What is Managed Pressure Drilling?
The first recorded use of managed pressure drilling was in 1866 but it has been in widespread use by the industry for more than 50 years. Managed pressure drilling seeks to manage the hydrostatic head (i.e., the weight or pressure of the drilling fluid column in a well) such that it is near equal to the reservoir pressure. Under these conditions the drilling fluids do not enter the reservoir (the gas reservoir pressure is greater therefore keeping the drilling mud within the well bore) and this prevents the drilling fluids contacting the clays which we know swell when in contact with water. An additional benefit of managed pressure drilling is that the well site surface equipment contains the drilling fluid system within certified equipment and is never exposed to atmosphere so is a key added environmental protection.
CalEnergy successfully utilised managed pressure drilling for the drilling of a 321m sidetrack (a new reservoir penetration drilled at an angle) from within the existing Whicher Range #4 (WR-4) well in 2013. This sidetrack was tested in 2015 and provided encouragement for its natural flow potential.
Normal or ‘overbalanced’ drilling methods deliberately maintain a hydrostatic head that is greater than the reservoir pressure (i.e., the drilling mud is ‘overbalanced’ with respect to the reservoir pressure) to deliberately invade the reservoir with drilling fluid and by doing so come into contact with the clays in the Whicher Range reservoir and causes them to swell. This reduces the natural flow of gas.