Revolutionizing Zone Isolation: Swellable Material Triumph in Bunyu Field, North Kalimantan, Indonesia

Abstract The Bunyu oil field in North Kalimantan, Indonesia, began production in 1952, peaking in 1959 at 10,072 barrels of oil per day (bopd). Its reservoirs contain sandstone lenses across deep, middle, and shallow zones. Challenges like pressure depletion, water coning, water breakthrough, and sand production arise due to its mature state. Economic constraints demand cost-effective solutions. Production strategy lacks a bottom-up approach, leading to perforation based on reserves rather than systematic reservoir exploitation. Consequently, zonal isolation through squeeze cementing is often necessary post-production. However, achieving satisfactory results, especially in shallow zones with loose sand, proves challenging. Historical data reveals repeated attempts before securing permanent seals, with leaks common during pressure tests. Well B-X, in production for five years, began producing from the middle to shallow zone, specifically Zone K, in 2020. After nearly two years of production, an attempt was made in 2022 to perform squeeze cementing for zonal isolation following the depletion of hydrocarbons from Zone K. However, notable losses occurred during the injectivity test phase of the operation. To mitigate these losses, conventional Lost Circulation Material (LCM) was injected into Zone K, successfully reducing the losses to a sufficient level for the cement placement. Despite this intervention, the cement failed to hold pressure during the integrity test, indicating a 20 psi pressure decrease in 30 minutes. In 2023, a workover rig returned to Well B-X due to high water production suspected to originate from Zone K. Upon tubing retrieval, a large hole was discovered in the tubing across Zone K, likely due to high water and sand production erosion. Another injectivity test revealed high losses in Zone K, highlighting the ineffectiveness of conventional LCM for shallow zones. In response to the water production issue in well B-X aggravated by losses encountered in Zone K, a strategic solution was implemented. Swellable material, consisting of a blend of super absorbent polymer and osmotic swell mechanism, was injected into Zone K in 2023, followed by a squeeze cementing operation. This comprehensive program aimed to address both the water production challenge and the losses experienced in Zone K. The integrity test results were promising, with Zone K demonstrated exceptional performance by sustaining pressure without any drop for 30 psi over 30 minutes. This outcome demonstrates the efficacy of this innovative solution, to stop water production issues and rectify losses in the targeted zone effectively.