Model Study of Foam as a Sealant for Leaks in Gas Storage Reservoirs

Abstract

Abstract Previous studies have shown that foam, because of its unique structure, reduces gas flow in porous media. This blocking action of foam appears to be especially suitable for sealing leaks in underground gas storage reservoirs. Such reservoirs often have permeable areas in the overlying caprock that allow permeable areas in the overlying caprock that allow vertical migration of gas from the storage zone to the upper formations. The escaped gas represents both a safety hazard and an economic loss. Our objectives in this study were to evaluate the effectiveness of foam in preventing the escape of gas from a leaky gas storage reservoir and to find the foaming agents that were most suitable for this purpose. We simulated the behavior of a leaky gas reservoir with a sandstone model and found that foam was 99-percent effective in reducing leakage of gas through the model. The amount of foaming agent required to seal a leak depends on the adsorption-desorption properties of the agent. After testing many foaming agents, we concluded that best results are obtained with certain modified anionic esters of relatively low molecular weight. Less than 0.3 lb of such agents is required per barrel of pore space in Berea sandstone. This study indicates that foam generation should be an effective and economical method for reducing or stopping gas leakage from an underground storage reservoir. Introduction The practicality of underground gas storage is greatly dependent upon the confinement that the caprock provides for the formation to be used as a storage reservoir. In spite of numerous precautions, several gas storage projects are plagued by vertical migration of gas from the intended storage zone to upper formations. Such gas leaks pose a safety hazard and represent an economic loss. If leakage is very high, the storage operation may be uneconomical. In at least one cases the leak problem is minimized by periodically collecting the escaped gas from the upper formation and reinjecting it into the storage reservoir. While such a solution is feasible, it is economically unattractive because the leak limits pressures and gas injection rates. Furthermore, energy must be expended in order to circulate the escaped gas. Recent studies have shown that foam, because of its unique structure, reduces gas flow in porous media. This blocking action of foam appears to be uniquely suitable for sealing leaks in underground gas storage reservoirs. Our objectives in this study were to determine the effectiveness of foam in reducing gas flow in a model of a "leaky" gas storage reservoir and to find foaming agents most suitable for this purpose. APPARATUS AND PROCEDURE PREPARATION OF THE MODEL PREPARATION OF THE MODELA laboratory model representing an estimated area of gas leakage in an Illinois gas storage reservoir was constructed of 24-in. × 6-in. × 1-in. Berea sandstone (See Fig. 1). The model was coated with Hysol plastic. The model represented an area of the reservoir approximately 600 ft wide, 2,400 ft long and 100 ft thick. The section contained about 2,000,000 bbl of pore space. The major portion of the reservoir is upstream of the inlet to this estimated area of leakage. The model, then, was geometrically scaled to this area of leakage in the reservoir. Distribution channels were installed on both ends of the model to permit linear gas flow through its entire width and thickness. Three injection wells were drilled into the model about one-third the distance from the inlet to the outlet. SPEJ P. 9