|Fabry-Perot MEMS Accelerometers for Advanced Seismic Imaging
||Last Reviewed 12/30/2013
The objective of this project is to build and demonstrate the Lumedyne Technologies, Inc. accelerometer technology for microhole seismic imaging.
Lumedyne Technologies Incorporated San Diego, CA 92123
Lawrence Berkeley National Laboratories
Energy needs in the U.S. and worldwide continue to grow. Estimates by the U.S. Department of Energy (DOE) and energy producing companies project an up to 60 percent increase in energy demand over the next 25 years. Domestic oil and natural gas recovery will play an important role in meeting our nation’s energy and economic security goals during that period. Enhanced oil recovery (EOR) and natural gas from tight and unconventional resources are primary targets for U.S. energy production.
In a series of reports for the DOE, Advanced Resources International suggests that domestic hydrocarbon production rates could increase several-fold with the widespread application of state-of-the-art seismic technology to image oil and gas reservoirs. Great strides have been made in processing data to obtain sharper images, but higher resolution and real-time imaging are needed for accurate reservoir modeling. Two heavily used technologies—high resolution 3-D seismic and vertical seismic profiling (VSP)—require that sensors be placed on the surface or in shallow holes (a few inches to a few feet deep) to record signals generated by seismic sources and image the subsurface. A key to obtaining high resolution data is adequate band width and signal-to-noise ratio, which requires that the sensors be placed over large areas (tens of square miles), or by placing them in boreholes.
In addition to active measurements, “passive seismic” monitoring of micro earthquake activity induced by fluid movement and stress changes in the subsurface can be monitored given the proper signal-to-noise ratio. Seismic technology has relied on decades-old geophones. Alternatives like micro-electro-mechanical systems (MEMS) and fiber optic sensors show promise, but neither has had the bandwidth or sensitivity to replace conventional geophones. With further research and development, as is currently being undertaken by this project,these technologies can lead to systems that offer lower unit cost, higher bandwidth, and better noise levels in smaller packages that can easily be deployed on the surface or in boreholes. This approach reduces survey costs, enables “permanent” installations (due to low cost and ease of installation), and provides better data for high resolution subsurface imaging.
Recent DOE-funded research suggests a "designer seismic" approach is the solution, i.e., drilling a number of strategically placed, small diameter, inexpensive microholes and permanently installing small receivers for high resolution, relatively inexpensive seismic monitoring. The need for this technology will increase as the energy industry moves toward increased reliance on enhanced oil recovery and regulatory agencies begin to require CO2 sequestration to combat global warming. One key requirement for successful CO2 sequestration is long-term monitoring of CO2 movement; if seismic sensors could be inexpensively placed in the subsurface, an order of magnitude increase in monitoring capability may be possible. To achieve this objective, inexpensive drilling technology must be combined with ease of sensor installation.
Ultimately, sensors would be installed on the drill pipe and wired in with the drilling tools so that the well can be drilled and all equipment cemented in place without physically having to remove and re-insert the drill string. This “one pass” installation would save time, reduce potential well problems, and reduce the risk of having to re-drill the wellbore. In an effort funded by the DOE, Lawrence Berkeley National Laboratories (LBNL) and its partners are developing a coil tube drilling technology to install sensors in the subsurface at dramatically lower costs (25–50 percent) with reduced environmental impact through faster drilling time and a smaller footprint. Instrumentation of these microholes continued to be a challenge because this new technology reduced the borehole diameter from 4 inches to approximately 1 inch. Packaging and emplacement of geophones at this reduced diameter is problematic and current MEMS accelerometers do not provide the required signal-to-noise ratio. Lumedyne’s new optical MEMS accelerometer enables this new microhole drilling technique by offering an acceptable signal-to-noise ratio in a smaller package that can benefit both traditional land and seabed seismic imaging.
There is a great need for low cost, high-sensitivity, wide bandwidth sensors that can provide higher resolution spatial and temporal imaging results. It is currently too expensive to deploy large numbers of sensors for more than a few weeks, yet there is a need for “permanent monitoring” to “watch” critical reservoir processes develop and change through time-lapse imaging. Applications could include real-time monitoring of hydrofractures; reservoir production management (both active and passive monitoring) at resolutions of less than a few meters; fine-scale imaging of potential and existing reservoirs, and much improved imaging in general. If successful, this new MEMS technology will reduce the cost of deploying seismic instrumentation to the point that surface and borehole surveys will become routine and the vision of a truly “instrumented” oil field /gas reservoir will become a reality. This technology is meant to provide the seismic exploration and monitoring industry with a much needed “leap” rather than a small, incremental step in performance.
- LTI fabricated new accelerometer components, but they noted during testing that there are still inconsistencies in their manufacturing process. They have made a technology breakthrough that could lead to a more simplified manufacturing process along with equal to better hardware performance.
- Successful demonstration of the ability to eliminate the resistive heater from the design
- Successful demonstration of proof mass loop closure
- Successful proof mass actuation demonstrated with the new, redesigned electronics
- The Custom Vertical-Cavity Surface-Emitting Laser (VCSEL) light source has been replaced by an RCLED. This resolves both the secondary cavity issues and the VCSEL signal-noise-ratio.
- LTI tested the fabricated system and observed an issue with the manufactured component functionality. They determined that the fabricated system did not meet the required specifications/tolerance and will have to be re-manufactured.
- Accelerometer design, simulation, and fabrication have been completed.
- Completion of system level analysis
- Package Design complete
- Fabrication of the MEMS die is complete.
- MEMS fabrication complete
- Proof Mass Loop Closure Electronics complete
- Improved Cap Wafer design is complete.
- Heater Loop Closure Electronics complete
- VCSEL Loop Closure Electronics complete
- VCSEL completed
- Resistive Heater Fabrication & Evaluation completed
- Determination of target sensor specifications
- Prototype electronics completed
- Temperature compensating resistive heater fabricated
- Model verification on fabricated components
- High-level electronics design and analysis complete
- Completed MEMS sensor design and modeling.
- Accelerometer design and simulation complete
- Prototype accelerometers were successfully fabricated
- Successful electronic actuation of the proof mass with the newly redesigned electronics has been accomplished. This is a critical step in the integration of the electronics with the MEMS device and shows that the electronics are capable of providing the appropriate force feedback voltage to close the loop around the proof mass.
- The loop closure electronics have been successfully integrated with an accelerometer.
- Researchers have successfully completed component-level optimization bench tests of the accelerometer technology.
- Researchers have successfully transitioned from DC to AC actuation voltage, providing performance enhancement to the accelerometer.
Current Status (December 2013)
Lumedyne has made a technology breakthrough that could lead to a better accelerometer. The benefits of the breakthrough would include improved low frequency response, lower power consumption, lower unit cost, and longer product life. LTI has requested a 12 month no-cost time extension to the award to implement the new breakthrough into the accelerometer. NETL is reviewing the request and a decision is forthcoming.
Project Start: October 1, 2008
Project End: January 31, 2014
DOE Contribution: $1,256,277
Performer Contribution: $513,704
NETL – William Fincham (email@example.com or 304-285-4268)
Lumedyne Technologies Incorporated – Brad Chisum (firstname.lastname@example.org or 619-602-5414)
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