Design and Feasibility of Creating Gas-Storage Caverns by Using Acid to Dissolve Carbonate Rock Formations

Abstract

Abstract The feasibility of creating gas-storage caverns by dissolving carbonate rock formations was examined based on process design, geologic factors, and preliminary economic analysis. The method involves drilling one or more wells, pumping acid into the formation, and then removing and treating the waste fluid. To enhance acid transport into the formation, the rock may be hydraulically fractured prior to pumping the acid. To analyze the requirements for creating storage volume, the following were examined: weight and volume of rock to be dissolved; gas storage pressure, temperature, and volume at depth; solubility of acid-rock reaction products; and acid costs. Design considerations and economic calculations indicate that the new method will be applied most advantageously to carbonate formations deeper than approximately 4000 feet, with limestone at depths between 6000 and 9000 feet preferred. In order to identify potential sites for applying the new method to creating storage volume, a large amount of data from carbonate formations was compiled for six states: Ohio, Kentucky, Indiana, West Virginia, Pennsylvania, and New York. Based on GIS analysis, large areas of West Virginia, Pennsylvania, and New York were identified as potentially suitable for developing carbonate-cavern storage. Smaller areas that may be suitable were identified in Indiana, Ohio, and Kentucky. The potential for application of this new method is very promising based on preliminary economic analysis that considered capital costs, well-design options and costs, waste treatment options, and cost comparison with other gas storage methods. Introduction Because natural gas is in high demand in many regions of the United States, there is an increasing effort focused on developing new methodologies that will make natural gas more readily available. Of particular interest are more efficient and safe means for storing large quantities of natural gas close to major pipelines or high usage areas. The primary focus of our investigation is to evaluate the feasibility of creating underground natural gas storage caverns in optimal locations by dissolving carbonate rock formations using acid. The analysis includes compilation of a large amount of data from carbonate formations in six states (Indiana, Ohio, Kentucky, West Virginia, Pennsylvania, and New York), which were selected based on location near major natural-gas markets and pipelines. The basic concept that we propose for creating carbonate-cavern storage is to drill to depth, fracture the carbonate rock layer if needed, and then produce a cavern using an aqueous acid to dissolve the carbonate rock. Following waste-fluid removal, the resulting subsurface cavity can be used to store natural gas. Abundant carbonate rock formations worldwide make the method attractive to both industry and the consumer, especially when the facility is to be located near large gas markets where current gas storage capacity is insufficient to meet demand. An additional benefit of carbonate-cavern storage is its suitability for developing storage capacity of specific volume near industrial facilities or power-generating plants. The first phase of our investigation has focused on developing guidelines and a cost estimate for creating gas storage caverns in carbonate rock formations that have negligible innate storage capacity (i.e., low permeability and/or porosity). There are two primary factors that determine the viability of creating an underground natural gas storage reservoir by acid dissolution of carbonate rock: the cost associated with dissolving large quantities of limestone with aqueous acids (dissolution economics) and the existence of carbonate rock formations at the appropriate location and depth (geology).