Abstract In the oilfield industry, many resources have been allocated to develop lightweight slurries that will reduce the equivalent hydrostatic pressure against low-pressure formations and achieve successful zonal isolation while performing a cementing job. However, to comply with the standard recommended practices for cementing operations, it is crucial to maintain a progressive rheological and density trend from the spacer up to the tail slurry. Centralization and friction pressure play another very important role in achieving a suitable design and have to be considered during the design stage as well.
This paper describes how a lightweight spacer with 0.88 g/cm3 (7.3 lbm/gal) density was developed and its important contribution while performing a cementing job in a depleted zone.
One of the main contributions is the possibility for decreasing the hydrostatic pressure and the equivalent circulation pressure by increasing the spacer column length. By increasing the column length, additional mud can be returned to the surface, which would represent an important cost savings in cases where the mud is expensive and could be reused.
Not using nitrogen to reduce the hydrostatic pressure also contributes to savings in operational costs and facilitates the job execution and logistics. Eliminating the use of diesel in the spacer to reduce its density minimizes the possibility of having incompatibility and contamination problems with the cement slurry. The reduction of the ecological impact is also an issue to consider.
Finally, we might be able to evaluate features and benefits of this technology as well as its future applications in the industry.
Introduction The Cantarell oil field in the Gulf of Mexico is located in the Bay of Campeche. It is the largest oil field in the area with an average production of 317,975m3/d oil (2 million BOPD) from the Brecha formation. The formation is in the Paleocene and Cretaceous zones with a thickness from 150 m to 900 m (492 ft to 2,953 ft) and greater than 5-µm2 (5-darcy) permeability.
After producing for more than 25 years, this field has been depleted. Several years ago, wells were drilled without any returns (total lost circulation) using oil-based drilling fluids with densities as low as 0.88 g/cm3 (7.3 lbm/gal). These levels do not even reach the surface [1,500 m (4,921 ft)] below the surface] due to their low integrity where the formation pressure gradient is equivalent to 0.55 g/cm3 (4.6 lbm/gal) and the fracture pressure equivalent to 0.65 g/cm3 (5.4 lbm/gal). These very low pressure conditions resulted in considering the use of ultralight cement slurries with similar densities to the drilling fluid to bond the production casing during the final stage of the well construction.
The use of ultralight cement slurries has also created the necessity for the evolution of the spacers used during the cementing operations in terms of density.
The Need for an Alternative Ultralightweight Spacer In accordance with the recommended minimum criteria to ensure a good cementing job, the design of an alternative spacer represented a challenge for cementing jobs in the Cantarell field.