Multiple Zone Waterflooding In North Texas
Authors: Moyer J.D. 
Published: December 2007

Multiple zone water flooding in North Texas has resulted in reduced costs and increased recoveries through improved economics. Multiple completions of water injection wells has materially reduced development costs. Further cost savings have been realized through slimhole and tubingless completions. Operating cost savings result from reduced overhead, shorter operating time interval and concurrent use of personnel and equipment.

An actual cost survey of 79 water injection wells shows development cost savings of [1] multiple over single completions and [2] slimhole and tubingless over 4–1/2 in. casing completions. The cost survey also indicates substantial savings resulting from volume purchases and multi-job contracting by optimum scheduling.

Injection well designs for various concentric and parallel completions are discussed and illustrated. Maximum benefits can be achieved by utilizing the minimum size tubular goods that will handle the required injection rates.

The application of multiple completions to waterflood producers has not been successful. Individual zone producing rates require frequent adjustment to maintain proper pump-off. Multiple completion downhole pumping equipment is neither mechanically nor economically adaptable to multizone waterflood operations. Commingling in the wellbore and maintaining a low working fluid level would seem to be more desirable where individual producers cannot be economically justified.

MULTI-ZONE OPERATIONS

Simultaneous multi-zone water flooding results in substantial savings through the common use of the following items:

water supply facility, water treating and injection equipment, water distribution system, electrical distribution system, well test equipment, oil treating and tank battery facility and operating and supervisory personnel.

Cities Service began multi-zone water flooding in North Texas in 1957. Currently, this company is operating three one-zone, ten two-zone and four three-zone waterflood projects in the area. Several additional projects are in various stages of development at the present time.

Multiple completions have played an important part in reducing development and operating cost and have thereby increased recoverable oil on these North Texas projects. Operating cost savings result from reduced overhead, shorter operating time interval, and concurrent use of equipment. The line graph in Fig. 1 illustrates some of the advantages of multiple zone water flooding.

Within the past few years, slim-hole and tubingless completions have become recognized and adopted by many operators as a means of reducing investment costs. More and more tools for working inside reduced diameters have been made available for the more popular 2–7/8 in. casing size. However, tools for use in 2–3/8 in. casing are still quite limited. The smaller tubing offers greater opportunity for savings as these tools become available.

With the inception of slim-hole and tubingless completion techniques, Cities Service has tried several dual injection completion designs including the following:

A. Concentric completions: 2–3/8 in. casing × 1 in. tubing 2–7/8 in. casing × 1 in. tubing 4–1/2 in. [or larger] casing × 2 in. tubing B. Parallel completions: 2–3/8 in. casing × 2–3/8 in. casing 2–7/8 in. casing × 2–3/8 in. casing

With the inauguration of three zone water flooding, the basic dual installation designs were modified to accommodate a third entryway for injection. Triple completions to date include the following:

Concentric completions: 4 in. casing × 2 in. tubing × 1 in. tubing