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.
The objective of this work comes from the limitations of some spacers in terms of temperature and desired rheology. A previous technology weighted spacer (henceforth referred to as Spacer B) is a low-rheology spacer and works in a limited temperature range. This gives a limitation of its use in ERD wells and other HPHT wells. Similarly, low-cost weighted spacer (henceforth referred to as Spacer C) has its limitations for use in HPHT wells. It also has a gelling problem at higher densities. To meet the need of the industry for a spacer that can be used in HPHT wells and have consistent YP over a wide range of temperature and densities, a new spacer (Spacer A) was developed (Dealy et al. 2007). This spacer gives the operator the flexibility to design it for various densities to achieve required YP. This study was initiated to validate the performance of Spacer A against Spacer B and Spacer C.
In Part I of the study, the performance of Spacer A and Spacer B was evaluated based on their individual rheology performance at high temperatures. Part II deals with the compatibility testing of Spacer A and Spacer B with various muds and brine. An extensive set of compatibility tests of Spacer A and Spacer B were done to ensure the viscosities fall in tolerable limits when the spacers are contaminated with mud and brine. Part III compares the performance of Spacer A with Spacer C at high temperature.