Enhancing the Compressive Strength of Saline-Contaminated Oil Well Cement Using Rice Husk Ash (RHA)
Abstract
Saline contamination from formation fluids poses a significant challenge to the compressive strength of oil well cement, compromising zonal isolation and well integrity. This study investigates the use of Rice Husk Ash (RHA), a sustainable pozzolanic additive derived from agricultural waste, to mitigate the detrimental effects of sodium chloride (NaCl) and magnesium chloride (MgCl2) on API Class-G cement. Experimental slurries were prepared at a density of 15.8 ppg and water-to-cement ratio of 0.44, with contaminants added at 1%, 3%, and 5% by weight of cement (BWOC), and RHA at 0%, 1%, 3%, and 5% BWOC. Compressive strength was measured after 24 hours using an Ultrasonic Cement Analyzer under simulated wellbore conditions (140°F, 3,000 psi). Results showed that uncontaminated control cement achieved 3,921 psi, while 5% NaCl and MgCl2 reduced strength by 43% (2,251 psi) and 54% (1,806 psi), respectively. RHA addition demonstrated dose-dependent recovery, with 5% RHA restoring strength to 3,106 psi (138% recovery against contaminated) for 5% NaCl and 2,850 psi (158% recovery) for 5% MgCl2, exceeding 80-99% of control values. ANOVA confirmed significant effects of contaminant type, concentration, and RHA dosage (p < 0.001), with stronger interactions in MgCl2 systems. The pozzolanic reaction of RHA, converting calcium hydroxide to additional calcium silicate hydrate, effectively densifies the matrix and counters salt-induced disruption. This research has shown that RHA, an agro-waste enhanced the compressive strength of cement in saline environments while promoting waste-to-wealth strategies in the petroleum industry.