Overcoming Weight-Transfer Challenges in Complex, Shallow, Extended-Reach Wells on Alaska's North Slope

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 19550, "Overcoming Weight- Transfer Challenges in Complex, Shallow, Extended-Reach Wells on Alaska's North Slope," by Randy Thomas, SPE, Dennis Hartwig, and Steve McKeever, SPE, ConocoPhillips Alaska; Dave Egedahl, SPE, ASRC Energy Services E&P Technology; John Patton and Keith Holtzman, Halliburton-Sperry Drilling Services; and Lee Smith, Halliburton-Security DBS/ Alaskan Energy Resources, prepared for the 2008 Offshore Technology Conference, Houston, 5-8 May. The paper has not been peer reviewed. The complex wells constructed to develop the West Sak field on the North Slope of Alaska are approaching the limits of extended-reach-drilling technology. With the shallow vertical depth and long horizontal departure of these wells, transferring weight effectively while drilling and running tubulars can be very challenging. These challenges and the tools, techniques, and learnings used over the past 7 years to solve weight-transfer challenges in this remote environmentally sensitive area are discussed. Introduction The The West Sak field is part of the Kuparuk River Unit on the North Slope of Alaska (Fig. 1). The West Sak heavy-oil sands contain highly viscous, low-API-gravity crude (10 to 22°API) at low reservoir temperatures [result of the extreme northern latitude and the shallow (3,000 to 4,000 ft) burial depth below 1,800 ft of permafrost in the overburden]. The reservoir has three primary sandstone targets, which are very-fine- to fine-grained single and amalgamated sandstone/siltstone beds. Geologic challenges while drilling include numerous fault crossings along the wellbore and random encounters with calcite-cemented spheroids, also known as concretions (Fig. 2). The concretions are much harder than the reservoir sand, having compressive strength of 25,000 psi vs. 500 psi for the reservoir sand. These concretions drill much more slowly than the adjacent sand, which accelerates wear on the bit, the bottomhole assembly, and the drillstring. This difference in hardness can cause the drill bit to deflect off the concretions, resulting in severe unwanted doglegs. Such doglegs make it difficult to maintain directional control, often increasing torque and drag, and can cause downhole-tool damage. West Sak Well Design The primary constraints on West Sak well design are as follows.The shallow vertical depth of the reservoir sands.The need for lateral azimuths to be only to the north or south (parallel to the natural faults)The need for precise lateral placements because of spacing requirements of the waterflood depletion planThe need to drill the laterals in-zone by use of real-time geosteeringThe need to avoid collisions with nearby wells drilled from the same gravel pad