The primary cement job is critical for a successful well completion. To achieve a successful well completion, effective and complete mud removal from the well is recommended (Ravi et al. 1992; Crook et al. 1980). Spacers and flushes are used to remove the mud from the well where cement is to be placed. As hydrocarbon resources become less accessible, operators are required to explore and produce from increasingly more difficult environments. Today, with the increasing number of HTHP wells being drilled, the design of robust yet stable spacers is becoming more critical. Various spacer fluids are available in the oil and gas industry to target effective mud removal. However, these spacers may not be suitable for HPHT wells. The performance of a spacer mainly depends on the rheology of spacer at the desired elevated temperature. In addition, a spacer should be compatible with the highly fit-for-purpose mud being used in the well. This paper compares the performance of Spacer A (advanced performance for weighted spacer) with Spacer B (previous technology weighted spacer) and Spacer C (low-cost, weighted spacer) in detail at various temperatures (80°F, 150°F, 250°F and 350°F) and their compatibility with various water-based muds (brine, clay type, and clay-free).
The new spacer is unique in that the rheology (specifically, the yield point (YP)) remains constant over a wide range of temperatures (80°F up to 350°F). Typically, the spacer YP will fluctuate as a function of temperature. The YP of the fluid plays a critical role in the displacement of mobile mud and erosion of dehydrated mud. In addition, the new spacer is designed to provide accurate and reproducible results from the laboratory to the field, which minimizes testing within the laboratory and on the rig. Lastly, the spacer can be mixed in any equipment found in the oil-field, even mix-on-the-fly applications.