Pore Pressure Prediction and Drilling Challenges: A Case Study of Deepwater, SubsaltDrilling From Nova Scotia, Canada

摘要

Modern day oil exploration pushes operators into harsher andmore difficult drilling environments in the search forhydrocarbon reserves. Eastern Canada is one of thoseenvironments where deepwater and the need to penetratethrough thick salt sheets greatly increase the difficulty facedby drillers. This paper describes a case history of deepwater,sub-salt drilling and examines the requirements for success.This paper also details the challenges, using seismic data, ofpre-well planning for dealing with high pore pressures andvariable fracture gradients. Experience shows that pre-wellengineering differs considerably from conditions actuallyencountered, conditions that require rapid adjustments basedon actual well data. In the case reported here, a fluid influxoccurred at a depth where planning had indicated asignificantly lower pore pressure. This influx directly led tolosing a BHA, sidetracking, and a re-evaluation of the welldata and pore pressure regimes possible at that depth.This paper also highlights the need for flexible welldesigns able to respond to unanticipated drilling hazards andwellbore problems. In the case history reported here, the 11?-in.Casing was set 511m higher than originally planned due topore pressure increases. This decision had a significant effectlater in the well construction program, requiring the use ofexpandable casing, not originally in the well program.This paper illustrates on-the-fly modification of drillingdesigns to rapidly deploy unplanned equipment, the use ofunconventional borehole sizes, and the use of newertechnology such as rotary steerable assemblies for side-trackkick-off. The paper will also discuss the optimised use of holeopeners and expandable casing and the potential effects ofexpandable casing on subsequent hole opener use. Thesedynamic modifications and immediate implementation of lessons learned allowed successful drilling to a record depthfor Eastern Canada.