Experimental study on the effects of cement contamination in a water based mud

Abstract

Drilling mud is used to ensure save and cost-effective drilling operations. In every phase of the drilling operation, contaminants are encountered which directly affect the properties of the drilling mud. The severity of drilling mud contamination depends on the type of drilling mud used, the type of contaminant and the degree of contamination. In most drilling operations, cement contamination occurs one or more times when casing strings are cemented and the plugs are drilled out. Drilling mud is discarded when cement contamination is too high such that it is practically unreasonable to treat it. It is therefore important to monitor the mud’s properties against contamination to ensure the basic functions of the mud. To perform effective monitoring of a drilling mud requires proper knowledge of the drilling mud chemistry, properties, and contaminants. This will help oil operators to apply the right control measures and treatment methods during drilling operations. This paper presents an experimental study on the effect of various concentrations of cement contamination on some physical properties of water based mud (WBM). Four mud samples were prepared of which three of them were contaminated with 10 g, 20 g and 30 g of class G cement. Rheological properties at temperatures of 25◦C, 40◦C and 60◦C as well as the pH, fluid loss and density of the mud were determined. The findings showed that the yield point and gel strength at all test temperatures increased as the concentration level of cement increased. However, the plastic viscosity decreased slightly with cement concentration of 10 g and 20 g and further increased with 30 g of cement contamination at 40◦C and 60◦C. The fluid loss, density as well as the pH of the WBM increased gradually as the concentration of cement increased. It is recommended that the effect of cement contamination in WBM at temperatures higher than 60◦C should be investigated.