Sandstone acidizing using a new retarded acid system based on gemini surfactants

Sandstone acidizing treatments are conducted to remove the damage in the near-wellbore area and restore the well productivity. Clays and feldspars are abundant in sandstone formations and they have very large surface area compared to quartz and this will deplete the injected HF acid and prevent its deep penetration to remove the damage. There are several environmental and formation damage concerns with the existing retarders such as aluminum chloride, boric acid, and phosphonic acids. In this study, a newly synthesized cationic gemini surfactant was investigated as a new retarder during sandstone acidizing using HF/HCl mud acid system. The new surfactant adsorbed on clays and feldspars surfaces and prevent their reaction with the HF/HCl mud acid. This will allow for more reaction with silicate and the acid can penetrate deeper and remove the damage. Coreflooding experiments were conducted using 12-inch long Scioto sandstone cores with very high clay contents. This work also included a numerical modeling study of the mud acid reactive transport in sandstone. The calibrated model was then implemented to predict the new surfactant impacts on the mud acid penetration and permeability enhancement at field-scale. Numerical simulation was done on the core and field scales. Coreflooding experiments showed that, flushing the rock sample with a 0.5 wt% solution of the new surfactant before the acid treatment minimized the interactions between both HCl and HF with clays and feldspars. This was confirmed by the pressure drop profile during the treatment, ICP cation analysis, and HF concentration collected from the coreflooding effluent. The numerical study showed that the new surfactant could reduce the minerals' surface area exposed to the mud acid by five times. The field-scale simulations showed that the new system would result in an important increase in the acid penetration length and permeability improvement.