UBD Technique Overcomes Geological Uncertainties, Leading to a Production Improvement of 10 Times While Saving 3 Days Rig Time

Abstract

Underbalanced drilling technology in a nutshell contrasts with conventional overbalance drilling due to fact that the bottom hole circulating pressure (BHCP) exerted by the drilling fluid is designed to be intentionally lower than the reservoir pressure. As a result of this pressure imbalance reservoir fluid oil, water or gas (contained within the pore space) is introduced into the wellbore and returns to surface along with the drilling fluid. Where upon the various different fluid streams are separated accordingly. Hydrocarbon gas may be flared off along with any nitrogen (the inert gas injected to lighten the fluid column and induce the underbalance condition). The produced liquid which may contain formation water along with oil will be separated using a 4-phase separator along with the drilled cutting. The cuttings may need to undergo further treatment to remove any residual oil in compliance with any environmental regulatory requirements before they can be adequately disposed of. The base fluid once treated can be reused. [1] Underbalance drilling was deployed across several geographies and interest in this methodology peaked during the 90s where it was combined with new drilling techniques and technologies in the form of horizontal drilling to mitigate common drilling problems such as lost circulation as well as observing productivity improvements. [2] Its use continued across brownfield developments and was deployed across unconventional reservoirs where conventional drilling techniques and reservoir evaluation methods were ineffective. Typical evaluation tools such as logging, coring and seismic that are instrumental across conventional reservoir development and characterization were inadequate in low permeability tight gas reservoirs. A shift to dynamic flow data was needed. Under Balanced Drilling (UBD) by its very essence eliminates any formation impairment uncertainty from the evaluation provided that underbalance condition is maintained throughout operations. [2]