Influx-Free Barrier for Oman Salt High-Pressure Water Zones

Abstract A unique case of salt cementing occurs in the subsalt wells in the south of Oman, which contains pressurized water-bearing zones across salt beds. To achieve zonal isolation, the cement must overcome the influx of water during the cement hydration period, create strong bonding with the salt formation to prevent the flow of formation fluids following placement, and be able to address the stresses of salt creep to avoid loss of isolation. A three-step approach was developed to address each of the challenges during the cementing of a 7-in. liner. First, a detailed salt cementing study was performed to determine the sensitivity of the slurry design to contamination from the salt formation. Second, using a stress simulation, a fit-for-purpose flexible and expandable slurry design was proposed to overcome wellbore stresses. Third, a novel laboratory testing procedure was developed to confirm the shear bonding of the cement slurry to the halite salt formation. In the event that the 8.5-in. openhole section across the salt formation encounters high-pressure water zones, mud weight can be increased to 18.5 lbm/gal to prevent influx. Therefore, a high-density cement slurry is required to maintain overbalance during the cementation of the 7-in. liner. The effect of contamination was determined in the laboratory by comparing various concentrations of formation salt and the optimal design using potassium chloride (KCl) in the base fluid. Using the outcome of proprietary stress simulations, the slurry was optimized to have a low Young's modulus and expanding properties to prevent any failure of the cement sheath integrity and migration of formation fluids resulting from a micro annulus. To confirm bonding between the slurry and the salt formation, salt cores were used in the laboratory to confirm shear bonding between the slurry and the formation. The final slurry design was optimized in the laboratory to the specific job conditions in terms of cement transition time and setting time. Cement placement and displacement procedures were adjusted to avoid large pressure changes in the wellbore that could potentially result in the debonding of the cement from the casing. A fit-for-purpose high-density, flexible cement slurry was developed to overcome the challenges encountered while drilling the salt formation. The slurry has been used on seven 7-in. liner jobs since 2023. Since the implementation of the new slurry design, all of the wells have achieved zonal isolation across the salt sections and have isolated the high-pressure water zones, enabling the operator to drill the low-pressure reservoir interval below the salt formation without the need for remediation, saving time and lowering costs.