Converting Wells in a Mature West Texas Field for C02 Injection
Authors: Power M.T. , Leicht M.A. , Barnett K.L. 
Published: December 2007

SPE Members

This paper deals with the planning, special equipment considerations and operations necessary to convert 165 water injection wells to C02 injectors that will function through at least the end of the century. The paper will be divided into two parts:the planning/engineering aspects (reviewing wellhead, packer, and tubular selection),procedural operation highlights (fishing, open hole clean out, casing evaluation and repair, stimulation, liner running practices, wellhead replacement, packer setting, and the reworking of tubulars).

A case history approach has been used to analyze the success or failure of the various methods and techniques employed in this project. All 165 wells were converted as of project. All 165 wells were converted as of March 29, 1989.

Introduction

Chevron U.S.A.'s North Ward Estes (NWE) Field is an 18 mile × 4 mile anticlinorium located in Ward and Winkler Counties, Texas. The field is approximately 60 miles southwest of Midland, Texas and geologically resides on the western flank of the Central Basin Platform.

The Yates is the dominant producing formation. It is composed of up to nine major reservoirs. The individual reservoirs are very fine grained sandstones to siltstones separated by very dense dolomite beds. The average depth of the Yates is 2800 feet.

The NWE Field was discovered in 1929 and has yielded more than 330 million barrels of oil (30% of OOIP) to date. Current production averages 2849 BOPD in the project area.

Many of the older areas of the NWE Field began approaching their economic limit in 1954. A pilot waterflood was initiated on the Hutchings Stock Association lease in late 1954. Expansion to cover the entire field was begun in mid-1955 and by 1965 approximately 26,000 acres were under waterflood.

Since 1975, a number of tertiary pilot projects have been conducted in the NWE Field. projects have been conducted in the NWE Field. These include in-situ combustion, caustic flooding and polymer injection profile modification.

In 1985 an economic evaluation of the project area was made to investigate the current viability of a C02 flood. Based on the positive results of the C02 flood investigation, a task force was established to develop the procedures for converting the wells to C02 injection. The task force was led by a project manager. Reporting directly to the project manager were a petroleum engineering group, a facilities engineering group, a project accountant and a field operations group. Assigned to work with the task force but reporting to their respective functional managers were a drilling superintendent, drilling engineer, four drilling representatives and two geologists.

The project incorporated six (6) sections of the field (See Figure 1). The project will use existing waterflood injection and production wells which are on 10 acre spacing. The average age of the wells is about 35 years with some wells older than 55 years. Ninety-six (96) or 58% of the 165 injection wells are completed in open hole. All of these wells have at least one liner, with many having two or more.

PROCEDURAL OPERATIONS PROCEDURAL OPERATIONS The objective of the conversion work was to prepare 165 wells for C02 injection. prepare 165 wells for C02 injection. P. 821