Abstract
When designing an acid treatment, the engineer often faces the question of what diversion method will be the most effective yet least damaging to the formation. Previous work has been published about evaluation methods, and conceptually diversion theory seems straightforward, but detailed post-job analysis and treatment optimization is often forgotten, especially when post-job production results meet or exceed expectation. Once a particular diverter is selected, the next question often is how much is required? If too small of volume is used, then treatment diversion will not be achieved. If too large of volume is used, then cleanup times and the risk of permanent damage increases.
Viscoelastic surfactants have recently become a popular additive for diversion pills, based on their polymer-free chemistry. Various formulations, including foam, have been successfully applied in acid stimulation treatments, but little post-job analysis has been published. Viscoelastic fluid properties vary over a pH range during acid spending on the formation and when foamed, determination of bottomhole properties is further complicated.
A tube viscometer and parallel core flow cells were utilized to determine the rheological properties and diversion effectiveness of various formulations of foamed viscoelastic surfactant at bottomhole conditions. An optimum formulation was determined, and this fluid was then applied and evaluated in a field application. A down-hole memory gauge was run during a coiled tubing acid treatment, and delta pressure changes were evaluated to determine the diversion effect.
