Prediction of Formation Damage, Fluid Loss and Rheological Properties of Water Based Mud with Corn Cob

The extent of damage to formation caused by water based drilling mud containing corn cob treated with sodium hydroxide to partially replace polyanionic cellulose (PAC) as a fluid loss control additive has been studied. Core samples were obtained from a well in Niger Delta for this study with a permeameter used to force the drilling mud into core samples at high pressures. Physio-chemical properties (moisture content, cellulose and lignin) of the samples were measured and the result after treatment showed reduction. The corn cob was combined with the PAC in the ratio of 25-75%, 50-50% and 75-25% in the mud. Analyzed drilling mud rheological properties such as plastic viscosity, apparent viscosity, yield point and gel strength all decreased as percentage of corn cob increased in the combination and steadily decreased as temperature increased to 200oF. Measured fluid loss and pH of the mud showed an increase in fluid loss and pH in mud sample with 100% corn cob. The extent of formation damage was determined by the differences in the initial and final permeability of the core samples. Experimental data were used to develop analytical models that can serve as effective tool to predict fluid loss, rheological properties of the drilling mud at temperature up to 200oF and percentage formation damage at 100 psi.