The goal of this project is to develop a downhole, high-temperature turbine generator (HTTG) capable of operating at high pressures (>20,000 psi) and high temperatures (250°C) for powering rotary steerable tools; measurement-while-drilling and logging-while-drilling (MWD and LWD) tools and other drill string components, either commercially available or under development.
Dexter Magnetic Technologies, Inc., Elk Grove Village, IL 60007
As oil & gas drilling has become more sophisticated, advanced downhole tools have been developed that require electrical power to operate. Some early tools used conventional lithium ion batteries; those with higher power requirements relied on a wireline run from the surface to the tool that was used both for power and communication. Because it made drilling operations more complicated, developers looked for ways to remove the wireline link. As a result, battery technology was adopted and has become more technologically advanced. Downhole generators were also developed, but have remained more expensive and prone to failure than lithium ion batteries.
Today, the primary electrical power source for LWD, MWD, and other downhole electronics is lithium ion battery (LIB) packs. LIB technology has progressed to provide reliable downhole power at temperatures up to 175°C. However, LIBs have temperature limitations and a number of other characteristics that make them less desirable. In particular, LIBs are costly, have limited recharge cycles (must be disposed of when drained), exhibit a very steep fall-off at the end of their life, and pose a possible explosion and fire hazard.
As an alternative to battery power, downhole generators have been developed by some major downhole service companies for their own use with varying degrees of success. These generators are driven either by turbines powered by the drilling fluid, or by mud motors. None of the commercially available generator systems developed by major service companies are capable of operation at 250°C. To date, there is no existing commercial technology capable of providing downhole power that meets the requirements for operation in deeper, hotter wells.
The advanced HTTG will significantly impact the cost of recovering gas from deep, hot wells. Current state-of-the-art LIBs are not suitable for hotter environments and if modified for elevated temperatures would still be costly and not reusable. A turbine generator will provide reduced dollar-per-amp-hour costs, an important benefit for reducing drilling costs and making deep reservoirs commercially viable. Without a suitable HTTG, it will be impossible to employ “intelligent” drilling tools in high-pressure, high-temperature (HPHT) wells, effectively limiting and delaying the economic development of domestic deep gas reservoirs.
The project began in late 2005. The initial Phase I review identified generator components that needed to be upgraded (mechanical pressure vessels, thread standardization, and O-Rings).
Phase IIA activities began in early 2008. The initial design of a hybrid passive and active generator could not accommodate the package size necessary to fit into the current tool design. The information gathered from this design lead to the current permanent magnet design. The stator portion of the permanent magnet generator prototype was twice the length of the first prototype and therefore produced twice the voltage at a set RPM range. The rotor portion of the permanent magnet generator prototype was converted to a "quadrature" magnetic field design. This permitted a greater amount of magnetic flux to penetrate the copper windings, increasing efficiency.
Flow testing has been conducted on the HPHT turbine generator to evaluate component deterioration due to sharp sand impact and has shown promising results. The tool was required to last one “bit trip” (considered to be 200 hours for most drilling applications). Components experiencing the most amount of wear were the turbine blades and the two devices used to direct the flow of drilling fluid. Upon inspection, all system components were found to be acceptable after 200 hours of use in 1.5% sharp sand by weight.
Phase IIA—development of an HPHT turbine generator prototype for reliable operation in deep downhole environments—is nearly complete. Two prototypes have been manufactured. Preliminary testing has been conducted on both prototypes to confirm that the permanent magnet generators functioned as intended. Both prototypes’ RPM vs. Power curves matched the latest design criteria.
The rectification and regulation circuit needed to convert AC voltage to DC voltage—while maintaining a steady 24 VDC output—was adjusted to reduce power loss during regulation. The current circuit has a less than ideal output after conditioning. This modification was completed in February 2010.
Phase II was completed by the end of April 2010 and was successful in meeting the stated tasks of:
The field testing of the turbine generator prototypes is vital so that a post test evaluation can be conducted to identify any necessary modifications required prior to turbine generator production. Due to the unsuccessful efforts of locating a well site suitable for testing the generator in an HPHT environment, as would be experienced during deep well drilling, Dexter Magnetic Technologies has decided to terminate the project prematurely after Phase II efforts and not to continue to Phase III of the project. Phase III, if the project had continued, was to focus on the field testing of the turbine generator in HPHT conditions to verify that all tool specifications have been met. Currently, the tool has not been exposed to 250°C and 20,000 PSI simultaneously because the testing apparatus needed to accommodate these requirements would be too costly and potentially dangerous. Shock and vibration specifications are also important design criteria that cannot be readily tested outside of a well drilling site.
Dexter Magnetic Technologies has completed Phase II of the Development of a HPHT Turbine Generator, and was in the process to transition into the final phase, Phase III, which would entail field testing of the two HPHT Turbine Generator prototypes developed during Phase II, when the decision arose from Dexter Magnetic Technologies to decline requesting a Phase III transition. The project activities will terminate with the following accomplishments made through the duration of the project:
The final project report is available below under "Additional Information".