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

Pore Pressure Prediction and Drilling Challenges: A Case Study of Deepwater, Subsalt Drilling From Nova Scotia, Canada Christopher Neil Marland; Christopher Neil Marland Halliburton Co. Search for other works by this author on: This Site Google Scholar Simon Mark Nicholas; Simon Mark Nicholas Halliburton Co. Search for other works by this author on: This Site Google Scholar Wayne Cox; Wayne Cox EnCana Corp Search for other works by this author on: This Site Google Scholar Chris Flannery; Chris Flannery Murphy Oil Corp. Search for other works by this author on: This Site Google Scholar Bruce Thistle Bruce Thistle Nexen Inc Search for other works by this author on: This Site Google Scholar Paper presented at the IADC/SPE Drilling Conference, Miami, Florida, USA, February 2006. Paper Number: SPE-98279-MS https://doi.org/10.2118/98279-MS Published: February 21 2006 Connected Content Related to: Deepwater, Subsalt Drilling From Nova Scotia, Canada - Case Study Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Marland, Christopher Neil, Nicholas, Simon Mark, Cox, Wayne, Flannery, Chris, and Bruce Thistle. "Pore Pressure Prediction and Drilling Challenges: A Case Study of Deepwater, Subsalt Drilling From Nova Scotia, Canada." Paper presented at the IADC/SPE Drilling Conference, Miami, Florida, USA, February 2006. doi: https://doi.org/10.2118/98279-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE/IADC Drilling Conference and Exhibition Search Advanced Search AbstractModern day oil exploration pushes operators into harsher and more difficult drilling environments in the search for hydrocarbon reserves. Eastern Canada is one of those environments where deepwater and the need to penetrate through thick salt sheets greatly increase the difficulty faced by 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, of pre-well planning for dealing with high pore pressures and variable fracture gradients. Experience shows that pre-well engineering differs considerably from conditions actually encountered, conditions that require rapid adjustments based on actual well data. In the case reported here, a fluid influx occurred at a depth where planning had indicated a significantly lower pore pressure. This influx directly led to losing a BHA, sidetracking, and a re-evaluation of the well data and pore pressure regimes possible at that depth.This paper also highlights the need for flexible well designs able to respond to unanticipated drilling hazards and wellbore problems. In the case history reported here, the 11¾-in. casing was set 511m higher than originally planned due to pore pressure increases. This decision had a significant effect later in the well construction program, requiring the use of expandable casing, not originally in the well program.This paper illustrates on-the-fly modification of drilling designs to rapidly deploy unplanned equipment, the use of unconventional borehole sizes, and the use of newer technology such as rotary steerable assemblies for side-track kick-off. The paper will also discuss the optimised use of hole openers and expandable casing and the potential effects of expandable casing on subsequent hole opener use. These dynamic modifications and immediate implementation of lessons learned allowed successful drilling to a record depth for Eastern Canada.IntroductionThe Weymouth A-45 well is located approximately 160 miles South by South East from Halifax, Nova Scotia, Canada, in the deepwater area of the Scotian Shelf. Pre-well seismic analysis identified the presence of a subsalt anomaly, the 1507m thick Argo Salt sequence. This sequence presented, a potential major drilling challenge and also a significant problem in pre-well pore pressure and fracture gradient planning. The well incorporated a complex well design using concentric hole openers and an unconventional casing design in order to successfully complete the well. The well design was planned in response to the challenges posed by the deepwater environment and the thick salt deposit and their combined effect on overburden and fracture pressure. The impact of these factors combined with limited drilling pressure margins --- based on expected pore pressure increases --- required a more complex borehole and casing design. Despite the potential hazards and complex well design, the drilling program allowed for flexibility in the decision processes and in well design changes, to deal with problems encountered but also to extend drilling successes. Flexibility was particularly important when drilling through the salt body with a point-the-bit rotary steerable system. Although the rotary steerable system was not planned for use below the salt, the success of the system in the shallower parts of the well led to its subsequent use below the salt and highlighted the flexibility of rotary steerable technology. Keywords: drilling operation, borehole, wellbore integrity, pore pressure, Wellbore Design, salt body, Upstream Oil & Gas, Nova Scotia, drilling margin, hole size Subjects: Wellbore Design, Drilling Operations, Wellbore integrity This content is only available via PDF. 2006. IADC/SPE Drilling Conference You can access this article if you purchase or spend a download.

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