An examination is presented on the invasion of a hydrocarbon bearing formation by drilling fluid filtrate, and investigates, with the aid of a numerical model, the significance of capillary forces on the resulting displacement. It is observed that in high permeability zones, capillary inhibition can draw filtrate into the formation faster than it is lost through the filtercake, which is assumed to control the fluid loss rate. On the basis of conclusions drawn from the numerical study, the phenomena of supercharging (the difference between the water phase pressure at the sandface and the undisturbed formation pressure) has been reanalysed, and an equation recognising supercharging as a two phase problem is presented. Depending on the character of the displacement, supercharging in a hydrocarbon zone can be enhanced or reduced due to the presence of mud filtrate.
|Title of host publication
|59th Annual Technical Conference and Exhibition (Society of Petroleum Engineers of AIME)
|Published - 1984