An approximate theory of static filtration of drilling muds in vertical wells

The adverse effects of filtrates during oilwell drilling may be reduced if the mechanism of filtration through mud cakes is well understood. Considerable efforts have therefore been made through empirical and theoretical studies to formulate a robust filtration theory for predicting the effects of mud parameters during drilling. Most of the existing models are either too simplistic or rather complex. This study developed a robust approximate analytical filtration theory that incorporated steady state and transient effects. The results show that in addition to viscosity, transient effects during filtration greatly affect cake build-up and filtrate volumes and that reduced filtrate volumes can be achieved when steady state is achieved rather than unsteady state filtration process.