Ongoing advances in under-reaming technology are targeting deepwater wells, where drilling through unstable formations introduces well construction risks. Under-reaming-while-drilling operations help minimize wellbore instability by enlarging the problem zone and allowing more time to run casing before the formation collapses. These operations also ensure that casing or lining reaches target depth so that the well can be completed efficiently.

However, traditional expandable under-reaming systems are increasingly unable to meet the demands of deep offshore wells. These systems do not provide clear confirmation that the cutting blades are activated and fully deployed. In addition, most reamers are activated by ball drop or radio frequency identification (RFID), which limits their placement to the top of the bottomhole assembly (BHA). This can result in a rathole of 30 m (100 ft) or more in length, necessitating a second reaming trip that adds significant expense to the deepwater drilling operation.

These challenges prompted the development of the Baker Hughes GaugePro Echo digital reamer. It is the industry’s first reamer that digitally confirms activation and deactivation. The tool gives operators on-command control and confirmation of blade status and position through downlink communication via mud pulse telemetry or wired pipe.

This avoids the need for a simple shoulder test, in which the extended reamer is pulled against the shoe until the pulling force increases, indicating that at least one of the blades is extended. This indirect measurement does not specify whether all the blades have deployed or if they fully engaged at the desired depth.

Prior to the digital reamer the operator would not know for certain that the hole was properly enlarged until it tripped out and started running casing. If the casing hit an obstruction downhole, it would have to be pulled out for additional reaming runs to enlarge the hole, which is a time-consuming and costly proposition.

Electrical current from the MWD system powers the digital reamer. The blades extend and retract using a hydraulically driven piston that acts independently of drilling parameters such as fluid pressure, flow rate, rpm and weight on bit.

Because it avoids dropping balls or RFID tags, the tool’s metallic body and electrical actuation method means the reamer can be placed anywhere in the BHA. Transmitting data and commands via digital downlink ensures that the reamer is activated in just a few minutes, a significant time savings of more than 30 minutes or longer required for mechanical activation methods.

The downlinkable technology enables operators to send commands to actuate the blades an unlimited number of times. It also sends information on oil pressure, fluid temperatures, and tool vibration and diagnostics in real time.

The system allows drilling and reaming in one run with up to three independent reamers placed in the same BHA. A two-reamer configuration with a main reamer on top of the BHA and a second reamer placed near the bit can minimize the size of the rathole to within 4.6 m (15 ft) of total depth (TD) while eliminating the need for additional reaming trips.

A third reamer added above the main reamer provides additional stabilization. Replacing the reamer’s cutters with stabilization pads that are extended against the borehole serves to minimize excessive vibration or oscillation of the string during the under-reaming operation.

Larger size for greater depth

Reamers in the GaugePro Echo series designed for pilot holes ranging from 6 in. to 14½ in. have been successfully deployed in more than 360 runs. The company has recently released the Series 16 reamer, answering the industry’s need to enlarge boreholes in deep reservoirs ahead of larger outer-diameter casing installations. This larger reamer possesses many of the same design features of the smaller tools in the series but enlarges a 16½-in. pilot hole to a maximum 22-in. hole or any preset size in between.

The new reamer also includes a new five-blade design featuring two more than the industry-standard three blades for concentric reamers. Placing five blades in an optimized layout around the tool body reduces vibration during reaming and provides a more balanced load distribution. These features combined with highly durable Stabilis cutters that are designed to improve impact and abrasive resistance increase the ROP and help ensure a smoother profile borehole.

Early runs deliver

To date, the Series 16 reamer has been run in five wells in Norway and Angola. In each run the reamer successfully enlarged the borehole while exhibiting low vibration at the required running speeds, which helped drillers achieve their desired ROP.

In one of the deepwater Angola wells the operator was drilling a directionally challenging section built to 70-degree inclination. Further complicating the operation, the section was being drilled into an unstable formation where the risk of wellbore instability was high. The operator wanted to optimize the under-reaming process to achieve the desired inclination and deliver a hole with sufficient clearance to accept a 16-in. liner in one run. This also would require minimizing the nearly 61 m (200 ft) of rathole between the drillbit and the main reamer.

Baker Hughes engineers worked with the operator to develop a dual-reamer configuration in the BHA that also would minimize the under-reaming time. The team installed two digital reamers into the BHA, one at the top and the other just above the bit. Each reamer was configured to open the hole from 17½ in. to 20 in. below the 20-in. casing.

The main reamer helped to achieve the desired inclination and borehole size through the unstable formation when drilling began. Once the drillbit reached 61 m (200 ft) above TD, the starting point for the future rathole, drilling was halted and the operator sent a downlink from surface to activate the near-bit reamer. The blades were deployed into the formation, and the cutters started enlarging the borehole near the bit.

With confirmation at surface that near-bit and main reamers were both fully deployed and running, drilling resumed. As the drillbit proceeded to TD, the main reamer enlarged the borehole while the secondary reamer eliminated the rathole, all in the same trip. This was confirmed by real-time log readouts at surface.

This deployment successfully delivered the wellbore with the correct inclination and borehole size to allow efficient running of the 16-in. liner. The simultaneous operation of both reamers replaced the conventional practice of drilling to TD, pulling the drillstring up to the top of the rathole and then activating the near-bit reamer to perform a dedicated rathole-clearing run. This second run would have added three hours of rig time to the operation.

In total, the single-trip dual-reamer operation saved the operator 27 hours of rig time while minimizing the rathole to just a few meters in length. The five-blade design of the Series 16 reamer helped minimize vibration during the run, even as the tool rotated at up to 140 rpm.

The success of these initial runs has spurred other operators to deploy the technology in deepwater regions from West Africa to Brazil in 2017.

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