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

Abstract

Abstract An oil field in central Saudi Arabia produces super-light crude from a sandstone reservoir. The formation contains up to 2 wt. percent authigenic clays dominated by kaolinite and illite/montmorillonite mixed layer clays. To improve well productivity, a well stimulation treatment has been conducted on the producing wells in this field. The treatment introduces 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 design an effective clay stabilizer treatment. The work included performing coreflood experiments using reservoir cores at reservoir conditions (180 F and overburden pressure of 1500 psi). 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 concentration (0 to 2 vol. percent.), soaking time, and acids (15 wt. percent HCl) on core permeability were investigated in detail. The experimental results indicated that the critical salt concentration (KCl brine) was nearly 5 wt. percent. Severe loss of permeability was observed when brines of lower salt concentrations were injected into reservoir cores. The effectiveness of clay stabilizer was found to be a function of chemical type and concentration. Some of the chemicals tested were not effective at concentrations less than 1.5 vol. percent. Others were effective clay stabilizers, but caused loss of injectivity at higher concentrations (2 vol. percent). After conducting a thorough investigation, 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. This problem was solved by good mixing of the stabilizer and proper filtration. Hydrochloric acid did improve the performance of at least of the clay stabilizers examined. Based on lab testing, a cost effective clay stabilizer was tested in the field at a concentration of 2 vol. percent. Field results indicated that the chemical did not cause loss of injectivity, and minimized formation damage due to fines migration and clay swelling. P. 613