Gas and water production from CBM wells in Southwest Virginia has led to problematic deposition of mineral scales. Calcium carbonate essentially cements the production casing and tubing together, making well repairs time-consuming, difficult, and costly. In some areas, work-over operations to remove the mineral scale deposition exceed $165,000 and several weeks per well. This paper will describe a novel technology that applies acid via foamed liquid to free the tubing at a fraction of the time and cost compared with traditional means.
The applications described in this paper have been in the Southwest Virginia area. Twelve unproductive CBM wells were treated with a foamed acid that successfully, economically and quickly helped free stuck tubing. The technology uses nitrogen gas to help generate stable, self-supporting foam from a liquid acid and foamer additive. The application is made to the annulus from a truck-mounted, purpose-built skid that contains the chemical, nitrogen, pump, and foam generation equipment. Pumping foamed acid results in coverage of a larger area of the annulus compared with pumping liquid acid.
A foamed acid treatment on day one, followed by a water dump on day two, has lead to the successful pulling of stuck tubing. In addition to freeing the tubing, treated wells have provided the operator with increased gas production compared to traditional remediation methods. When treated regularly (treatment intervals range between 60-180 days), the wells maintain a steady rate of gas production.
The primary benefit of a foamed chemical application is the nearly universal coverage of the annular space. Other benefits are the elimination of the need for surface treatment equipment, low volumes of chemical required, ease of monitoring, and the ease and safety of application. This novel technology brings an economic and technologically superior solution to the problem of scale management.