There are many factors to consider in the design and execution of a cement job for deepwater operations in the South China Sea. These factors include the abnormally pressured sands with high probability of shallow flows, presence of gas hydrates, low-fracture pressure formation, low bottomhole circulating temperature, and low seabed temperatures.
There have been 14 deepwater wells, offshore Sabah, Malaysia, that were successfully drilled to objective under these challenging conditions. This paper presents a few selected case histories from the project, describing the solutions-oriented approach to these problems. Also included is a discussion of the extensive laboratory tests performed to formulate the lightweight, gas-tight cement slurry at low bottomhole and seabed temperatures, and recommended practices for drilling and cementing.
Due to low-fracture-gradients associated with the deepwater environment, lightweight slurries were required to complete the cementing operation without losses. To reduce the risk of destabilizing gas hydrates, the slurries were designed to generate low heat of during their hydration and setting. Slurries were also designed with low porosity, using special additives to prevent gas migration through them during the setting process. Because of the low temperature at the seabed 1.7 °C (35 °F), special additives were required to obtain a short critical hydration period (CHP), early compressive strength development, low set-cement permeability, low fluid loss, and zero free water and sedimentation. An engineered solution was used to predict and simulate the temperatures during the cementing operation, and the simulated results were applied to improve the design.