of general producing categories and determination of reservoir properties unique to a given group of wells. Since production is usually the only abundant source of information available for evaluating the Devonian shale, reservoir simulators are relied upon to a great extent. This endeavor utilizes the two mathematical models, SUGAR-MD and an analytical model developed by S. A. Holditch and Associates, Inc.

This paper presents information regarding:

  1. decline curve typing using decline curve profiles and normalized matrix production data;

  2. history matching using two different mathematical models; and

  3. pressure buildup results from three shale wells.

The relationships developed here indicate that well quality and future productivity can be identified early in the life of a well. This has important implications in developing an exploration/exploitation plan targeting potential high quality shale well plan targeting potential high quality shale well drilling sites.

WELL TYPE CLASSIFICATION

Devonian shale production performance strongly suggests the presence of a dual porosity reservoir. Production decline curves usually consist of two Production decline curves usually consist of two distinct segments. Figure 2 demonstrates this behavior. The early part of the curve demonstrates relatively high initial flow rates which rapidly decline; this is characteristic of natural fracture depletion. The latter section of the curve shows a long period of low flow rate with very little decline; this indicates a matrix of very low permeability. The matrix acts as the primary source permeability. The matrix acts as the primary source of gas, whereas the natural fractures provide the means for gas to get to the wellbore.

Ninety-four individually metered gas wells were used to establish the four major and one transitional decline curve classifications in our study area. Two techniques were used in identifying (and in cross-checking) decline categories, namely, matrix gas normalization and production decline profiles.

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