| Popis: |
Operators frequently use hole enlargement techniques to address drilling challenges, such as pore pressure and fracture gradient windows, ECD reduction, swelling and reactive formations, and tight casing tolerances, and to increase production. Typically, concentric underreamers are run above the logging-while-drilling (LWD) tool to enlarge the hole during drilling operations while providing optimum LWD log quality. Rotary steerable systems (RSS) are normally required in this application to provide full steerability with continuous rotation. The position of the underreamer in the bottomhole assembly (BHA) leaves a long rathole section that is not enlarged. In some cases, this pilot hole must be opened on a dedicated opening run, incurring additional rig time and expense, while the additional formation exposure time can result in deteriorating hole conditions. Long rathole sections can present problems with running casing to total depth (TD), as well as problems of breaking down the formation while cementing. A large international oil company in Norway required a solution that enabled underreaming while drilling and that could provide rathole reduction to less than 20 ft to ensure a good casing seat while eliminating the dedicated run to enlarge the rathole. A new system was developed for this application that enabled underreaming while drilling reducing the rathole to 3 ft for hole sizes from 8 ½” to above 20”. The system includes a conventional or wired underreamer that can be run above the LWD tool or above the RSS, and an at-bit underreamer that can be run below the RSS. The at-bit reamer can be opened by hydraulic or ball-assisted activation. At TD, the at-bit reamer is activated to enlarge the rathole between the upper underreamer and the bottom of the hole, thereby reducing the rathole to 3 ft. The RSS BHA with the at-bit reamer was designed and optimized using BHA modeling software. A balanced BHA design is critical with underreaming operations to minimize drilling dysfunctions. Stabilizer position and fulcrum-point loading were optimized to ensure good directional performance of the RSS while underreaming. A total of nine runs have been performed to date in hole sizes ranging from 12¼×13½ in. to 17½×20 in. Directional work has also been performed, showing good directional control with this system. In the 17½×20-in. sections, a total of 7,569 ft was drilled and reamed in five runs. In the 12¼×13½-in. sections, four runs were drilled/reamed for a total of 19,743 ft. The development of this technology has added new capability to the industry in the optimization of hole enlargement applications. The benefit is realized in a reduced number of days required to drill the well and in reduced total well cost. In addition, getting casing into the hole sooner reduces risk and can help to reduce operational nonproductive time (NPT). |
