Optimization Work Flow Converts Power to Performance for GOM Drilling

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 29065, “Converting Power to Performance: Gulf of Mexico Examples of an Optimization Work Flow for Bit Selection, Drilling-System Design, and Operation,” by Mark W. Dykstra, SPE, Miguel A. Armenta, SPE, Fitzerald A. Mathew Ain, SPE, Omolara Adesokan, and Tess L. Schornick, Shell, and Ashabikash Roy Chowdhury, SPE, and Mark D. Allain, Baker Hughes, a GE company, prepared for the 2018 Offshore Technology Conference, Houston, 30 April–3 May. The paper has not been peer reviewed. Copyright 2018 Offshore Technology Conference. Reproduced by permission. Time spent on bottom drilling is only approximately 10% of the time consumed by drilling operations, but this still provides a significant opportunity for savings if it can be reduced. The goal of the work described in this paper was to decrease this percentage while drilling an exploratory well in the Gulf of Mexico. Significant results were achieved with the use of advanced hybrid polycrystalline-diamond-compact/tungsten-carbide-insert (PDC/TCI) bits. Introduction The focus well is in the Walker Ridge area approximately 150 nautical miles south of Port Fourchon, Louisiana. The rig floor to the zone of interest includes 6,500 ft of water, 1,200 ft of sediments, 12,250 ft of salt, and then deeper sediments. In the basic well design, a 38-in. conductor would be jetted to 200 ft below the mudline. The 26-in. section would be drilled through sediments and 2,000 ft of salt without risers using seawater and a 9.3-lbm/gal water-based pump-and-dump (PAD) drilling fluid, after which the 22-in. casing would be set. The 16½-in. section would be drilled through the bulk of the remaining salt with a riser in place using synthetic-based drilling fluid. The well would remain vertical until the kickoff point. After setting a 14-in. casing, the remaining hole sections would exit the salt and penetrate the deeper zones using synthetic-based drilling fluid. Design Phase: Offset Well Study The first step in the optimization process was to evaluate the drilling challenges that could be encountered in each hole section and identify potential performance limiters. The key lessons from the analysis of offset wells include the following: The shale/sand sequence above the salt would be soft and could be drilled as quickly as desired, though subject to wellbore stability and hole-cleaning limitations. The salt section would be very drillable, but mechanical specific energy (MSE) levels would be approximately 40 ksi. PDC bits would be very aggressive, so torque would be highly sensitive to weight on bit (WOB). Peak rate of penetration (ROP) in both salt and sediments would be directly proportional to the power provided to the bit. Torque variation could be as low as 10 to 20% for stiff drillstrings featuring 65/8-in. drillpipe using relatively high rotary speeds (e.g., 170 rev/min or greater). Bottomhole assembly (BHA) designs with a minimal tendency to hang up are desirable.