Monitoring the real-time down hole equivalent circulating densities (ECD) of parasite aeration can be done quite easily and accurately with a simple spreadsheet calculation. The method is described and field examples are presented comparing the results of this using procedure with pressure while drilling (PWD) data. Situations where using this method may not be accurate will also be discussed.
Parasite aeration involves running a small diameter string of tubing down the outside of the casing string and injecting air to aerate the mud column in the casing to drill pipe annulus to reduce bottom hole pressure. Parasitic aeration is a highly effective method for underbalanced drilling operations which has many advantages over down the drill pipe aeration. These include a lower air injection pressure, independent control of the mud and air injection rates, aeration can continue during connections, different dual gradient pressure profile more like the pore pressure profile for high altitude locations, lower pressure surges after trips or connections, and the unique ability to monitor in real-time the down hole pressure with a simple spreadsheet calculation.