Changes in Pakistan crude oil properties contaminated by water-based drilling fluids with varying KCL concentrations

Drilling fluids are the most imperative element during drilling activity. Apart from their significance during drilling operations, they are also responsible for causing formation damage within reservoir through invasion. The invaded volume of drilling fluid in both flushed and transition zones not only damage the permeability of the reservoir, but can also significantly change the characteristics of the reservoir fluid through contamination. The contaminated crude oil will eventually lead to erroneous valuation of the reservoir fluid properties, which will directly impact the overall estimation of the operational cost. Understanding and examining the influence of drilling fluid contamination on reservoir fluid properties is the primarily objective of this study. During the preliminary stage, five samples of water-based drilling fluid having different concentrations of salt (i.e., KCL) ranging from 6 to 18 g were prepared. The samples were analyzed in terms of filtration and rheological properties. As the concentration of KCL increases till 12 g, an improvement in rheological properties and filtration volume was observed. Further increase in salt concentration degrades the drilling fluid. This degradation occurs because of poor performance of filtrate control material and segregation of KCL as concentration increases. Moreover, these five samples were than mixed in varying ratios of 8:2 and 6:4 (crude oil/drilling fluid) in crude oil, which was obtained from Northern region of Pakistan. Initially, the uncontaminated crude oil has the characteristics of heavy oil with high viscosity and lower API gravity. Measurement conducted on contaminated crude oil samples indicates the alteration of fluid properties with increase in viscosity and density. These variations in properties will eventually affects the flowing capabilities of the oil through the production system and will increase the overall cost of the project.