Fit-for-Purpose, High-Density, Resilient Cement System for Ultra-HPHT Wells: Case Study in Brunei

Abstract

Cement sheath integrity under high-pressure and high-temperature (HPHT) conditions in the Maharaja Lela Jamalulalam (MLJ) field in Brunei is challenging to achieve because of the harsh downhole conditions. Pressures reach 15,000 psi [103 MPa], downhole temperatures rise to 165°C [330°F], and the narrow margin between the pore pressure and the fracture gradient makes mud removal and cement placement even more challenging. In addition, pressure and temperature cycling during production means cement selection with right properties is essential to maintain long-term wellbore integrity. The cement system must deliver cement mechanical properties that can withstand the downhole stresses over time. Mechanical failure of the cement sheath would create a path for wellbore fluid migration that could result in sustained casing pressure (SCP) or interzonal communication. This paper will discuss the challenges of cementing in the tight pore-to-fracture window in the MLJ field, and the design and placement of one of the world's heaviest (2.48SG [20.7 lb/gal]) flexible and expandable resilient cement systems. Wells in the MLJ field reach into a deep reservoir (4500 to 5000 m true vertical depth, TVD) where the pressures can reach up to 15,000 psi with bottomhole static temperatures reaching 165°C. The well is drilled using 2.18 SG [18.2 lb/gal] mud weight, and the production string is pressure tested at 15,000 psi; during the drilling and completion, the temperature variation is on the order of 60°C [108°F]. Based on the above well conditions, advanced computer-based simulations were used to determine the cement mechanical properties required to withstand the pressure and temperature changes. To achieve the required mechanical properties, special blends were prepared with engineered particles to impart flexibility and expansion for a 2.48 SG cement system. To manage the cement placement, state-of-the-art cementing design software was used to accurately simulate the bottomhole circulating temperatures and pressures during placement as well as to simulate pipe centralization; a 3D model for fluids displacement also proved valuable.