Rheological studies and optimization of Herschel–Bulkley parameters of an environmentally friendly drilling fluid using genetic algorithm

Abstract

The Herschel–Bulkley rheological parameters of an environmentally friendly drilling fluid formulated based on an Algerianbentonite and two polymers—hydroxyethyl cellulose and polyethylene glycol—have been optimized using a genetic algorithm.The effect of hydroxyethyl cellulose, temperature, pH and sodium chloride (NaCl) on the three-parameter Herschel-Bulkleymodel was also studied. The genetic algorithm technique provided improved rheological parameter characterization compared tothe nonlinear regression, especially in the case of drilling fluids formulated with sodium chloride making it a better choice.Furthermore, the oscillatory test offered more reliable yield stress values. The rheological parameters were found to be verysensitive to different conditions. Yield stress and consistency index increased with increasing the hydroxyethyl cellulose con-centration, reaching maximum at a temperature of 65 °C and decreased with decreasing pH and also when adding sodiumchloride to the drilling fluid. The flow index changed inversely to yield stress and consistency index. The physical origins of thesechanges in rheological parameters were discussed and correlation between variation in rheological parameters and bentonitesuspension properties were concluded. Based on these results, it is recommended to use the proposed formulation of drilling fluidat high temperature and when the formation of alkaline pH is encountered due to the gelation mechanism and to select theoptimum concentration of NaCl to avoid degradation of the rheological parameters