Innovations in drill bit design continue to improve performance.

During the last decade, diamond bits have taken market share away from tricone roller bits. Today, polycrystalline diamond compact (PDC) bits account for nearly one-third of the total worldwide bit market, with annual sales exceeding US $200 million. PDC bits are figuratively worth their weight in gold, especially in deep wells. Even though a single PDC bit can cost up to $40,000, it can save the operator $100,000 or more when drilling deeper wells because it saves drilling rig time.

"In today's drilling environment, it is important to save time, eliminate as many unnecessary trips as possible to reduce overall drilling cost and improve overall drilling safety," said Jack Castle, chief operating officer at RBI-Gearhart. Therefore, choosing the correct bit for the job can be one of the most important decisions in drilling the well.

New PDC bits drill the impossible

Smith Bits has focused on the development of highly specialized PDC bits geared towards the industry's most problematic applications, including salt drilling. Specialized PDC bits also have been engineered for hard and abrasive formations that previously were considered non-drillable with that type of bit.
"Successes in salt drilling applications have been very sporadic - especially large hole sizes greater than 10 in. - due to directional and vibrational issues," said Graham Mensa-Wilmot, director of technology development at Smith Bits. "Highly passive PDC bits with high blade counts, small cutters and high back rakes severely compromised rate of penetration (ROP)." Even when successful technically (ROP less than 20 ft/hour or 6 m/hr), the performance of such bits compromised operational efficiency, resulting in high overall drilling costs, he said.

The introduction of rotary steerable tools helped address most of the directional concerns associated with this application. However, the vibration issues, which have a direct bearing on ROPs and thus operational efficiency, still needed to be addressed. Smith Bits has introduced a new-generation PDC bit that was developed specifically to address the dominant vibration modes associated with salt drilling, thus ensuring significant ROP improvements. "With these bits, ROP in excess of 100 ft/hr (31 m/hr) are being achieved in large hole-size salt applications with minimal vibration concerns," Mensa-Wilmot said.
When drilling hard and/or abrasive formations, the industry usually has defaulted to impregnated or insert-type roller cone bits. Impregnated bits exhibit the durability needed to drill such rock, but are operationally challenged from an ROP perspective, especially when shales and/or argillaceous formations are encountered. Insert bits usually drill faster than impregnated bits but lack the durability needed for such applications.

Smith's new PDC bit (Figure 1) combines the ROP and durability advantages of insert and impregnated bits. The concepts incorporated in this bit are based on the behavior and response of hard and abrasive lithologies to different operational parameters such as weight on bit (WOB) and RPM. These specialty bits have been engineered to be effective in high RPM environments, such as deep or high-pressure, high-temperature wells, where turbo-drills frequently are used.

Specialized PDC cutters (Figure 2), with extremely high abrasion-resistance characteristics also have been developed to complement the performances of these special bits for hard and abrasive formations.
Application-specific PDC bit design

Halliburton says it took sophisticated analytical tools and advanced development capabilities to create the FASTER Series of application-specific PDC bits. The company's Security DBS product service line has new FM3000 bit technology that not only incorporates FAST technology features already proven to enhance bit stability, but also incorporates the superior ELITE Series PDC cutting structure designed utilizing new Rock Cutting Analytical Tools. This combination has created a step change in PDC bit design.

The Rock Cutting Analytical tools include a 3D Wear Curve, an improved

force balancing model, a transition drilling model and patent-pending technologies for energy lateral forces. Even axial forces are considered, in effect neutralizing the summation of all cutter forces. Energy balancing capabilities allow more detailed analysis of individual cutting forces and distribution of those forces across the bit face.

In addition, the patented Transition Drilling method is a key advantage of the FM3000 Series technology, as it allows design of bits that can withstand the rigors of drilling through vastly changing rock compressive strengths. Using the model, drastic changes in rock strength can be drilled in a virtual simulation, providing essential design data.

The significant improvement in performance of the FM3000 Series is due in part to the Elite Series PDC cutter technology. The Elite Series of thick diamond PDC cutters feature proprietary interface geometries that afford double, triple and quadruple the diamond carat weight of standard PDC cutters. The Elite Series technology has overcome the historical drawback of reduced impact resistance associated with thicker diamond tables. The new PDC cutters provide significantly greater impact resistance as a result of process improvements that include new manufacturing techniques, design analysis and testing techniques.

The FASTER combination of innovative design capabilities and analytical tools makes the FM3000 Series one of the industry's most advanced application-specific PDC bits. And as with engagement rings, the bigger the diamond, the better.

New HedgeHog technology introduced

Hughes Christensen recently introduced a new type of diamond-impregnated drill bit. Called the HedgeHog, it is expanding the application range of surface-set diamond technology into formations traditionally drilled with tricone bits.

Historically, the use of impregnated bits has been restricted to hard and abrasive sandstone formations, whereas PDC bits performed best in softer, non-abrasive rock. However, in common formations of hard, abrasive sandstone interbedded with soft shale, neither tricone nor PDC bits delivered satisfactory performance in terms of penetration rate or bit life.

The initial goal of the HedgeHog was to increase the flexibility of impregnated bits to maintain high ROP and long bit life in hard and abrasive formations (25,000 UCS), but with the added capability of drilling at least 25% faster in softer shale sections. After a worldwide review of impregnated bit performance, Hughes Christensen engineers determined that modifying the cutting structure and hydraulics would limit balling severity in soft formations, while modifying the surface-set diamond material would successfully address varying formation abrasiveness.

HedgeHog features many innovative cutting structure improvements. To improve drilling performance in soft formations, engineers have optimized blade count and added an interrupted cutting structure that allows the bit to drill shale more efficiently. Deep junk slots help reduce balling tendency in soft formations. The bit also features unique post-type cutting structures attached to elongated blades. Both of these cutting elements are impregnated with diamond grit to provide additional cutting material for extended bit life.

By allowing design engineers to select from three different types of diamond matrix and grit combinations, along with three different cone configurations, each HedgeHog bit combines optimum drilling efficiency and durability based on regional requirements. HedgeHog features an aggressive PDC cone in softer applications and an aggressive, yet durable, 45-degree inverted Supercone for most other applications. A variation of the Supercone is used in extremely hard and abrasive applications.

HedgeHog features three new matrix types that cover the entire range of applications:

• R60 - suitable for the most demanding abrasive applications;
• R30 - the mainstay for drilling interbedded formations; and
• R10 - intended for predominantly non-abrasive applications.

To achieve increased performance objectives, hydraulics had to be improved, especially when drilling shale formations. A unique ported design was introduced that has maximized hydraulic energy to the hole bottom and bit face while a small crow's foot cleans the bit's center. Large junk slots enhance ROP by optimizing cuttings evacuation and limiting hole swabbing during trips.

The 6-in. hole section in Hassi-Messaoud, Algeria, was selected for matrix field testing because of extensive performance data from previous bits. The initial test of the new R30 matrix in a standard S280 design set an area record, drilling 820 ft (250 m) at 8.2 ft/hr (2.5 m/hr). The second run was even better: 823.2 ft (251 m) at 12.1 ft/hr (3.7 m/hr). Convinced they had identified the proper matrix, engineers used the new matrix in HedgeHog's innovative post-on-blade cutting structure. The first HedgeHog run was impressive, drilling 888.9 ft (271.1 m) in 215 hours in Algeria's Rhourde Nouss field. The second run at Hassi-Messaoud drilled 1,184 ft (361 m) at an incredible 22.9 ft/hr (7 m/hr), by impregnated bit standards.
In Oman, an 83/8-in. HH356G89Y HedgeHog bit set a new world record for single-run footage when PDO drilled 3,753 ft (1,144 m) in their LNG drilling campaign. Also in Oman, an 83/8-in. DP0443 HedgeHog set a 2001 world record for cumulative footage, accumulating a total of 3,706 ft (1,130 m) in 308 hours while drilling for PDO in the Saih Rawl and Barik fields. Based on dull grading, engineers concluded the bit was in excellent condition and could have continued drilling (Figure 3). The balanced HedgeHog design has proved to be rugged yet flexible enough to solve historic impregnated bit problems of durability and balling.

Rotary steerable PDC bits

The latest PDC design innovation from Diamond Products International (DPI) is the VectraRST Series. This series features a number of design elements that have significant advantages in rotary steerable applications. In motor and rotary steerable drilling, all tools use either a tilt or push action to change bit direction. Controlling side aggressiveness - while maintaining a good rate of penetration - is paramount in these applications.

The VectraRST Series, in both steel and matrix bodied designs, has proven to stabilize the bit significantly and minimize gauge side cutting. Special features such as carbide or PDC knobs placed on the outside gauge, plus strategically placed Tapered Shaped Cutters, have provided unmatched directional control and steerability (Figure 4). Additional benefits include improved hole geometry and longer bit life.
Previous bit runs on rotary steerable systems had reduced ROP at one offshore Nigeria field due to directional changes and problems with hole conditions. After reviewing previous run data and discussions with the operator, DPI provided a "built for purpose" matrix PDC bit with VectraRST design features to stabilize the bit and eliminate spiral hole problems caused by the aggressive side cutting of PDC cutters.

An 81/2-in. VMP69R was used on a rotary steerable system to drill 5,175 ft (1,578 m) of hole in 41.5 hours to TD of the 81/2-in. interval. The bit was pulled virtually green and re-run on another well, which is unprecedented for this type of run. The bit built angle from 12.8 degrees to 87.9 degrees and achieved the required dogleg of 3.7 degrees/100 ft (31 m). This operator was very pleased with the performance, and significant benefits and cost savings were realized as a result of improved steerability, better hole geometry, and the ability to re-run the bit.

Drilling deeper with fewer diamonds

Canadian-based United Diamond is growing rapidly and proving itself in the international arena, where its unique PDC bits are drilling their way through the toughest formations.

U.S. General Manager Doug Smith says United Diamond is a huge success in the United States, where the company's five-blade design concept and different cutter sizes are resulting in optimum depth-of-cut, higher rates of penetration, and enhanced stability and durability.

"The theory behind United Diamond's bit design is that there are an optimum number of cutters required for a particular bit size," Smith said. "These cutters must be mounted to the bit in a pattern that maximizes overall cutting efficiency. Rather than employing more diamonds to increase bit durability - and consequently sacrificing the efficiency of the cutting structure - United Diamond has taken an entirely different approach to its product design. The bit profile and the cutter orientation and location help reduce drilling-generated vibrations and create a constant torque, which makes the bit more stable."

Anadarko Petroleum ran a 97/8-in. UD513, five-bladed PDC in Anderson County, East Texas. PDC drill bits in offset wells drilled this same section at 69 ft/hour (21 m/hr), with two costly trips needed to reach the top of the Travis Peak. The UD513 bit drilled from surface casing drill-out to the top of the Travis Peak at 81 ft/hour (25 m/hr).

Anadarko runs mud motors to increase the performance, penetration rate and life of the drill bits. On this well, a 7/8 lobe, extended power section motor was run. Utilizing the UD513 and this motor Anadarko was able to save 31 rig hours in trip time and increased penetration rate.

Petrobank, operating as Petrominerales Colombia Ltd., was drilling its first well in Colombia, in the Orito field. After investigating drilling records they decided on a bit program to drill the well with roller cone bits. However, United Diamond designed a bit program to drill this field with PDC drill bits. After showing Petrobank that these similar lithologies have been drilled using PDC bits elsewhere in the world, the operator decided to run the bit program as put forth by United Diamond.

The well was spudded with a 121/4-in., five-bladed, UD519 PDC bit, which drilled from the surface to hole TD at 37 ft/hr (11m/hr). An insert roller cone bit had been the bit of choice in the past and the operator did not think a PDC could drill this section. Not only did it drill the entire section, but it came out re-runable. Another smaller UD519 bit drilled from surface casing drill-out to core point at 47 ft/hr (14 m/hr), much faster than the 21 ft/hr (6 m/hr) rates achieved with a competitor's seven-bladed bit in the past.

Olympia Energy Inc. in the Harmattan area of west central Alberta, previously had used a PDC and two roller cone bits to drill about 7,550 ft (2,300 m). This section took 147 hours and two trips to drill at an average of 43 ft/hr (13 m/hr). United Diamond went in with its 77/8-in. UD513, five bladed, 1/2-in. cutter PDC and drilled the entire section in 74 hours at a penetration rate of 85 ft/hr (26 m/hr). This saved 73 drilling hours and two round trips.

Hammers for horizontal drilling

Numa, a bit designer and manufacturer based in Thompson, Conn., has a new Patriot rock drilling hammer line and an Impact Ring Bit System that have significantly simplified horizontal drilling for contractors all across the globe.

Recently introduced, the revolutionary Patriot downhole hammer provides unmatched penetration and durability for drilling in hard rock formations (Figure 5). Its simplified design enables tremendous penetration rates with exceptional hammer life throughout the entire product range
(31/2-in. to 48 in.)

The Impact Ring Bit System is a technically advanced, efficient means of drilling in both horizontal and vertical applications that require simultaneous drilling and casing. The system consists of a unique two-piece design incorporating a center and ring bit combination. Upon completion of drilling, the center bit and drill string can be pulled back out of the hole to be used on other projects while leaving the casing installed. This provides the added benefit of lower equipment costs because the product can be reused on multiple projects.

The Impact Ring Bit System enables contractors to drill quickly and accurately. Penetration rates in granite have yielded speeds in excess of 4 in./min (102 mm/min) while accurately drilling on-line and on-grade. The thickness of the ring bit also helps to promote longer and deeper bores. All of these combine to provide the drilling industry with the fastest means available on the market today for setting casing in difficult ground conditions.

Impact Ring Bit Systems are available for both steel and concrete pipes and casing, so the system is also suited for horizontal applications such as piles, pipelines, tie-backs, tunneling under roads and buildings or any other casing installation project.

Gladiator a winner in South America

RBI-Gearhart was the first company to supply a 36-in. rock bit with a sealed roller-bearing. The engineers and manufacturing technologists at RBI-Gearhart only took 10 weeks to create this monster from the drawings, including preparation of molds, dies and specialized fixtures needed using state-of-the-art CAD tools and 3-D solid parametric modeling systems. The king-size SS1 LRGSPJ Gladiator has racked up a number of winning bouts in South America, eliminating the need for multiple pass bit runs with hole openers.

Petrobras utilized the first 36-in. Gladiator bit in the Sabalo-X4 well, located in Southern Bolivia. In a previous offset well it took two competitors' bits and more than 123 hours to drill 79 m, and Petrobras still needed another 36-in. re-run bit to ream to 36 in.

"In our past experience in the San Alberto and Sabalo fields, a total of eight wells, we only had one option to drill a 36-in. hole, and this option was a conventional bit," said Jorge E. Paz Velasco, drilling coordinator superintendent for Petrobras Bolivia. "When RBI-Gearhart presented their newly designed 36-in. Gladiator with sealed bearings, highly protected gauge and proprietary hard metal technology, we knew that we could improve our drilling performance in these two fields. The performance of RBI-Gearhart's 36-in. Gladiator bit was excellent."

The new bit drilled 65 m in 35 hours, completing the section in a single run, saving the Petrobras Bolivia team $80,000 (Figure 6). The Gladiator replaced two 36-in. bit (IADC 1-1-1) runs and came out graded 1/1/NO/A/E/I/NO/TD. It could still be run and had considerable bearing life left.

"In the previous offset well, the ROP was 0.66 m/h. In this current well, SBL-S4, the 36-in. Gladiator ran 1.87 m/h - that is three times faster than the offset well," said Sergio Rabczuk, Codesin sales manager, representative in Bolivia for RBI-Gearhart. "One of the reasons for this performance is the six-point stabilization, which is strongly protected with tungsten carbide inserts."

Comments