Improving Cementing Efficiency by Optimizing the Spacer Train: Case Histories

Abstract After a time-consuming cement squeeze to improve zonal isolation in a southern Nigeria well, engineers returned to the laboratory for a means to ensure primary cementing performance without costly remedial operations. Spacers have proven to be indispensable in achieving effective zonal isolation and annular slurry placement in primary and remedial cementing operations. Therefore, the engineering target was an optimized spacer train that could more effectively clean the wellbore and prevent contamination of cement slurries during displacement of wellbore fluids. Laboratory testing led to a new spacer design that has effectively eliminated the need for remedial cementing in the area. The cement bond log for the well that required a cement squeeze showed good zonal isolation in some areas but poor bond in others, which indicated the conventional spacer train, was inadequately cleaning the wellbore. Laboratory testing confirmed that the conventional spacer system would remove some of the client's preferred drilling mud; however, a new water-based microemulsion spacer system removed substantially more mud based on tests conducted in the lab. As a result, the new high-performance, water-based microemulsion spacer was used in subsequent wells and has consistently resulted in good cement bond logs without remedial operations. This paper describes the engineering design, application, and operational success of this high-performance, water-based micro-emulsion spacer system that has replaced a conventional spacer in an operator field in the southern region of Nigeria, West Africa. With detailed case histories of wells treated using conventional and new spacer systems, the paper highlights engineering challenges, laboratory testing, operational procedures for field deployment, and cement bond analyses carried out after slurry placement, demonstrating the spacer system to be consistently reliable in ensuring efficient wellbore cleaning and zonal isolation. The case history wells were the first in Africa to benefit from the new spacer, which has effectively eliminated expensive and time-consuming remedial cementing operations in the area.