Evaluation of clay stabilizers for a sandstone field in central Saudi Arabia

An oil field in central Saudi Arabia produces super-light crude from a sand stone reservoir. The formation contains up to 7.0 wt% authigenic clays domi nated by kaolinite and illite/montmorillonite mixed layer clays. To mitigat e sand production and improve well productivity, a frac pack stimulation tr eatment was conducted on most producing wells in this field. The treatment introduced several fluids, which might invade the formation and induce form ation 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 us ing reservoir cores under reservoir conditions. The critical salt concentra tion (defined, as the salt concentration below which there is loss of perme ability) was first determined. Several commercial clay stabilizers, cationi c polymers, were evaluated. The effects of stabilizer type, concentration a nd acids on core permeability were investigated in detail. The experimental results indicated that the critical salt concentration (KC I brine) was nearly 5 wt%. Severe loss of permeability was observed when br ines of lower salt concentrations were injected into reservoir cores. The e ffectiveness of clay stabilizers was found to be a function of chemical typ e and concentration. Some of the chemicals caused loss of injectivity at hi gher concentrations. It was found that these chemicals did not readily diss olve 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 t his 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 fi eld. Field results indicated that the chemical did not cause loss of inject ivity, and minimized formation damage due to fines migration and clay swell ing.