Methodology For Manipulation Of Wellhead Pressure Control For The Purpose Of Recovering Gas To Process In Underbalanced Drilling Applications

摘要

An updated approach to underbalanced well design has beenrndeveloped with a view to enhancing the ability to recover gasrnto process (pipeline, gas plant, offset well, temporary storage,rnetc.). With the growing trend towards reducing greenhouserngas emissions, this technique evaluates the range ofrnanticipated operating conditions (gas inflow and wellheadrnpressures) as a function of liquid and gas injection rates andrnthe productivity index of the reservoir.rnTypically, underbalanced drilling projects have been designedrnto minimize gas injection requirements down the drill string orrnannulus (concentric injection or parasite injection) forrnequipment efficiency and erosional considerations. Thisrnmeans that wellhead pressure is typically kept to a minimum,rnmaintaining sufficient pressure to aid in shipping liquids fromrnthe separator. An exception to this is where elevated wellheadrnpressures may be desired to increase bottom hole pressure andrnreduce inflow from the reservoir, however, the objective inrnthis instance is to control bottom hole pressure.rnThe typical approach to designing for underbalanced drillingrnparameters is normally based upon a graph of bottom holernpressure on the y-axis as a function of gas rate on the x-axis.rnIt is usual to overlay the hole cleaning parameters – basedrnupon minimum annular liquid velocity – and minimum andrnmaximum equivalent flow rates through the motor. Inrnaddition, the target bottom hole circulating pressure limitationsrn(usually derived as a function of reservoir pressure) define thernoperating window from which the required liquid and gasrninjection rates can be determined.rnThis updated approach addresses many issues such asrnequipment sizing and expected production rates while drillingrnthrough to effective pressure management at surface to aid inrnwell stability. Furthermore, the approach lays down thernfundamental groundwork for future underbalanced controlrnalgorithms.