Contamination of Deepwater Well Cementations by Synthetic-Based Drilling Fluids

Abstract Synthetic based mud (SBM) contamination of portland cement slurries negatively affects the integrity of cementations in oil and gas wells, particularly drilled in deepwater environments. Few systematic studies to assess the effects of SBM contamination on portland cements have been reported in the literature, despite the industry understanding that such detrimental contamination occurs. In addition, solutions to reduce or eliminate the effects of SBM contamination of slurries have not been developed. A multi-phase project has been initiated to study the effects of SBM contamination on slurries, particularly those employed in deepwater wells (where long displacements, restricted circulation rates in tight annular clearances etc. can exacerbate the impact of mud contamination), and to assess which chemical interactions are causing the unfavorable behavior. The first phase of the project was to quantify the effects of contamination on typical portland slurries and to explore formulation changes that would make such slurries more tolerant to contamination. The control in the study was Class H portland cement, which has been the long-standing "workhorse" of the oil and gas industry for primary cementations. Two class H cements and other API cement types were investigated in the work. Alternative cements were also contaminated with the SBM for comparison with the Portland slurries. Results from the first phase of our work clarify the detailed contamination behavior of portland cements, showing the susceptibility of portland slurries to such contaminations. Results for alternative cementing formulations indicate distinctly lower sensitivity to SBM contamination. These results then provide a first set of guidelines on how to minimize and possibly avoid SBM cement contamination, which is expected to greatly help guarantee primary cementing success and proper zonal isolation in deepwater wells.