Diffusion of reservoir fluids into the wellbore is known to be a serious well control problem with oil-based drilling fluids. In water-based fluids, the diffusion of reservoir gases is known to be much lower. This section presents the outcome of a study carried out by Technip Offshore Engineering on how reservoir gases diffuse through formate brines. A simple analytical model was developed for the gas diffusion coefficient in aqueous and hydrocarbon fluids. This model was then used to predict diffusion coefficients, diffusion fluxes, and accumulated influx of carbon dioxide (CO₂) from the gas cap into a formate packer fluid and the diffusion flux and accumulated influx of methane (CH₄) through filtrate-invaded formation into a wellbore containing a formate brine.

 

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