Innovative Methods for Reservoir Fluid Composition Recovery Using Tracers in Oil-Based Mud

This study examines the impact of sample contamination with oil-based mud filtrate on the analysis of various reservoir fluids, including gas condensate and volatile oil. During the drilling process, excessive pressure in the mud column causes the oil-based mud filtrate to infiltrate the formation. This hydrocarbon-based filtrate mixes with the formation hydrocarbons, making it challenging to obtain a truly representative reservoir fluid sample, especially in open-hole wells. Depending on the reservoir type and conditions, the oil-based mud filtrate may be fully or partially miscible with the formation fluid. In oil reservoirs, the filtrate dissolves completely in the reservoir oil, meaning the captured sample contains the actual reservoir oil along with added filtrate. However, gas condensates particularly lean gas condensates are often not entirely miscible with the mud filtrate. As a result, the mass exchange between the two fluids alters the sample's composition, reducing its accuracy in representing the reservoir fluid. This research proposes two simple methods to retrieve the original composition from contaminated samples, particularly in cases where the mud filtrate is fully dissolved in the reservoir fluid (i.e., reservoir oil samples). Additionally, a tracer-based technique has been developed to determine the composition of an uncontaminated reservoir fluid sample, even in situations where the two fluids are only partially miscible. Tracers are introduced into the drilling fluid at minimal additional cost to mud preparation. The effectiveness of these techniques has been evaluated against deliberately contaminated reservoir fluid samples under controlled laboratory conditions, with results confirming the reliability and efficiency of the proposed methods.

کلیدواژه ها:

Oil-based drilling fluids ، Fluid sampling ، Tracer-based technique ، Laboratory validation