Increased Success Rates for Squeeze-Cementing Using a Surfactant Soak -The Vital Role of Surfactant Concentration

Abstract

Abstract Historically, in the Melibur oil field in Sumatra, Indonesia, typically more than two squeeze-cement jobs are required before cement isolation is achieved. Eventhough the goal for water-zone shut-off is eventually achieved, we tie-up staff and equipment an the cost per water-shut-off is high. This circumtance challenged us to try a different squeeze cementing technique in order to achieve water-shut-off after one squeeze cementing job. We considered various different approaches, such as modifying the cement recipe, injecting water-conformance chemicals and a surfactant soak. Fluid-compatibility tests were performed, where various chemicals were added to a mixture of formation oil and water, to see which chemicals were most effective to de-emulsify the oil-water mixture. The idea was that cement would better bond with the formation water if it were separated from the formation oil. Knowing the wetting characteristics of the reservoir rock is a must before deciding to use surfactant. The chosen surfactant must be water-wet and be non-damaging to the formation. We found an anionic surfactant was best for our formation. Next came the hardest part, deciding the concentration of surfactant. In the lab, we increased the surfactant concentration gradually from 0.5% to 4% to see the effect on the cement bond. We found that if the surfactant concentration was too high, then the setting of the cement was retarded, and the additional waiting time was unacceptable for the field operation. We found that a 3 % surfactant with a 12-hour soak in the reservoir was best. An additional benefit of the surfactant was it changed the oil-wet rock into water-wet rock, and thereby mobilized oil that was trapped near the rock surface. This made it easier for cement to bond with the formation. This surfactant soak technique has been performed on seven wells to date. The first well required two squeeze-cement jobs to isolate the water, and the remaining six wells required one squeeze-cementing job. The failure in the first well was thought to be due to the incomplete mixing of the surfactant in our homemade batch mixer. After the first job, the batch mixer was modified with a more powerful hydraulic motor and a different agitator blade. This technique is considered a big success, and is now standard practice in the Melibur oil field. This project demonstrates that old problems can be solved cheaply and effectively if we turn out thinking upside down.