Dual-Reamer BHA Eliminates Rathole and Boosts ROP | SLB

Dual-reamer BHA eliminates rathole and boosts ROP

Australia, Oceania

An operator used a BHA with a dual-reamer configuration comprising the Rhino™ multicycle hydraulic underreamer and Rhino™ full-cycle hydraulic underreamer to underream while drilling from the tophole section to the reservoir target in a single run. Not only was a rathole eliminated, but on-bottom ROP was 37.9 m/h.

An operator needed to intersect two reservoir sand targets and run a dual-zone completion to maximize production. Reaching the top of the first reservoir sand from the 13⅝-in casing shoe requires directional drilling a long intermediate hole section within a tight mud-weight window and containing it behind one casing string. Borehole enlargement reduces ECD; hence, underreaming-while-drilling technologies were needed. One underreamer would leave approximately 60 m of rathole if placed above the measurements and logging-while-drilling (MLWD) tools and expose them to greater shock and vibrations if placed near the bit. A long rathole would require a separate cleanout run, while underreaming with MLWD tools in a larger hole size increases the risk of downhole tool failure due to higher bending stresses and shock and vibration. Additional formation challenges included bit-balling tendencies and high stick/slip vibrations in an upper shale. The corresponding formation intervals in offset wells were either shorter (less than 1,500 m), shallower, or required multiple drill bits to reach the casing depth (section TD). This fueled doubts during well planning on whether the long 12.25-in × 13.5-in hole section could be drilled in one run.

Drop-ball-activated reamers can’t be used below MLWD tools, and previous experience with flow-activated reamers had mixed success. Separate applications of reamers experienced by this operator had incidents of unintentional indexing to the “open” position at various phases of the drilling operation. There were also failed attempts of indexing the tool to the desired open or closed position. The challenge of keeping the lower reamer in the “closed” position throughout the run and through numerous pump cycles is crucial, especially for a long hole section where a BHA trip is costly.

SLB recommended deploying a dual-reamer configuration in the BHA. Using the Rhino multicycle hydraulic underreamer as a lower reamer eliminated pumpdown device activation and enabled it to be placed below ID-restricted BHA components, such as MWD and LWD tools. Additionally, the reamer’s flow actuation changes the reaming mode in minutes, reducing reamer activation time and enabling an unlimited number of reliable activation cycles during a run. The operator used the upper reamer, the Rhino full-cycle hydraulic underreamer, to open the 12.25-in pilot hole to 13.5 in while the lower reamer was kept closed. This configuration enabled enlargement of the long interval to 13.5 in while sensitive LWD or MWD tools were confined within the smaller 12.25-in hole diameter, thereby minimizing shock and vibration. At section TD, the Rhino full-cycle hydraulic underreamer was closed with a deactivation ball and the lockout mechanism was sheared off with high flow rate. Positioned above the 12.25-in hole, the Rhino multicycle hydraulic underreamer was indexed to the open position with a set sequence of flow rates, enlarging the remaining 12.25-in hole to 13.5-in hole diameter.

The combined hole enlargement while drilling (HEWD) and rathole elimination (RHE) operation was achieved in a single BHA trip, from the 13⅝-in casing shoe to the target sand reservoir. The hole was enlarged to 13.5 in from 2,506-m to 4,421-m MD. This interval length of 1,915 m is 159 m longer than the best offset run, which was achieved by a 12.25-in drill bit on that well. Not only was the rathole eliminated, but on-bottom ROP during HEWD was 37.9 m/h and competitive with the nearest best offset of 38.9 m/h drilled without any underreamer in the BHA. The customer now has a template on how to reach reservoir targets in the basin using borehole enlargement to deliver hole sizes compatible with production-enhancing completion technologies. The performance of the dual-reamer configuration using the Rhino™ integrated borehole enlargement system serves as the benchmark in underreaming while drilling from the tophole section to the reservoir target.

Rendering of the Rhino multicycle hydraulic underreamer.
The Rhino multicycle hydraulic underreamer provides complete control of reamer activation, eliminating pumpdown device activation.
Products Used