Investigation of mud filtrate invasion using computational fluid dynamics
Despite continued research and developments in logging technology, logs processed by the prevalent standard methods continue to be influenced by formation damage and mud filtrate invasions. The mud-filtrate invasion and related formation damage due to drilling fluids can result in the misinterpreted values of rock and fluid properties in the reservoir which can affect the well plan. Well planning with accurate information of target reservoir is a very important part of any drilling procedure, as it would not only optimize drilling operation and completion but also maximizes production of oil and gas.
To produce hydrocarbons effectively, the wellbore must communicate with formations beyond the altered zone and this can be accomplished by using proper perforations, penetration or creating fractures. Thus, the prediction of invaded zone is critical and a numerical model can be employed for preplanning purposes.
In this study, the dynamic filtration process and the related penetrations into the gas and oil bearing reservoirs were studied in a vertical open hole system using a Computational Fluid Dynamics (CFD) software package. The radius of filtrate invasion was determined by the unsteady-state three-dimensional multiphase fluid flow model. The communication between fluids and formations during drilling and the effects of formation porosity and permeability, time, and overbalanced pressure were investigated extensively. Non-Newtonians drilling fluids such as Bingham plastic, Power-law, and Herschel-Bulkley fluids were also considered for the study. The Mud filtrate invasion in a multi-layer reservoir model and effect of hydraulic fracturing operations were examined.
The results provide an insight on the formation damage around wellbore and related reduction in the hydrocarbon flow due to altered fluid saturations. The importance of accurate prediction of damaged zone around the well bore for the purpose of drilling fluid design, log interpretation, hydraulic fracturing and well completion is explicit from the results.