A roller reamer has historically been included in many bottomhole assemblies (BHAs), primarily to assist in wellbore gauge maintenance. Recently, however, the introduction of an advanced, sealed-bearing roller reamer has made a wider range of applications possible beyond the traditional role of this type of downhole tool.

An advanced-performance roller reamer offers effective torque reduction and vibration suppression, combined with a state-of-the-art compensated sealed bearing and reaming structure that is designed for extended downhole life and reliability. The reamer design also incorporates a range of cutter configurations, including the use of synthetic diamond-enhanced insert technology and the latest techniques in hardmetal application. Cutter configuration options are selected based on the key performance requirements of a BHA.

The adoption of a standard method for the assessment and evaluation of cutter performance was also found to be an important factor in the successful introduction of an advanced performance roller reamer.

Today's challenging drilling environments demand superior performance from all tools in the BHA. Complex and extended reach well geometries require that drilling torque is minimized to improve drilling performance.

Vibration induced while drilling has long been recognized as a significant area of concern. Many of the drilling BHAs used today include sophisticated rotary steerable systems, concentric hole enlarging devices and state-of-the-art Formation Evaluation While Drilling (FEWD) products. The performance and reliability of such equipment can be greatly improved when destructive vibrations are minimized.

As wells are routinely drilled to greater depths, the equipment used in the BHA is expected to endure operating environments with higher pressure and temperature. It is critical that "on-bottom" time is optimized in such applications and unnecessary, costly trips are avoided. The quality of the well bore drilled continues to be a critical issue. The definition of wellbore quality includes several attributes such as:

• In gauge;

• Smooth and free from steps or ledges;

• Free from abrupt doglegs; and

• Free of keyseats

The development and successful introduction of an advanced-performance roller reamer (Figure 1) focused on the provision of a reliable solution to such challenges. The key objectives in the development of the reamer included:

• A greater level of reliability, with an effective sealed-bearing design that would last significantly longer than previously available roller reamers. The sealed-bearing configuration also should exhibit durability and effective pressure compensation in high-pressure, high-temperature (HP/HT) drilling environments.

• A selection of application-specific reaming structures to match the formation characteristics of the well bore. All reaming structures should also include a profile that would facilitate bidirectional reaming.

• The ability to minimize drilling torque. The bearing design utilized should also retain its torque reduction capabilities even in conditions where significant side loading is present.

• The ability to effectively suppress vibrations while drilling, with primary focus on both lateral and torsional vibrations. Operating in such an environment should not compromise performance or durability.

New product features

The development of an advanced performance roller reamer resulted in numerous new product features and improvements over prior designs. In this paper, the more notable new product features have been selected for discussion.

Sealed Bearing Developments. The durability of the roller reamer relies heavily on the integrity of the sealed bearing. It should also be emphasized that the number of revolutions of the sealed bearing elements in the roller reamer will generally be more than three times the number of drill string revolutions for a given interval. The identification of the mechanical forces acting on the sealed-bearing elements during operation is also important. Simulation computer modeling of BHAs was carried out to assist in the development process.

A proprietary elastomer compound was selected for the bearing seals. In laboratory testing, this elastomer was found to be compatible with high-speed applications abd provide greater wear resistance, higher tensile strength, higher temperature rating and compatibility with all widely used drilling fluids. An innovative dual seal configuration was also developed, including both radial and face seals.

The sealed-bearing configuration also included a fully active compensator arrangement. A new, proprietary elastomer was selected for the compensator arrangement, providing greater tear strength and temperature resilience.

The use of a new lubricant was included in the development of the sealed-bearing element. The lubricant selected exhibited an ultra-high viscosity, excellent load carrying capacity and extreme pressure properties. The lubricant was also found to be stable at higher temperatures. An enlarged lubricant chamber was incorporated in the primary shaft of each sealed bearing element and a series of migration ports were added to facilitate lubricant distribution.

Reaming Structure Developments and Options. Application-specific reaming structures were developed to address today's roller reamer performance requirements.

All reaming structures were extended to provide greater surface contact, increasing effective full-gauge reaming life. Laboratory analysis of alternative reaming inserts resulted in the inclusion of a new tungsten carbide (WC) insert grade and the introduction of an optional Synthetic Diamond Enhanced Insert (SDEI). The SDEI structure option is considered to be the ideal selection for highly abrasive applications or when extended run duration is anticipated. For applications where torque reduction or vibration suppression was determined to be the primary concern and less demanding reaming requirements was anticipated, a smoother surface, fluted reaming structure was included as an option.

All retention blocks used in an advanced-performance sealed-bearing roller reamer now include an innovative bi-directional reaming ridge. The ridged profile is created using the latest techniques in laser hardmetal application technology. The inclusion of this reaming ridge on both upper and lower retention blocks provides additional reaming capability in both directions to further extend operational life.

Other Developments. The reamer body geometry was designed to offer greater annular clearance. The cutter retention mechanism now provides primary, secondary and tertiary securing features to provide unparalleled performance reliability.

A new method was developed to safely and reliably remove and install cutter assemblies.

Validation testing and a series of "hostile environment" field tests were successfully concluded. The key test criteria included:

• HP/HT environment;

• Extended run intervals and "on-bottom" time;

• Highly abrasive formations;

• Complex well geometries with high mechanical forces acting on the reamer;

• Runs with frequent shock and vibration; and

• Varied BHA configurations including positive displacement motors (PDMs), rotary steerable systems and concentric hole-enlarging devices.

A set of standard measurements were established to provide a consistent method of dull cutter evaluation. The standard measurements included seal and bearing condition, gauge diameter, and insert condition evaluation. Such types of measurement are widely accepted and used for drill bits but to date have not been routinely used in the evaluation of roller reamer performance.

The spreadsheet shown in Figure 2 provides a summary of the validation testing runs and the subsequent used cutter evaluation results for reference purposes.

Significant performance improvements were noted across the board in terms of seal/bearing longevity and reaming structure durability across the wide range of applications noted.

Computer simulation methodology

BHAs utilized in the validation testing program were also modeled to assist in roller reamer placement and to determine the mechanical forces acting on the roller reamer. In each case, the modeling results were used to ensure that:

• The positioning of the roller reamer in the BHA did not adversely affect the desired path of the well bore being drilled.

• The position selected for the roller reamer was the optimum position to support the BHA in the well bore and assist in the suppression of potentially damaging vibration.

• Side forces and bending stresses at the roller reamer were within acceptable guidelines to maximize operational life.

Examples of simulation outputs are illustrated in Figures 3 and 4. These outputs compare BHA trajectory and show the mechanical forces acting on the BHA. This particular example is discussed in more detail in Case History Example 2.

Case histories

Three case histories have been selected for further discussion. Each case history highlights varied BHA types and objectives.

• Case History 1 discusses a deep HP/HT application.

• Case History 2 is an example of a complex geometry well bore drilled with a rotary steerable system.

• Case History 3 is a simultaneous drilling and hole enlargement application.

In Case History 1, two advanced performance roller reamers were included in an 81⁄2-in. hole size performance drilling BHA. The roller reamers were included primarily to reduce torque and provide BHA stabilization. The anticipated total vertical depth (TVD) of this hole section was approximately 21,000 ft (6,400 m). At this depth, the bottomhole circulating temperature (BHCT) was expected to be 350°F to 375°F (175°C to 190°C). A BHCT in this range was considered to have a significant potential impact on the operational life of the sealed-bearing assembly. Earlier data with conventional roller reamers indicated that a BHCT in this range could result in premature seal failure.

This hole section was successfully drilled using advanced performance roller reamers. The same reamers were used for three consecutive BHAs, accumulating a total of 283 drilling hours, equating to more than 4.7 million cutter assembly revolutions. The sealed bearings and cutting structure were evaluated after this run and were found to be in excellent condition. Dull grading was reported as E-E-E-IN-0. Information provided from the rig site confirms that a significant torque reduction in the range of 35% to 40% was obtained.

In the second case history, an advanced performance reamer was included in a rotary steerable BHA used to drill the 81⁄2-in. hole section of a complex geometry well. In this case, the objective of the BHA was to build angle from 66° to 77° inclination, turn azimuth from 14° to 30°, hold tangent inclination and finally, drop inclination to 45° to intersect the desired target.

The reamer was included in this case to ream an abrasive, interbedded sandstone, minimize torque and suppress vibration. Offset data confirmed concerns with abrasive wear and vibration due to slip-stick. Additional offset data analysis on the performance of conventional sealed bearing roller reamers in this application indicates seal and bearing failure after 900,000 to 2.1 million cutter revolutions.

A mechanical analysis of this planned BHA confirmed that significant side loads and bending stresses were expected to occur at the reamer for the duration of run. The results of the mechanical analysis are referred to in Figures 3 and 4.

This BHA was subsequently used to drill the interval from 9,775 ft to 12,600 ft (2,980 m to 3,840 m) total depth in a single run. All directional objectives were met with this BHA. The well bore gauge was maintained. Occasional tight spots were reamed prior to making connections. Slip-stick was recorded during the run, but no significant shocks were noted.

The accumulated revolutions on the cutter assembly of this reamer were 2.6 million. This represents an improvement of 24% over the comparative offset data.

After completion of this run, the reamer's condition was evaluated. A dull grading was carried out on the cutter assemblies and noted as E-E-F-2-2.

In the final case history, a revised casing program in a deep HP/HT well resulted in the requirement for an extended hole-enlarging section, with the well bore to be enlarged to 14-in. diameter with a concentric hole enlarging device simultaneously while drilling a 121⁄4-in. pilot hole. The depth interval to be enlarged was from 15,610 ft to 17,240 ft (4,760 m to 5,260 m).

Two advanced-performance reamers were included in this BHA, the first being above the FEWD system and the second placed higher in the BHA, approximately 45 ft (14 m) above the concentric hole-enlarging device. The reamers were included to minimize torque and vibration during the simultaneous drilling and hole enlarging operation.

As in previous cases, the BHA configuration was analyzed to assess the magnitude of the mechanical forces acting on it during the planned run. This BHA successfully simultaneously drilled and enlarged a 1,630-ft (497-m) interval in 271 hours. The BHA was pulled to lay down the rotary steerable system. Torque generation was maintained within acceptable levels of 12,000 to 15,000 ft/lbs. No significant shock or vibration was noted for the duration of this run. An evaluation of the reamer cutters after this run noted that all seals and bearings remained effective. This was after an extended run, withmore than 5.7 million accumulated revolutions. The dull grading results were recorded as E-E-E-1-1.

Conclusions

Application-specific reaming structures, proven torque reduction and vibration suppression have broadened the uses of a roller reamer in the BHA.

Design improvements in sealing technology and bearing configuration have resulted in improvements in durability and reliability in deep HP/HT and complex well profiles.

The introduction of SDEI reaming structures has resulted in extended reaming gauge life in harsh, abrasive environments.

Computer simulation modeling of the roller reamer(s) in the BHA has been shown to be a valuable tool in optimizing both reamer and overall BHA performance.

A standard method and criteria established to evaluate used reamer cutter condition resulted in consistent performance measurement. Future product improvements will also be facilitated by the use of this information.

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