Evaluation of Clay Stabilizers for a Sandstone Field in Central Saudi Arabia

Abstract

Summary An oil field in central Saudi Arabia produces super-light crude from a sandstone reservoir. The formation contains up to 7.0 wt% authigenic clays dominated by kaolinite and illite/montmorillonite mixed layer clays. To mitigate sand production and improve well productivity, a frac pack stimulation treatment was conducted on most producing wells in this field. The treatment introduced several fluids, which might invade the formation and induce formation damage. An experimental study was conducted to determine potential formation damage due to fines migration and clay swelling, and to design an effective clay stabilizer treatment. The work included performing coreflood experiments using reservoir cores under reservoir conditions. The critical salt concentration (defined, as the salt concentration below which there is loss of permeability) was first determined. Several commercial clay stabilizers, cationic polymers, were evaluated. The effects of stabilizer type, concentration and acids on core permeability were investigated in detail. The experimental results indicated that the critical salt concentration (KCl brine) was nearly 5 wt%. Severe loss of permeability was observed when brines of lower salt concentrations were injected into reservoir cores. The effectiveness of clay stabilizers was found to be a function of chemical type and concentration. Some ofthe chemicals caused loss of injectivity at higher concentrations. It was found that these chemicals did not readily dissolve in water and formed fish eyes. When these chemicals were injected into reservoir cores, they formed an external filter cake, which caused loss of permeability. Good mixing of the stabilizer and proper filtration solved this problem. Hydrochloric acid at 15 wt% did improve the performance of at least one of the clay stabilizers examined. Based on lab testing, a cost effective clay stabilizer was tested in the field. Field results indicated that the chemical did not cause loss of injectivity, and minimized formation damage due to fines migration and clay swelling.