Clay Stabilization Improves Sand Control

TAGUE, JAMES, Chevron Corp.

Recently, Chevron initiated a series of well treatments designed to improve sand control in the Coalinga field. The need for improved sand control was driven by the high frequency of pump failures, especially after remedial operations. Prior to these well treatments, most sand control efforts were focused on improving pump design and the continual replacement of old or worn-out slotted liners (re-drills). In a desire to improve overall returns and to reduce operating expenses, a study was launched to determine the primary causes of sand entry and to improve overall sand control.

The study initially gathered and analyzed data on the formation including sieve analysis, mineralogical analysis, and SEM microphotographs. Mineralogical analysis and SEM photographs obtained from core samples showed the grains to be weakly cemented by a combination of smectite and illite clays. Based on this data, a hypothesis was developed stating that wellbore sand entry was preceded by the release of the cementing clays, and thus by corollary, sand control could be improved by preventing the migration and release of the binding clays. To test this hypothesis, multiple wells were treated with a clay stabilizer designed to strengthen the chemical bond of the clays. To date 17 wells have been treated for sand control, with 14 qualified successes. Based on these results, a standard treatment procedure has been designed, and candidate selection criteria developed. Overall, clay stabilization appears to be a quick and inexpensive method of improving sand control, especially when combined with more traditional methods.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California