Acid-Soluble Plugs—Pressure-Tight Solution for a Preperforated Liner

Abstract

Summary This paper covers the development, laboratory testing, and field testing of acid-soluble-plug (ASP) technology as a viable completion alternative to wireline- or tubing-conveyed perforating. The ASPs are installed in a preperforated reservoir liner and dissolve when soaked in acid, allowing access to the reservoir. This allows the technology to be easily applied in reservoirs in which matrix acid jobs or acid-fracturing techniques are used. The ASP technology was developed to reduce risk and cost associated with wireline- and tubing-conveyed perforating. ASPs were designed, manufactured, and field tested in both 5-in. and 7.625-in. reservoir liner sizes for wells in the Ekofisk field. The combination of laboratory testing and large-scale field testing influenced the design of the ASPs as well as the additives used in the acid systems used to dissolve them. From concept to initial field implementation, the process of ASP-engineering development took more than 2 years. The concept was in the beginning field-tested in deviated injectors, with ASPs installed in the deepest section of the reservoir liner. The field tests proved the ASP concept before depending on the technology in a horizontal producer with an uncemented, tubing-in-liner completion solution. The field tests showed that acid soaking dissolved the ASPs in the downhole environment and allowed efficient acid stimulation of the reservoir. It also reduced the number of wireline runs necessary to complete the well. When field tested in a tubing-in-liner completion application, installation of the ASPs in the reservoir liner eliminated tubing-conveyed-perforating runs. The reservoir liner was uncemented with mechanical openhole packers for zonal isolation. The ASPs provided a pressure-tight reservoir liner to set the packers against and eliminated fluid loss during the running of the inner completion string. Optimization of this technology is an ongoing process. The plug design itself continues to evolve as well as the operational steps to minimize the soaking time necessary to dissolve the plugs and to gain access to the reservoir.