An Area-of-Review Variance Study of the East Texas Field
Authors: Warner D.L. , Koederitz L.F. , Laudon R.C. , Dunn-Norman S. 
Published: December 2007

The East Texas oil field, discovered in 1930 and located principally in Gregg and Rusk Counties, is the largest oil field in the conterminous United States. Nearly 33,000 wells are known to have been drilled in the field.

The field has been undergoing water injection for pressure maintenance since 1938. As of today, 104 Class II salt-water disposal wells, operated by the East Texas Salt Water Disposal Company, are returning all produced water to the Woodbine producing reservoir. About 69 of the presently existing wells have not been subjected to U.S. Environmental Protection Agency Area-of-Review (AOR) requirements.

A study has been carried out of opportunities for variance from AORs for these existing wells and for new wells that will be constructed in the future. The study has been based upon a variance methodology developed at the University of Missouri-Rolla under sponsorship of the American Petroleum Institute and in coordination with the Ground Water Protection Council.

The principal technical objective of the study was to determine if reservoir pressure in the Woodbine producing reservoir is sufficiently low so that flow of salt-water from the Woodbine into the Carrizo-Wilcox ground water aquifer is precluded. The study has shown that the Woodbine reservoir is currently underpressured relative to the Carrizo-Wilcox and will remain so over the next 20 years. This information provides a logical basis for a variance for the field from performing AORs.

Introduction

The East Texas oil field is located in the extreme eastern part of Texas and comprises approximately 131,000 acres. The field is located principally in Gregg and Rusk Counties and in very limited portions of Cherokee, Smith and Upshur Counties (Fig. 1). The field was discovered in 1930 and is the largest oil field in the conterminous United States in the number of wells and volume of oil produced. An evaluation of the Texas Railroad Commission (TRRC) well location database for the five East Texas field counties shows a total of nearly 33,000 wells for the field.

Because of pressure declines in the reservoir, as will be discussed later, the field has been undergoing water injection for pressure maintenance since 19382. As of today, a total of 104 Class II salt-water disposal wells, operated by the East Texas Salt Water Disposal Company (SWDC), are returning all produced salt water to the Woodbine sand producing reservoir.

Since 1982, all new Class II injection wells constructed in Texas have had to have Underground Injection Control (UIC) permits from the TRRC. A condition of the permits for new wells is the performance of an Area of Review (AOR) analysis as required by U.S. Environmental Protection Agency (EPA) regulations.

Beginning in 1990, the University of Missouri-Rolla (UMR) conducted research to develop a methodology for variance from AOR requirements. The methodology developed at UMR was subsequently revised and adopted by the Underground Injection Practices Research Foundation of the Ground Water Protection Council. At the suggestion of various East Texas field operators, and with the agreement and encouragement of the SWDC and the TRRC, UMR proposed to the U.S. Department of Energy (DOE) a study of AOR variance opportunities for the East Texas field in order to determine if a basis could be found for relief from this regulatory requirement.

To initiate the study, a Steering Committee was formed to provide guidance and advice. At the initial meeting of the Steering Committee, which was held May 13, 1994, it was recommended that UMR study the variance method based upon the lack of sufficient petroleum reservoir pressure to cause flow into the lowermost underground source of drinking water (USDW). A 1995 report documents the results of UMR's investigation of this variance option.

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