This paper presents and discusses the results of the first six field deployments of a newly enhanced 7-in. steerable drilling liner system in Alaska's Greater Mooses Tooth (GMT) project. The system was operated with a managed pressure drilling service and drilled three-dimensional directional objectives while casing an 8?-in. hole section through a highly unstable overburden section to the top of the reservoir section. The shales of the overburden section were chaotically disturbed by a prehistoric landslide that left large sections in unknown orientations from the original bedding planes. These sections have subsequently proven mechanically unstable when drilled at high angles. Exploration wells in the area determined that conventional drilling and casing methods would not allow successful completion of development wells. To succeed, the GMT project needed systems that would guarantee reservoir access and well mechanical integrity. The operator elected to deploy the newest version of the steerable drilling liner system because its design indicated a higher performance potential with more fail-safe options to manage the risks presented by this interval. The new system uses a 4?-in. pilot bottomhole assembly (BHA) and an expandable underreamer capable of opening the pilot hole from 6-in. to 8?-in. for the 7-in. liner that is run in parallel with the drillpipe. The underreamer blade design was customized for the application to minimize drilling dysfunctions and optimize penetration rates. Special operating procedures were applied to deploy managed pressure drilling, surveying with a measurement while drilling (MWD) tool below a motor, and drilling with up to three cutting structures engaged at the same time. A new liner cementing concept was developed and proven to enhance reliability and provide flexibility for various contingency options. The high-risk overburden sections were simultaneously directionally drilled and evaluated with logging while drilling (LWD) measurements while they were secured with the liner to the top of the pay section below. In the first two wells, the planned 18-day deployment was completed in nine days. The duration for the drilling part of the operation planned for 10 days was completed, on average, within 2.5 days without any tool failures or high dynamic dysfunctions while averaging a rate of penetration (ROP) of 35 to 45 ft/hr. Acceptable cementation of the liners was achieved on both wells with bond results comparable to conventional cementing in the section. This paper summarizes and describes the results and system features in detail, and demonstrates how they can help operators reducing operational risks and saving cost.
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