Managed-Pressure-Drilling Technology Succeeds in the Harding Field
Authors: Carpenter Chris 
Published: February 2015

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 166170, ’Managed-Pressure Drilling, Casing, and Cementing Enable Success in Conventionally Undrillable Wells in the Harding Field,’ by Mohamed A. Mashaal, Tom Fuller, Chris J. Brown, and Robert Paterson, BP, prepared for the 2013 SPE Annual Technical Conference and Exhibition, New Orleans, 30 September-2 October. The paper has not been peer reviewed.

This paper presents a case history of a North Sea well in which managed-pressure drilling (MPD) was used as the enabling technology to drill, case, and cement the well, with particular focus on the planning process, design methodology, and execution particulars. A novel fluid-pressure- transmission pill (FPTP), composed of a crosslinked polymer, was also used to maintain hydrostatic pressure while tripping bottomhole assemblies (BHAs) and during deployment of the liner and sand-control equipment.

Background and Drilling Challenges

The Harding field is a mature North Sea platform development upon which an infill-drilling project has been initiated to access the remaining oil. This oil tends to lie in more-distant, hard-toreach targets, including those in the far north of the field and a new field located south of the platform. These would be accessed by extended-reach-drilling (ERD) wells. A combination of reservoir depletion and weak interbedded sands and shales has resulted in a further reduction in the already narrow mudweight (MW) window between fracture and formation-collapse pressures. The window had decreased from 2 to 0.7 lbm/gal, equivalent to a 200-psi bottomhole- pressure (BHP) window. ERD to access the oil accumulations most distant from the platform would generate equivalent circulating densities that are 50% greater than the available MW window, so these wells are not conventionally drillable.

After MPD proved to be an effective strategy for a test well (IC6) in the Harding field, the decision was made to apply MPD to two ERD wells (PNE4 and PNE2) that had not achieved their objectives. A subsequent investigation into the shortcomings of these wells led by the subsurface team resulted in a reworking of the pore-pressure/fracturegradient predictions for the northeast of the field, taking the depletion in that part of the reservoir into account. Sand/ shale interfaces at the margins of the reservoir, and sand/sand interfaces created by the injection of sand through the main reservoir body, also appear to result in localized fracture-gradient reduction. These combined factors resulted in a reduced MW window compared with that previously used in well planning. Hydraulics modeling strongly suggested that drilling PNE2a (the redrill of PNE2) would be unachievable conventionally, and drove the decision to use MPD for the reattempt. PNE2a would include a 12¼-in. overburden section, a highly challenging prospect containing more than 6,000 ft of shale, as well as the 8½-in. reservoir section, which was expected to have significant sections of shale where instability had previously caused drilling problems (see Fig. 1).