Determination of Reservoir Fluid Properties from Samples Contaminated with Oil-Based Mud Filtrate

Abstract

Abstract Drilling with oil-based mud has gained world-wide application. Despite many benefits of using oil-based drilling muds, they may contaminate reservoir fluid samples, as their filtrates are completely miscible with the formation hydrocarbons. Obtaining reservoir fluid samples is expensive and accurate reservoir fluid properties are needed in reservoir development, it is desirable therefore to be able to determine the accurate composition and phase behaviour of the reservoir fluid from contaminated samples. In this study different types of real reservoir fluid samples (volatile oil and gas condensate) were deliberately contaminated with an oil-based drilling mud filtrate in the range of 1% to 20% on a volumetric basis and conventional PVT experiments were conducted on the original and contaminated samples. The results showed that the contamination may dramatically change the phase behaviour of reservoir fluids to the extent of changing a gas condensate to a volatile oil. A simple and practical method has been developed to determine the original composition of the reservoir fluid from contaminated samples. The method is general and it can be applied to different types of reservoir fluids, and highly contaminated samples. The measured PVT data of the contaminated sample is used to develop the phase behaviour model and is applied to predict the properties of the original reservoir fluid. The proposed method in most cases provides data within an acceptable accuracy.