Advanced Drilling Technologies Research Initiatives

• Development of a Mud Jet-Augmented PDC Bit for Use with Conventional Rig Pressures
• Systems Analysis of Alternative Wellbore Lining Methods
• Development of New Brazing Processes for Attachment of TSP Diamonds to Drag Bits
• Improvement of PDC Drill Bits Incorporating Novel Processing of Cemented WC and Diamond Composites
• Advanced Geothermal Turbodrill
• Binderless Nanophase Cutter Materials for High Rate Hard Rock Drilling
• High Performance Mini-disc Bit with Water-Jet Flushing

The ultimate goal of this advanced drilling program is to reduce geothermal drilling costs by 50 percent or more, though that clearly will not be achieved in a single step or in a narrowly defined effort. The NADET Research Initiatives are intended to be the opening round in a multifaceted, multi-industry, and sustained effort that, with additional funding from a wide variety of sources, can achieve this ambitious goal for a wide range of drilling activities.

The NADET Institute is pleased to announce the initiation of seven advanced drilling research projects as a result of this solicitation. The following abstracts have been prepared by the selected proposers to briefly describe the projects. Though selected for their relevance to advanced geothermal drilling, the source of the available funds, all of the projects are clearly relevant to a much wider range of drilling and excavation activities, as is the NADET intent.

For purposes of the RFP, geothermal drilling was distinguished from typical oil and gas drilling by harder rock or interbedded hard and soft rock, higher temperatures, more frequent and more serious lost circulation, increased corrosion and erosion of components, larger hole diameters, and remote, inaccessible drill sites. The RFP solicited innovative, even revolutionary, ideas with the potential to achieve substantial cost reductions.

Because the solicitation sought the best new ideas for advanced drilling, rather than preconceived solutions to a narrowly defined program, the proposal process began with asking for five page preliminary proposals. Sixty-one preliminary proposals were received in response to this request. The range of concepts was encouraging, from laser beam excavation to improvements for today's "conventional" practices. The most common concepts proposed related to bit design (i.e., mechanical excavation bits) and to advanced (generally diamond) materials for drag bit designs. Others included some systems and system component studies and basic rock mechanics research.

Proposals were evaluated by a committee of nine highly qualified reviewers. Sixteen full proposals were invited from the sixty-one candidates. Full proposals were limited to ten pages of text. Fifteen full proposals were received (two of the sixteen were combined as had been recommended by the evaluation committee). These were reviewed by the same group, and the seven described here were selected for funding.

The evaluation committee was made up of six industry representatives, two academics, and one government employee. Backgrounds included producers, drillers, consultants, advanced technology researchers, and drilling equipment designers.

A geothermal industry advisory group formed to provide advice in the preparation of this RFP will continue to offer advice on future NADET Institute programs in the geothermal area. Similar standing advisory committees will be formed for other industries as the NADET program grows.

The following abstracts are presented as received from the contractors:

Development of a Mud Jet-Augmented PDC Bit for Use with Conventional Rig Pressures

This project will develop and demonstrate the effectiveness of a mud jet-augmented PDC bit that drills with improved penetration rates and bit life in hard rock (>20,000 psi compressive strength) using mud pump pressures that are currently available or can be economically installed on the drill rig (<6,000 psi). The proposed mud jet augmentation involves the use of pulsating, cavitating jets directed at the cutter-rock interface near the leading edge of selected cutters on the face of a PDC bit. The bit would take advantage of the synergistic hydraulic-mechanical effects that have repeatedly been shown to result in significant reductions in drag cutter forces in hard rock. Reduced cutter forces result in improved bit life. The goal of this project is to make the primary advantage of PDC bits, which is more efficient and rapid cutting, applicable to hard rock.

Doubling of both bit life and penetration rate over that attainable with roller-cone bits (typically 7-10 ft/hr in hard formations) would reduce geothermal well costs by about 15%, or $300-450k, for a $2-3 million well. Because drilling costs represent about one-half the cost of a geothermal power project, such cost savings would reduce power project costs by about 7.5%. Assuming that total mud jet-augmented PDC bit costs for a given multiple-bit well are $50k more than those for roller-cone bits of the same size, a cost/benefit ratio of about 50/400, or 1/8, is therefore possible.

Under this project, Sandia National Laboratories will assist in the design of the prototype bit, using its PDCWEAR code to optimize placement of the cutters and nozzles; and coordinate joint work activities, including planning and design reviews, laboratory and field testing, and reporting. Security DBS will lead the mechanical design of the bit; fabricate the prototype bit; participate in laboratory and field testing activities; and assist in planning and reporting. Dynaflow, Inc., will conduct design studies and laboratory testing to optimize nozzle performance for this application; design and fabricate nozzles and provide them to Security DBS for incorporation into the prototype bit; and assist in planning and reporting. Terra Tek will conduct laboratory testing of prototype bits under simulated downhole conditions.

Systems Analysis of Alternative Wellbore Lining Methods

This project will examine alternatives to the conventional practice of lining a wellbore with steel pipe, or casing, sealed in place by pumped cement after a relatively long interval of drilling a constant-diameter hole. A system which could line the hole as it is drilled would be extremely cost-effective, for it would solve or mitigate problems caused by lost circulation, stuck pipe, wellbore instability, and faulty cement jobs around conventional steel casing. Many wells would require fewer casing strings and the casing would be of smaller diameter, accruing additional cost savings. These savings would be especially relevant to the geothermal industry because lost circulation is much worse than in hydrocarbon drilling, and the large production rates for geothermal wells usually require larger casing than in oil and gas wells at comparable depth.

There are eight principal tasks in this project:

• Review literature and patents, interview past/present researchers to define the state-of-the-art.
• Define situations or applications in which the wellbore-lining system could be used.
• From the application scenarios, define functions which the wellbore lining system must perform.
• Based on the functional requirements, define two or more conceptual systems, realizing that a particular system may not perform all functions.
• Develop functional and cost criteria for selection of a conceptual design.
• Identify critical system information, distinguishing between currently available data and that which is still needed for the conceptual design.
• Estimate data criticality by sensitivity analysis.
• Develop conceptual layouts of the two most promising systems.
• Document the study with a Final Report which includes drawings or diagrams of the most promising systems, rationale for the selection process, strengths and weaknesses of each system, estimates of development and operational cost for each system, and a Program Plan for continued development.

Development of New Brazing Processes for Attachment of TSP Diamonds to Drag Bits

This proposal addresses the geothermal drilling problems of dealing with harder rock and higher well-bore temperature gradients. TSP (thermally stable polycrystalline) bits are currently made with small TSP diamonds imbedded in a bit matrix body, resulting in a relatively small cutter standoff, and hence, low penetration rates. The objectives of this NADET project are to

1. develop unique, high attachment shear and impact strength TSP diamond cutters which allows greater cutter exposure, as are lower temperature capacity PDC (polycrystalline diamond compact) cutters,
2. design new TSP drag bits, and
3. demonstrate the capability to economically drill hard-rock in laboratory and field testing.

Doubling of both bit life and penetration rate over that of roller cone bits will reduce geothermal well costs by about 15%, or $300 to $450 savings for $2 to $3 million wells. Because drilling costs typically represent 1/2 the cost of a geothermal power project, total project costs could be reduced by about 7.5%. If TSP bit costs for a given multiple-bit well were $50k more than those for roller cone bits, a cost/benefit ratio of about 50/400 or 1/8 is therefore possible.

Phase I and II will develop two new brazing processes, and, if successful, Phase III will include both laboratory and field performance testing of new TSP diamond drag bit designs. Phase I and II will each be performed in 12 months, and Phase III in 36 months. Technology International, Inc., (TII), the Jet Propulsion Laboratory (JPL), the Colorado School of Mines (CSM), and Sandia Laboratories form an interdisciplinary team which is qualified to effectively transfer technology from the laboratory to commercial applications. For more information contact Bob Radtke, Principal Investigator, Technology International, 2103 River Falls Dr., Kingwood, TX 77339-31543, Ph/Fax: (713) 359-8520, email: radtke@onramp.net.

Improvement of PDC Drill Bits Incorporating Novel Processing of Cemented WC and Diamond Composites

An improved PDC drill bit will be designed and produced during the extended multi-year proposal period. Newly developed microwave sintering is the key in preparing nanocomposites of sintered carbide without the need of grain growth inhibitors. Microwave processing has several advantages over conventional sintering, such as the potential for significant reduction in manufacturing costs, improved mechanical properties and hence enhancement in the performance of the product. Composite diamond layers will protect the bit surfaces. PDC structures plus bonding methods with higher temperature and improved wear capabilities will extend the life of the bit in geothermal environments.

Since microwave processing is known to be highly energy efficient due to the fact that it is accomplished by internal heating of the cement powders, the sintering cycle time of cemented carbide has been reduced by an order of magnitude as compared to conventional sintering methods. Thus, we can sinter micron size WC plus Co tooling in a matter of minutes versus hours. For example, 6% Co tungsten carbide was sintered at 1250-1350ºC in 10-30 minutes with a density of 15g/cc and 93 Rockwell A hardness while maintaining the grain size at less than two microns. This would take hours by conventional methods and grain growth inhibitors would be needed. The carbide produced with this method will be used for substrates and wear parts for the PDC's and metal will be applied to a complex bit surface. Modified PDC cutters with diamond wear pads on the supporting carbide substrate will reduce the friction heating due to carbide wearland formation. Less heat generated at the PDC wearland will allow the bit to be used in higher temperature environments. The final innovation that will be applied to the bit development is the high temperature PDC braze which will allow the stress to be reduced in the carbide and the thermal stability of the braze to be increased by as much as 300ºC.

Advanced Geothermal Turbodrill

Maurer Engineering is developing an advanced high-temperature turbodrill for drilling hard rocks at high drilling rates. This turbodrill utilizes 50 sets of turbine blades to convert hydraulic power from the drilling mud to rotary mechanical power to power the drill bit. This advanced turbodrill will be developed by modifying a geothermal turbodrill used in the 1970s in LANL's hot dry rock wells at Fenton Hill, NM. A gear box will be added to the LANL turbodrill to reduce its speed from 1000 to 100 rpm for use with hard rock roller bits. Improved thrust bearings will be used to allow higher bit weights and increase the reliability of the turbodrills. If successful, these advanced turbodrills should increase drilling rates 2-3 fold and allow the drilling of multi-branch geothermal wells that could increase steam production 2-3 fold.

Binderless Nanophase Cutter Materials for High Rate Hard Rock Drilling

The performance of cutter material has a significant economic impact on the drilling process. It is common that a Polycrystalline Diamond (PCD) bit will drill as much as four to five times the depth of a conventional cone bit, reducing not only the cost per meter but also the trip time which can significantly reduce the cost for deep drilling operations with very high rig rates. Geothermal drilling presents the following obstacles to application of the conventional PCD materials:

1. Elevated temperature of the rock leads to a loss of strength of PCD material due to graphitization assisted by the cobalt present in the polycrystalline diamond matrix;
2. The corrosive down hole environment leads to reduction of strength of PCD and WC/co substrates due to etching of Cobalt binder.

Recently developed Binderless Polycrystalline Diamond (BPCD) materials exhibit superior thermal and corrosion stability. This program will explore performance of BPCD types of materials at geothermal drilling conditions. Research will focus on two main aspects:

1. BPCD cutters material performance under conditions encountered during geothermal drilling including bottom-hole high temperature corrosive environment;
2. Feasibility of integration of the BPCD cutters into corrosion and erosion resistant drill bits that will be produced by high temperature sintering methods.

High Performance Mini-disc Bit with Water Jet Flushing

This study and demonstration program involves the use of very small, disc-type cutters, trade named "Mini-discs", applied to popular drill bit sizes. The basic science behind the use of Mini-discs is that they slice the rock, creating tension failures and causing chips to pop off the rock face between the cutter tracks. Average size of the cuttings formed is larger than with conventional hard rock roller cone bits. Specific Energy of Excavation, energy consumed per unit mass of rock excavated, is reduced. For a given amount of power applied, a Mini-disc bit goes faster. In early laboratory tests, a 13 1/8 inch bit penetrated at a rate of 70 ft/hr and a 7 7/8 inch bit at over 130 ft/hr, both in 25,000 psi rock. These rates were achieved at less than optimum rpm and with inadequate drill fluid circulation. This program will focus on drill fluid circulation; pressure, injection points, and a controlled flow path within the bit. The objective is to determine the most favorable injection point, at the lowest hydraulic horsepower which will enhance performance, cuttings removal and at the same time produce adequate bit cooling. The project includes fabrication and laboratory testing of a Mini-disc drill bit. The project has the potential to substantially reduce drilling costs in several ways.

• In laboratory experiments, drilling rates were extremely high. The potential for reduced drill crew time on a hole is very cost effective.
• Bit life, in terms of footage drilled, is likely to increase as a result of the penetration rate increases. With disc cutters, life in hours varies little whether the penetration rate is fast or slow. For example, a very reasonable 50 hours life at 100 ft/hr equals 5,000 feet of hole between trips.
• Bits can be refurbished, in the field, in less than an hour, and at a fraction of the cost of a new bit. This is a particularly valuable feature in serving remote drilling sites.