Techniques for Treating and Completing Water Injection Wells in California
Authors: Wade James E. 
Published: December 2007

WADE, JAMES E., MEMBER AIME, CITY OF LONG BEACH, LONG BEACH, CALIF.

Various techniques for completion, stimulation and profile improvement of water injection wells in unconsolidated sands have been field tested in the Wilmington field, Long Beach, Calif., since the start of waterflooding in 1953. The major problems confronting the operators are control of sand entry, maintenance of water injection rates and control of water advance into individual sands. Several methods of completing water injection wells include jet-perforated completions and pre-packed and floatpacked gravel liners. The most effective method of controlling sand entry is the float-packed gravel liner. Many methods tested for improving injectivity in water injection wells include acidizing, chemical washes, high rate pressure injection, back flow (drillstem tester), shock treatment with explosives and steam injection. The most effective methods of improving injectivity are high rate pressure injection and back flow (drillstem tester) and the notch and fracturing profiles in injection wells include selective acidizing, high rate pressure with temporary blocking agents, selective back flow (drillstem tester) and the notch and fracturing method. The most effective methods of profile improvement in water injection wells are selective back flow (drillstem tester) and selective acidizing.

Introduction

The Wilmington oil field, located in Long Beach, Calif., has been under active waterflood since 1953. At the present time, approximately 700,000 BWPD are being injected into 312 water injection wells. Cumulative injection to date amounts to more than 1,300,000,000 bbl. Most of the injection has taken place in the Pliocene and Upper Miocene sands of the Tar, Ranger, Upper Terminal and Lower Terminal zones. These zones consist of unconsolidated sands interbedded with shales and silt stones. The major problems encountered to date are control of sand entry, maintenance of water injection rates and control of water advance in individual sands. From 1953 to the present, many different techniques of completion, treatment and profile improvement have been used. This article presents a description of the techniques which have been used and a summary of the results achieved by each method. A total of 201 water injection wells are covered. Of this number, 76 are aquifer injectors and 125 are in-zone, pattern or line-drive injectors.

Completion Methods

In general, aquifer injectors were drilled as new wells whereas the in-zone injectors are predominantly converted producers or idle wells redrilled or recompleted. Originally, most of the new and redrilled wells were completed by selectively jet perforating. This method afforded a high degree of selectivity but resulted in severe sand problems. Current practice is to complete all new and redrilled wells with sand control liners. Water was injected originally down the casing of many wells. Excessive corrosion was encountered in subsequent casing surveys. Current practice is to inject water through tubing landed on a packer set at the top of the zone and to treat the water in the tubing-casing annulus with corrosion inhibitors.

Selective Completion by Jet Perforating

New and redrilled water injection wells were originally completed by selectively jet perforating. Standard practice was to set 9 5/8-in. casing at the top of the zone and establish a water shut-off on the 9 5/8-in. shoe. After drilling to total depth, run 6 5/8-in. liner equipped with 9 5/8 - X 6 5/8-in. top adapter, cement liner and lap, selectively jet perforate and pressure test liner lap and blanks (Fig. 1). Of the 94 wells completed in this manner, a total of 53 had a history of severe sand problems. As pressures increased around the injectors, particularly the aquifer injectors, temporary interruptions of injection plant service resulted in backflow bringing large amounts of sand into the wellbore. Serious problems were encountered in controlling sand entry during repair jobs and sand fill was often found when wells were put back on injection after remedial work. Sand problems are basically caused by the unconsolidated nature of the oil sands, but appear to be aggravated by the tendency of jet-perforated holes to become enlarged by abrasion or corrosion. Photographs of jet perforations taken in a water injection well by special camera equipment showed hole enlargement and casing fractures. Pieces of liner recovered from water injection wells also showed hole enlargement and fracturing. Two methods have been used effectively to combat sand problems in jet-perforated wells. One method is to sand pack the perforations and the other is to backflow the well by drillstem testing.

JPT

P. 49ˆ