More and more drilling occurs in frontier areas and particularly in deep water. In this environment, where the water depth often ranges between 1000 and 3000 m, the temperature at the seabed is extremely low, reaching 1 degC. In addition, a nonlinear temperature gradient in this water column and the sea currents further participate in and accelerate the cooling of the fluids in the wells. These low temperatures considerably slow cement hydration, which adversely affects the compressive strength development of the cement slurries.
The young, soft formations encountered in the first few thousand meters below the seafloor preclude the use of normal-density cement slurries. However, conventional low density cements take a long time to set and develop significant strength at these very low temperatures. The daily rate of the rigs able to drill these deepwater wells is fairly high. In addition, the latest generation of offshore deepwater rigs is designed to work faster and deliver wells drilled more efficiently. It is therefore important to have lightweight cement systems that set quickly and develop high strength in the short period of time compatible with the operation of these new rigs.
Often, the permeable layers below the seabed contain either free gas, when the water depth (and pressure) is reasonable, or gas hydrates at greater water depth. The lightweight cement system used in deepwater wells must therefore also control gas during its setting process at these low prevailing temperatures.
This paper will address the selection of proper deepwater cement slurry. Several case histories are also presented, where lightweight cements capable of setting quickly and managing gas flow in low temperatures have been required to economically drill and case formations with low fracture gradient in deepwater wells.
