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Development and Testing of a High-Power, Slim-Hole Drilling System
Project Number

To increase the rate-of-penetration (ROP) in slimhole drilling.

Objective: This project builds, in part, on results from prior R&D with the Gas Research Institute (now the Gas Technology Institute). The previous effort consisted of a basic motor and bit design, and other fundamental research. This effort consisted of motor (slimhole, multi-lobe) redesign to fully utilize the cutting capability of thermally stable diamond (TSD) and polycrystalline diamond compact (PDC) bits. The development of this motor and bit are critical to overcoming problems such as twist-offs and slow drilling rates associated with existing rotary slim-hole systems.


Maurer Engineering, Inc.

Accomplishments (most recent listed first)

The motor/bit combination was designed, fabricated and extensively tested in the laboratory (bench-scale) to assure performance of the system. Field testing at Amoco’s Catoosa Field Test Facility was conducted in February 1996. The high-power slim-hole motor was combined with the hybrid PDC/TSP bit to drill from a depth of 619 feet to 1,446 feet. A variety of formations were encountered having compressive strengths of 4,000 psi to 29,000 psi. Softer formations were drilled at rates of 125 to 150 feet per hour (fph), comparable to conventional aggressive PDC bits. Conventional PDC bits cannot drill the very hard Mississippi Lime formation found near the bottom of the section at Catoosa, but the hybrid bit and motor drilled 40 feet into the formation at rates of up to 25 fph.

The first “real” field test of the high-power slim-hole system was conducted outside Bryan, Texas in the Carroll-Biering Unit No. 1 well. The test consisted of a re-entry to drill a horizontal section in the Buda formation. The kick-off and drilling of the curve sections of the well was carried out using conventional short directional mud motors. Once the horizontal section was reached, the conventional motor was pulled, and the high-power slim-hole system was run into the well. The motor and the bit were run into the well at 10,447 ft measured depth and drilled for 33.5 hours to a measured depth of 11,020 ft. Overall penetration rate was 17.1 fph over the 573 ft interval drilled. Weight on bit ranged from 5,000 lbs to 8,000 lbs and flow rates through the motor ranged from 100 to 140 gallons per minute (gpm).

Results of this project and the associated field test showed that a slim-hole drilling system comprised of a high-power mud motor and hybrid bit can be manufactured that has the ability to drill faster and have long life. This system overcomes many of the problems associated with slim-hole drilling particularly those areas that are most often sited, slow drilling rates and poor BHA life, as the reason slim-holes are not drilled more often.

Current Status
Hybrid PDC/TSP Bit
Hybrid PDC/TSP Bit

and Remaining Tasks: This project was successfully completed. Development of this advanced high-power drilling system is a significant breakthrough that should increase the use of slim-hole drilling in both the oil and gas industries. Reduced penetration rate is currently one of the major barriers to slim-hole drilling. The increased power output from this double length motor will allow higher bit weights and thus increased drilling rates. Many companies are now re-examining the use of slim- hole drilling because of improved slim-hole drilling motors equipped with advanced thermally stable diamond and polycrystalline diamond compact bits. This combination has the potential for reducing well drilling costs by 60 to 75 percent in many areas.

The high-power DOE motor represents a good advancement for performance drilling. This tool can drill faster by delivering more power to the bit. However, commercial motor companies are reluctant to adapt the technology because the increased inventory that they would have to carry. Double length motors would have limited application when compared to conventional motors. The only way to get these companies to make the investment will be to have operators and drilling contractors request the tools.,/p>

The hybrid PDC/TSP bit designs were commercialized by Phoenix Energy Services. These bits drilled over 17,000 ft in commercial runs and showed that the design could drill in many formations that PDC bits could not drill and that in a given run, one of these bits could replace several roller bits; thereby eliminating extra trips. Currently, the bit is not being manufactured because Phoenix Energy Services sold the bit manufacturing portion of the business to a firm that does not make diamond bits. However, this technology is available to the industry. The problem will be to surmount the resistance of the large bit manufacturers to use the developments of a smaller competitor.

Project Start
Project End
DOE Contribution


Performer Contribution


Contact Information

Maurer Engineering, Inc. – John Cohen (713-683-8227 or
NETL – Roy Long (918-699-2017 or