The objective of the proposed effort will be to develop a fiber-optic sensing system capable of real-time simultaneous distributed measurement of multiple subsurface, drilling, and production parameters. A proven and breakthrough technology that enables the harmonic-free interrogation of thousands of grating-based distributed interferometers along an optical fiber will be leveraged for long distance, distributed acoustic measurements, and integrated with a novel optical sensing fiber to obtain distributed subsurface electromagnetic field measurements. A novel multi-material, measurand-specific, optical fiber will be fabricated and integrated with the sensing system to enable the distributed and real-time measurement of multiple parameters simultaneously with ultrahigh sensitivity, high frequency, and reliability at depths and temperatures beyond that of current monitoring technologies.

Virginia Polytechnic Institute and University, Blacksburg, VA 24061

Collaborators
Sentek Instrument LLC., Blacksburg, VA 24060

It has been estimated that the recovery efficiencies are on the order of 20% in gas-rich shale reservoirs and less than 10% in liquid-rich plays. Critical knowledge gaps in the understanding of subsurface hydraulic fracture geometry and optimal completion/stimulation strategies continue to limit the most efficient recovery of Unconventional Oil and Gas (UOG) resources. Limitations of currently available technologies to characterize and monitor relavant subsurface features present a major obstacle to understanding the in situ nature of hydrocarbon occurrence and the resultant flow properties of the stimulated reservoir as well as controlling the stimulation and production.

Next-generation logging tools that can image radially from the borehole with high resolution, seismic sensor arrays to monitor stress near the wellbore, and methods to remotely characterize fluid flow are actively sought to assure efficient production. Although several schemes (such as wireless data telemetry, electronics-based technologies, and fiber optic sensors) have been investigated, insufficient performance has limited their widespread efficacy in UOGs. Furthermore, the use of more than one of these technologies to obtain the necessary information further complicates the deployment and is often not feasible because of the stark difference in operating principles and integration procedures. There is a clear need for innovative and breakthrough technologies for improved subsurface characterization, visualization, and diagnostics to fill data gaps in big data analytics to inform decision making and improve ultimate recovery of UOG plays.

The project will demonstrate a ground-breaking technology to view the subsurface with unprecedented clarity, enable real-time facture diagnostics, and optimize drilling and production via the rapid, distributed, and simultaneous measurement of subterranean seismic and electromagnetic phenomena. A one-of-a-kind distributed fiber optic acoustic sensing system will be coupled with a transcendent magnetic fiber optic sensing fiber that will provide seismic and electromagnetic measurements with contrast, spatial resolution, and functionality not yet realized by other techniques. It is envisioned that the simple, minimally invasive, compact, and cost-effective approach will aid in the ultimate recovery from UOG resources and optimal use of the Nation’s subsurface resources, particularly for the small profit margins and fast turnaround time required for decision-making at these sites.

• The performance of the prototype magnetic sensing was optimized to demonstrate higher spatial resolution (2 meter) and enhanced sensitivity (< 0.5 mT) to magnetic fields; a sensing fiber with 2 Metglas® cladding wires was fully integrated with the optimized interrogation system and tested in an air-core solenoid to meet the Succes Criteria for Milestone 7.
• Fabricated an 80 micron sensing fiber with nano-sized (10-1000 nm) nickel cladding wires.
• A 2- meter long magnetic field generating loop was constructed to evaluate the response of sensing fiber upon exposure to transverse magnetic fields and magnetic annealing (~ 400°C); demonstrated an order of magnitude improvement in response of sensing fiber after magnetic annealing at an elevated temperature.
• Demonstrated minimum magnetic field sensitivity on the order of 1 nT with the Sentek acoustic sensing fiber in contact with a Metglas® ribbon.
• Successfully fusion spliced a magnetic sensing fiber with nanosized (10-1000 nm) cladding wires to a standard commercial single mode fiber.
• Refined the data processing techniques to better evaluate the relationship between magnetic field strength and the intensity of the primary FFT peak and associated harmonics.
• A sensing algorithm was developed to quantify and perform an FFT of the beat pattern upon testing under varied magnetic fields for sensor calibration.
• Evaluated the perceived changes in the polarization state of the multi-material sensing upon exposure to magnetic fields of varying strength.
• Sensor biasing was performed by applying a static magnetic field to the sensing fiber to shift the frequency reponse to the AC magnetic field driving frequency.
• Fabricated and characterized sensing fibers with nickel, Galfenol, Permalloy 80, cobalt and copper cladding wires, as well as air holes.
• Fabricated and characterized sensing fibers with three different concentrations of nano-nickel cladding wires.
• Sensing fiber with two nickel cladding wires was shown to be sensitive to EM radiation/electric fields.
• Refined techniques to separate acoustic and magnetic field response of the sensing fibers  and the numerical aperture of a prototype single mode sensing fiber was determined via optical characterization.
• Fabricated additional magnetic sensors and evaluated the response of nickel and Metglas® based magnetic sensing fibers upon exposure to transverse and lateral magnetic fields.
• Demonstrated the capability to perform distributed magnetic sensing by performing measurements at two distinct locations along one fiber strand.
• The response of nickel and Metglas® based magnetic sensing fibers was characterized upon exposure to magnetic fields up to 2.4 mT.
• Separation of multi-component data was successfully demonstrated via three different techniques: fast independent component analysis (FICA), principal component analysis (PCA), and reconstruction independent component analysis (RICA).
• The magnetic sensor test facilities were upgraded with NIST certified magnetic sensors, new air core solenoid, programmable AC power source, high current amplifier and a transverse magnetic field generator
• Protoype magnetic sensing fibers with nickel and Metglas cladding wires were tested in an air-core solenoid to demonstrate a response to AC magnetic field strengths on the order of a microTesla (µT).
• Successfully evaluated the response of the magnetic sensing fiber upon the exposure to a magnetic and acoustic field, simultaneously. 
• Full scale integration of the magnetic sensing fiber with the picoDAS system was successfully demonstrated for evaluating performance upon exposure to magnetic and acoustic fields.
• Sensors with 2 meter spatial resolution were successfully fabricated in a polyimide coated single mode pure silica core optical fiber via femtosecond laser inscription; met Success Criteria for Milestone 6.
• Sensors with 2 meter spatial resolution were successfully fabricated in an array of single mode fibers with nickel and Metglas wires in the cladding.
• Continuous lengths, up to 1 km, of multi-material sensing fibers were successfully fabricated with a strength up to 200 kpsi; met/exceeded Success Criteria for Milestone 4.
•  A single mode core rod was acquired from a commercial vendor that will simplify the manufacturing process and improve performance; a magnetic sensing fiber was successfully fabricated using a length of the single mode core rod.
• DASNova™ sensor interrogator signal processing algorithm was further optimized to allow quasi-static strain or temperature measurement
• Sentek systematically tested the Sentek DAS systems to demonstrate spatial resolutions of 2 m and 5 m and a measurement resolution of 0.2 nε as defined by 3σ; met Success Criteria for Milestone 6.
• Testing was performed to demonstrate DAS systems with 2m and 5m resolution using  acrylate coated sensing fiber, 900 μm hytrel jacketed sensing fiber and 4 mm diameter outdoor rated fiber sensing cable via the recommendation provided in SEAFOM Measuring Sensor Performance Document – 02 (SEAFOM MSP-02); a uniform sensitivity, ± 25%, was also demonstrated along the entire cable lengths tested with a cross-sensitivity free response with noise floors ≤2pε/Hz1/2.
• Successfully fabricated fiber Bragg grating (FBG) sensors in a single mode multi-material fiber with 2 nickle cladding wires via femtosecond laser inscription.
• Sensing fibers characterized via spectral analysis and optical time domain reflectometry (OTDR) exhibited relatively low attenuation (~10 dB/km) at 1550 nm.
• Multi-material sensing fiber with continous lengths up to 600 meters and a tensile strength >50 kpsi were fabricated with 2 and 3 nickel and Metglas™ cladding wires.
• Prototype software was developed to read, visualize, analyze spectra of, and separate simultaneous sources recorded in high-frequency DASNova™ sensing cable data.
• Successfully deployed a DASNova™ sensing cable in an environmental test bed (60 meter trench) and evaluated the response upon exposure to 20 unique acoustic sources.
•  A soil test bed with a 2 meter length was commissioned with capabilities for exposure of the sensing fiber to controlled magnetic fields up to 10 mT, temperatures up to 150ºC, and acoustic fields of varied frequencies.
• A soil test bed with a 5-meter length was constructed to enable testing of sensing fibers with longer sensor gauge lengths.
• Theoretical modeling demonstrated the ability of the sensing fiber with Ni and Metglas® cladding wires to sense magnetic fields much lower than 1 mT.
• Preparations were made to address the large-scale fiber optic data analysis needs that are anticipated in unconventional reservoirs and software was developed to automatically remove anthropogenically-generated seismic noise.
• Sentek successfully constructed DASNova™ interrogators with 2 and 5 meter spatial resolution that will be used to evaluate the response of the sensing fiber samples. 
• Sentek developed and demonstrated a Rayleigh backscatter based DAS system that does not require the inscription of FBG sensors in the fiber.
• Theoretical modeling was performed to evaluate the magnetostriction induced strain distribution characteristics in sensing fiber designs with varied magnetostrictive wire spacing, number and size. The high quality magnetostrictive models were refined with a 1e-9 geometric tolerance, new bottom-up meshing techniques, and benchmarked material property additions.

Activities planned for the coming months include the characterization of the reduced diameter (~80 micron) optical fiber, evaluation of the response of the magnetic sensing fiber to transverse magnetic fields, and characterization of the EM radiation/electric field response of the magnetic sensing fibers. In the next 12 months, the primary goal is to secure funding for field trial testing (3-year program) of the sensing system in a representative downhole environment. To meet this goal, theoretical analyses of prospective applications will be performed, the work will be published in peer reviewed journals, and potential government funding agencies will be engaged. As time and funding permits, a magnetic sensing fiber with high concentrations of Metglas nanowires (<100 nm) will be fabricated and the minimum detectable magnetic field strength will be determined. The data analysis techniques will also be further refined to enhance the results of the magnetic sensing fiber calibration.

$1,500,000
 

$375,000
 

NETL – Gary Covatch (gary.covatch@netl.doe.gov or 304-285-4589)
Virginia Polytechnic Institute and University – Gary Pickrell (pickrell@vt.edu or 540-231-3504)