A Novel, Low Cost, Well Completion Technique using Steam for Formations with Unconsolidated Sands, Wilmington Field, California
Authors: Davies D.K. , Mondragon J.J. , Hara P.S. 
Published: December 2007

A novel well completion procedure is described that uses steam to stabilize unconsolidated, porous and permeable sands in the Tar Zone of Wilmington Field, California. This procedure has been used successfully in 13 vertical and 7 horizontal wells, with little or no sand production and no impairment of well productivity. Steam-induced sand stabilization is used in place of the more traditional, expensive gravel-packed, slotted-liner completions. This technology offers significantly lower drilling and completion costs, better control of fluid entry into the well bore, a low cost means of eliminating unwanted completion intervals in the future, and the flexibility of using production and injection wells interchangeably since they are drilled and completed the same way. The paper also discusses a successful sand stabilization workover using this technique to repair a damaged slotted liner.

Field tests were performed on steamflood producers and injectors. A typical well is cased, cemented and perforated (0.25 to 0.50 inch perforations) with a small number of holes approaching limited entry conditions. An empirically determined volume of approximately 750 cold water equivalent barrels of 80% steam are injected per 0.25" perforation. The theory is that the hot, alkaline water in the steam causes dissolution of formation minerals (particularly feldspars) which precipitate as natural cements on grain surfaces and bind adjacent sand grains.

Scanning electron microscope analysis of sand fill samples support this theory, and reveal that the cemented sand forms a "skin" approximately 0.5 cm thick. The skin is penetrated by large pores (wormholes) produced by grain dissolution, thus formation permeability is not impaired and could be enhanced.

Introduction

The cost to complete a vertical steam production well using conventional drilling and completion techniques for unconsolidated sand under current steamflood project economics are marginally economic. Current completion costs for a vertical production well completed in an unconsolidated sand with an underreamed hole and a gravel-packed slotted wire wrapped liner across the zone of interest is approximately $120,000.

The cost to complete the same well with cemented casing across the zone of interest by injecting steam through selected perforations with thermal insulated tubing, expansion joint, and thermal packer is approximately $30,000, a savings of approximately $90,000 per well. The same comparison for a horizontal steam production well is a savings of approximately $150,000 per well.

This novel, steam injection sand consolidation technology evolved from the completion procedure and injection operations of the first limited entry perforated steam injector 2AT-049 (Figure 1) in the Wilmington Field. The subject well was completed with 7" casing cemented to surface in tension. The well was selectively perforated with 7 perforations, 0.25" in diameter and placed on 80 % quality steam injection in November 1990. The well was drilled with 67 feet of rathole to limit the number of sand cleanouts due to sand backflow into the well when the steam source was shut down. The steam source was shut down December 1 and 2. A sinker bar was run at that time and tagged fill at 2842' (bottom perforation at 2823'). The December 1 cumulative steam injection was 5,230 CWE BBLS for the 7 perforations. Steam injection resumed December 3. A steam injection profile was run in January 1991 and fill was tagged at 2842'. A sinker bar run was made in March 1991 with no change in the depth of fill. No subsequent sand fill tags have been shallower than that depth. Hence the empirically determined volume of 750 CWE BBLS of 80 % quality steam per 0.25" perforation.

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