Successful lateral well placement using optimal bit design and underreamer with real-time communications

The IUR was tested at the Baker Hughes full-scale rig in Oklahoma.

A new, integrated underreamer (IUR) has been developed, that provides real-time communication via the mud pulse telemetry system. As such, the underreamer can be placed closer to the bit to aid vibration management and minimize rat hole length. The tool reveals the current condition of the tool and the position of the blades (implied hole caliper). Additionally, it uses internal hydraulic oil pumped-pressure for the activation (and deactivation) of the blades.

The IUR was used to drill and underream 6,645 ft in two runs at UK North Sea’s Harding field, totaling 288 hr of on-bottom drilling, with minimal vibrations. The well was drilled with an inclined trajectory of up to 90°, with as much as 5°/100 ft dog-leg severity (DLS). The reamer provided an in-gauge borehole, allowing for successful running, rotation and cementing of approximately 4,300 ft of 7⅝-in. liner without any issues, demonstrating superior borehole quality.

BACKGROUND

A joint development of the IUR was begun in 2007 by Statoil and Baker Hughes. Baker had provided drop-ball, pressure-activated sliding-blade type expandable reamers. It was a natural step to move to remotely controlled, hydraulic-electric reamers, Fig. 1. The first downhole use of the IUR occurred in November 2008 at a Baker Hughes full-scale testing rig in Oklahoma. In that test, the reamer drilled and reamed a hard formation, while opening and closing on demand and testing all fail-safe systems, Fig. 2. The IUR then additionally went through a field testing phase, where it successfully drilled and reamed on seven runs for an operator in Grane field over the next three years, for a total of 21,844 ft drilled and 6,943 ft reamed.

Fig. 1. Field images of the IUR, showing concentric design with stabilization.

INTEGRATED UNDERREAMER

Previous underreaming operations on Harding wells have experienced tool failures, due to vibration and limited activation/deactivation cycles, thus limiting operational flexibility. To mitigate risks and increase possible mode options, it was decided to utilize the new IUR, which was capable of communicating with the surface, opening and closing on command and being placed as close as possible to the bit, to minimize vibrations and the length of non-underreamed rathole. 

REAL-TIME COMMUNICATIONS

The IUR operates with several selectable control modes, sent to the tool via downlinking or wired pipe control.

1. Retract mode. In this mode, the blades are receiving hydraulic force to keep them closed. This is the mode, when tripping in or out of the hole, and when no reaming is anticipated.
2. Reaming mode. This mode activates and opens the reamer blades using hydraulic opening force.
3. Power save mode. If there are MWD power supply problems, the tool will go into this mode, which shuts off power consumption and utilizes the spring retraction fail-safe to retract and hold the blades in closed position.

Continual feedback is transmitted via MWD mud pulse from the IUR to the surface monitoring equipment, Fig. 3. At a minimum, data are provided after every pump or power cycle—closing or opening the tool, making connections, etc. Data include: a) reamer activity mode, indicating what the tool is doing; b) outer diameter being cut (between 8.07 in. and 9.875 in.) with a resolution of 0.1 in. Actually, this measurement is an LVDT (linear variable differential transformer) measurement of the axial position of the blades, inferring the diameter being cut; c) a tool diagnostic indicator showing the current working pressure.

ENGINEERED FAIL-SAFE FEATURES

The IUR has been designed such that under no condition should the reaming blades be activated when they are not desired to be activated. Several fail-safe modes have been designed into the IUR, to ensure that the blades automatically retract in all required situations.

Fig. 2. Composite six-arm caliper plot for the selectively reamed section in the test well at the Baker Hughes test site in Oklahoma. Click image to enlarge.

1. Under normal conditions, when the tool is desired to de-activate, a signal is downlinked to enable the blades to retract through hydraulic force.
2. The IUR monitors the MWD bus data traffic. An adjustable time limit may be reached without any communication to the tool, which will indicate a malfunction. The IUR will automatically react to this condition by triggering the “retract” mode to the blades, where they will hydraulically retract. This feature may be deactivated, if desired.
3. The IUR may be programmed to go into “retract” mode, if the continuous pumping time limit is reached. For example, if it is expected that the rig will be making connections every 90 min., then the IUR may be programmed to automatically retract, if pumps are on continuously for 180 min. Under certain system malfunctions, this would prevent the blades from remaining powered out while trying to trip out of the hole.
4. Whenever the rig pumps are suddenly shut down without signaling the IUR to close, then the IUR is programmed to automatically power down and allow the blade springs to retract the blades. This is the primary fail-safe backup.

These multiple fail-safe features are designed to address any eventuality and prevent the blades from ever locking in an activated position.

BHA CONSIDERATION

The IUR was designed with an integral 8¾-in. stabilizer for a nominally 8½-in. pilot bit. The bit choice is critical as the level of stick-slip is very sensitive to the bit stability and bit face aggressiveness. The pilot bit chosen was a type IADC M223. The same pilot bit was used on both runs. During drilling on the Harding platform with the IUR, no severe torsional oscillations were detected. No tool failures related to vibration were experienced. The ‘open and close on command’ characteristics of the IUR were ideally suited for the project.

Fig. 3. Typical real-time status display screen, broadcast on MWD surface unit, indicating integrated underreamer status, caliper and mode. Click image to enlarge.

MATCHING BIT TO THE REAMER

Due to the fact that a typical rotary or directional BHA will place the reamer several feet behind the bit, the reamer loads can vary greatly, as compared to the bit loads. This can occur for two reasons: 1) bit and reamer are in different formations; and 2) aggressiveness of the bit does not match the aggressiveness of the reamer. One of the considerations of the bit design was to analyze and coordinate the bit aggressiveness to that of the reamer, to more closely balance the loads seen while drilling through homogeneous formations, Fig. 4.

A common but erroneous assumption is that matching the bit to the reamer means having the same cutter size on both tools or following a simplistic set of equations buried in a software program. This assumption does not take into consideration several aspects of the drilling process. Due to the aggressiveness of the bit and reamer, they interact with the formation differently, so drilling dynamics are different. Even mechanical rock properties are different. For example, by the time the reamer starts drilling a new formation, some of the inner formation stresses have been released. The reamer typically has higher aggressiveness than the bit.

Fig. 4. Bit and integrated reamer synchronization.

A team was formed to address the issues identified on the IS-6 well and provide a solution. The entire drilling system environment (BHA design, reamer, bit, formations, drive mechanisms, etc.) was taken into consideration. The main challenge was to eliminate or reduce the pilot bit out-drilling the reamer. By doing so, much of the lateral and whirl vibrations could be reduced (Thomson, et al, 2008). Likewise, preventing bit drill-off would reduce the risk of lower BHA damage or back-off.

HARDING RUN 1

The Harding, 9/23b-A32Z (IS6) well was designed to be an oil producer, Fig. 5. Shale instability and weak injected sands were some of the known potential issues while drilling the overburden. With tight shale collapse and sandstone fracture gradient windows in the overburden section, proper ECD management was critical for managing the risks and being able to achieve the hole section objective.

The project objective was to ensure smooth drilling dynamics throughout the long overburden section and maintain ECD, while acquiring relevant geological data to help aid lateral mainbore well placement. The intent was to underream to the planned lateral side track point and then close the reamer blades and continue drilling to the section TD.

This IUR has the exclusive ability to downlink with the tool to open or close the reamer blades “on-command” and also to confirm that status to the surface. The tool is also capable of sending the hole diameter measurements to surface. With its several fail-safe mechanisms, the IUR tool stood out when compared to conventional reamers, which featured the ball-drop mechanism. Results were mixed when such ball-drop reamers were used by the operator. Under these circumstances, the operator was keen to try the new technology, with enough safety features, which would ensure successful execution of the drilling operations.

Fig. 5. Schematic of IS1z donor well and well plan for IS6 pilot and IS6 mainbore. Click image to enlarge

The IUR was run-in with a rotary steerable system (RSS) and an 8½-in., six-bladed PDC bit, properly synchronized to the reamer and formation. When drilling commenced, the command was sent for the reamer to open and ream the hole. For a quick confirmation that the reamer was opened correctly, a well-known procedure was carried out to drill several feet with the activated reamer, then pull back circulating and log the increased resistance (hookload) when the opened reamer was pulled into the 8½-in. pilot hole. Measuring the increased resistance indicated the reamer had likely opened. Another method to verify that the borehole enlargement is being reamed correctly is to pull back and log the LWD caliper over an enlarged hole, or even the transition between the pilot and the underreamed hole. This transition can be “seen” by the LWD caliper, indicating successful tool activation.

Real-time visualization of the underreamer’s performance is realized by incorporating the data into surface drilling displays, Fig. 6. These displays show a combination of surface and downhole measured parameters that allow quick evaluation of the current drilling and underreaming status. The real-time display on surface confirmed that the tool was open and activated. Status of the tool and its activation modes were tracked by the operators on surface as well as a team of technical experts in the tool development center in Celle, Germany, via remote monitoring services.

Drilling progressed as planned until the ECD started to gradually increase to critical levels. Various steps were taken to manage ECD such as reducing ROP, flow and RPM; increasing frequency of pumping sweeps, adjusting fluid rheology, and ultimately, a gradual reduction of mud weight to acceptable levels. Therefore, it was decided to keep the IUR activated and open throughout the run to section TD, reaming the full 4,489 ft of the section. The IUR performed well, even with overall high dog-legs, and the tool pulled out with an excellent dull grading of 1-1-WT. In the end, the open-close-open function was not needed, as it had been originally planned. The bit-reamer-BHA synchronization worked very well, with no vibrational issues reported throughout the run.

Fig. 6. Remote real-time monitoring services on the Harding IS-6 well helped to keep track of the IUR’s status. Click image to enlarge.

During the pilot run, one of the fail-safe features of the IUR activated (unintentionally) to momentarily retract the blades inside the tool. The tool was programmed to retract its blades when the onboard diagnostics detects no communications from surface for a programmed interval of time. This is to ensure safe retraction of the BHA through the casing, in case of tool or downlink failure. Once the blades retracted, ROP increased momentarily and the IUR tool parameters confirmed the deactivation of blades. A command was sent to the IUR via the downlink to reactivate the blades and resume underreaming the small part of the hole section that was missed. Although not planned, this inadvertent activation turned out to be a verification of one of the fail-safe functions.

HARDING RUN 2

Based on the first run, the lateral-hole sidetrack BHA included the IUR, along with an RSS assembly and synchronized drill bit. The reamer performed as expected, delivering the planned well path, and meeting the challenging demands for achieving high dogleg severities. Intermittent minor stick-slip and lateral vibrations were seen while drilling the formation. The plan was to use 2,235 ft of the pilot’s openhole section as a part of the main bore. As the well progressed, approximately 2,000 ft of the pilot openhole interval was utilized in the main bore, as a result of successfully managing the narrow pressure margins, to underream the borehole. The second IUR assembly drilled 2,165 ft to TD and was pulled out with blades dulled at 1-2-WT. Overall, the integrated reamer run achieved the objectives without any noteworthy issues. Again, the “open-close-open” function was not needed. Reaming in this manner on both the wells allowed the 7⅝-in. production liner to be run to bottom with relative ease.

CONCLUSIONS

• The IUR reamed a full-sized enlarged borehole for the Harding IS6 well, as the liner was installed easily and without incident.
• The synchronization of the bit to the reamer was successful, since vibrations were close to non-existent during Run 1 and were minor during Run 2. This allowed for good ROP and no BHA vibration damage.
• On Run 1, the reamer blade wear was dull-graded as minor at 1-1-WT, on a zero-to-eight severity scale. On Run 2, the blade dull grade was also very good at 1-2-WT.
• The IUR achieved the designated objective—underreaming the pilot well and lateral well on Harding. During Run 1, it recorded its longest run: 4,480 ft of underreaming distance, in 194.6 hr of drilling time with a maximum DLS of 5.07°/100 ft and up to 90° inclination at TD. Run 2 also made the distance of 2,165 ft to TD in the lateral hole as planned, without vibration being a dysfunction.
• The IUR opened and closed, as needed, upon instruction from the rig floor via downlinking.  

ACKNOWLEDGEMENTS

This article was adapted from SPE paper 170599, presented at the SPE ATCE held in Amsterdam, The Netherlands, Oct. 27-29, 2014. The information contained herein concerns drilling activities undertaken in relation to the Harding asset in December 2012. Ownership of the BP Exploration Operating Company Limited interest in the Harding asset was transferred to Taqa Bratani Limited on June 1, 2013. This information is, accordingly, issued with the kind permission of Taqa Bratani Limited and its Harding co-venturers.

REFERENCES

1. Pragt, J.; W. Herberg, M. Meister, C. Clemmensen, G. Grindhaug and K. Hanken, “Reaming on demand—selective activation of an integrated underreamer at the Grane field in the North Sea,” SPE paper 146501, presented at the SPE Deepwater Drilling and Completions Conference, Galveston, Texas, June 20-21, 2012.
2. Thomson, I.; S. Radford, J. Powers, L. Shale, and M. Jenkins, “A systematic approach to a better understanding of the concentric hole-opening process, utilizing drilling mechanics and drilling dynamics measurements recorded above and below the reamer,” SPE/IADC paper 112647, presented at the SPE/IADC Drilling Conference, Orlando, Fla., March 4-6, 2008.
3. Voss, W.; J. Aslakson, I. Thomson, S. Radford, C. Thomson and B. Buxton, “Total system optimization delivered significant performance improvement and cost savings in GOM challenging salt section,” IADC/SPE paper 128901, presented at SPE Drilling Conference and Exhibition, New Orleans, La., Feb 2-4, 2010.