The Development and Successful Field Use of Viscoelastic Surfactant-based Diverting Agents for Acid Stimulation

Abstract

Abstract The success of a stimulation treatment or gravel packed completion is often dependent on the ability of the diverting agent to force the acid treatment into different portions of the reservoir. Diversion of acid treatments in the Gulf of Mexico (GOM) have been predominately accomplished by using either foam, HEC, or particulate matters to "temporarily" block off the zones and force the acid elsewhere. Recently, viscoelastic surfactant based diverting agent has been successfully used in acid stimulation in GOM. The fluid generated its viscosity through the densely packed surfactant aggregations, called vesicles. Normally, densely packed conventional surfactant vesicles require high concentration of surfactant to generate adequate viscosity. A new fluid was developed by incorporating a polyelectrolyte with the surfactant to facilitate the vesicle formation, to reduce surfactant concentration and to enhance thermal stability of the fluid. The rheological properties of the fluid can be adjusted by fluid pH, surfactant concentration, and properties of polyelectrolyte and temperature. An internal breaker package was developed to break the surfactant gel and reduce the fluid viscosity to that of water at the desired time and temperature. This system does not require contact with formation fluids, brines, or acids for clean up to provide optimum production. The Core tests were performed and the results demonstrated that there is no formation damage observed in treated core. This paper describes the fluid properties at various pH's, surfactant and polyelectrolyte concentrations, temperatures, internal breaker loading, and salt concentrations along with two successful case histories.