A pozzolanic supplementary material to reinforce class G cement used for drilling and completion operations

There have been many studies to improve cement integrity under different pressure and temperature conditions where cement degradation is initiated by the mechanical and chemical interactions. Several approaches were presented so far to resolve this issue, many of which are either expensive or inefficient under certain circumstances. In this paper, attempts are made to show the application of Palm Oil Fuel Ash (POFA) as a cheap but efficient supplementary cementing material (SCM) for drilling and completions practices. A series of experiments were conducted to evaluate the changes in the density, free fluid, rheology, weight on cement, compressive strength, matrix structure and composition of the cement modified by POFA. The results obtained indicated that POFA has a hydrophilic surface and can retard pozzolanic reactions. It was appeared that POFA does not significantly change the rheology but may reduce the plastic viscosity. After 24 h and 9 months of curing, 5 wt% POFA based cement appeared to have the highest compressive strength with a very consolidated matrix as observed through XRD, TGA and SEM tests. It was also revealed that nanosilica (NS) may significantly increase the plastic viscosity of the cement while POFA may give a higher strength to the cement in a long curing process. It was then concluded that POFA can be a very good choice to improve the mechanical strength and the matrix structure of the cement under different drilling conditions.