Effect of Oil-Based Drilling Fluid Contamination on Gas Condensates Fluid Properties. Case Study of a Deepwater Reservoir in Niger Delta, Nigeria

Abstract Fluid characterization is a key input into reservoir and field development studies and effective wells and reservoir management. Thus, the importance of acquiring representative reservoir fluid samples cannot be over emphasized. Fluid samples acquired from the reservoir may be contaminated by drilling fluid. However, with advancements in reservoir fluid analysis and characterization, it is possible to numerically clean contaminated reservoir fluid samples. This paper presents a case study of the effects of Oil-based drilling Mud (OBM) contamination on gas condensates fluid properties from a Deepwater turbidite reservoir in Nigeria. Four contaminated samples acquired from this reservoir were studied. The results show that drilling fluid contamination has a marked effect on key gas condensate fluid properties such as the Condensate-Gas-Ratio (CGR). The higher the contaminant the higher the CGR of the contaminated and resultant cleaned fluid. Numerical cleaning of OBM contaminated gas condensates does not guarantee obtaining a fluid model that is representative of insitu uncontaminated reservoir fluid. A linear relationship was observed between the cleaned fluid CGR and Saturation Pressure (Psat) with respect to the contamination level. Extrapolation of this relationship to 0% wt. contamination yields a CGR and Psat that were likely to be indicative of insitu uncontaminated fluid CGR and Psat. This formed the basis for a low case PVT parameter estimate, thus enabling the definition of suitable fluid parameter uncertainty ranges. The paper also highlights the importance of acquiring multiple fluid samples and benchmarking fluid description against possible analogues within the same and/or similar geological setting to enable the development of possible insights that may support and improve the analysis.