Effect of Calcium Carbonate on the Properties of Acid Soluble Cement Slurry

Abstract

Cementation process in oil well drilling can be challenging, causing serious well control issues. The properties of cement slurry aid the designer to know the accurate dynamic placement of the cement slurry from surface to downhole of the wellbore. It presents the stability of locally sourced CaCO3 and class G cement slurry blend, giving insight to the effective pumpability and setting time for better slurry placement. Utilization of locally source recipes serving as an alternative use to imported additives in the reduction of oilfield cementation operations is imperative, considering the cost of imported chemicals. In this paper, fine CaCO3 identified as an acid-soluble additive was used for the design and formulation of a plug cementation operation through coil tubing for zonal isolations. Four different blends of CaCO3 containing 20%, 25% 30%, 40% BWOC and 100% Class ‘G’ cement used for the experiment at a test temperature of 175degree F BHST and a slurry density of 15.8ppg to ascertain the impact of CaCO3 on the mixability, pumpability, stability on the cement slurry. The placement time and strength data of cement slurry is very crucial to meeting planned cementing schedule. From the thickening time evaluation, at 40BC an average range of 8hrs-11hrs pumpable time was deduced for all blends. However, the point of departure for 30% CaCO3 BWOC showed a better result. The result helped to provide real-time information about the initial compressive strength development in the slurry specimen and this aids in determining waiting on cement time (WOC). It indicates that the more calcium carbonate in the system, the lesser the strength which means that the presence of calcium carbonate reduces the compressive strength in an acid-soluble cement slurry compared to the neat slurry. The paper presents experimental details on the average wait on cement time and the pumpable time for acid soluble cement slurry, contributing to data gathering and proper well planning before execution and. competency in the use of the slurry designs have been established in this work.