# US 12,601,253 B2 · Topside interrogation using multiple lasers for distributed acoustic sensing of subsea wells > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,601,253 B2 - Document ID: US12601253B2 - Status: Granted - Kind: B2 - Application number: 18/367,694 - Filed: 2023-09-13 - Published: 2024-01-04 - Granted: 2026-04-14 - Earliest claimed: 2020-11-11 - Assignees: Halliburton Energy Services, Inc. - Applicants: Halliburton Energy Services, Inc. - Inventors: Andreas Ellmauthaler; John Laureto Maida, Jr.; Glenn Andrew Wilson - Web page: https://patentgrep.com/patent/US12601253B2 ## CPC - E21B 47/135: using light waves, e.g. infrared or ultraviolet waves - E21B 47/001: for underwater installation - E21B 47/0025: {generating an image of the borehole wall using down-hole measurements, e.g. acoustic or electric} - E21B 47/07: Temperature - E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS ## Abstract A distributed acoustic system (DAS) may include an interrogator that includes two or more lasers, a pulser module disposed after and connected to each of the two or more lasers, a wavelength division multiplexer (WDM), wherein each of the pulser modules are connected to the WDM as inputs, and a downhole fiber attached to the WDM as an output and wherein the downhole fiber includes at least one sensing fiber. A method for increasing a sampling frequency may include identifying a length of a downhole fiber connected to an interrogator, generating and launching a light pulse from each of the two or more lasers the pulser module, and delaying an output from the pulser module into the downhole fiber by k N seconds, where k is a pulse repetition interval of the pulser module and N is equal to the two or more lasers. ## Claims ### Claim 1 A method comprising: generating and launching one or more light pulses of a first optical frequency from at least one laser into a fiber optic cable, wherein the light pulses traverse the fiber optic cable to a sensing fiber; forming a backscatter signature based on at least two combinations of the light pulses in the sensing fiber, wherein the backscatter signature traverses from the sensing fiber to a photodetector assembly; determining one or more phases of the backscatter signature, wherein determining the one or more phases comprises: shifting the first optical frequency to a second optical frequency with an acousto-optic modulator; taking one or more measurements of the backscatter signature and the second optical frequency; and comparing the one or more measurements with an information handling system to find a heterodyne beat signal, determining a seismic energy of the backscatter signature based at least in part on the one or more phases; and identifying a strain along the fiber optic cable based at least in part on the seismic energy of the backscatter signature. ### Claim 2 (depends on 1) The method of claim 1, further comprising amplifying the light pulse with an Erbium doped fiber amplifier (EDFA). ### Claim 3 (depends on 2) The method of claim 2, wherein the EDFA is disposed between the at least one laser and the fiber optic cable. ### Claim 4 (depends on 1) The method of claim 1, wherein the acousto-optic modulator is disposed in an interferometer. ### Claim 5 (depends on 1) The method of claim 1, further comprising detecting the backscatter signal and the second optical frequency with the photodetector assembly. ### Claim 6 (depends on 5) The method of claim 5, wherein the information handling system is connected to the photodetector assembly. ### Claim 7 (depends on 1) The method of claim 1, further comprising identifying one or more regions of the fiber optic cable for which backscatter is received with the information handling system. ### Claim 8 (depends on 1) The metho of claim 1, further comprising amplifying the backscatter signal with an Erbium doped fiber amplifier (EDFA). ### Claim 9 (depends on 8) The method of claim 8, wherein the EDFA is disposed between the sensing fiber and the information handling system. ### Claim 10 (depends on 1) The method of claim 1, further comprising multiplexing the light pulse with a wavelength division multiplexer (WDM) as the light pulse traverses through the fiber optic cable. ### Claim 11 A distributed acoustic system (DAS) comprising: two or more lasers; a wavelength division multiplexer (WDM) disposed after and connected to each of the two or more lasers; one or more pulser modules directly connected to the WDM as inputs, wherein each pulser module is configured to launch two or more combinations of the light pulses; a distal circulator connected to the pulser module by a fiber optic cable; a downhole fiber attached to the distal circulator as an output and wherein the downhole fiber comprises at least one sensing fiber, wherein a backscatter signature associated with the two or more combinations of light pulses traverses the at least one sensing fiber; and a parse device configured to separate the backscatter signature into one or more phase components for calculation of a seismic energy of the backscatter signature, wherein the calculated seismic energy is indicative of a strain along the at least one sensing fiber. ### Claim 12 (depends on 11) The DAS of claim 11, further comprising an Erbium doped fiber amplifier (EDFA) disposed between the pulser module and the distal circulator. ### Claim 13 (depends on 11) The DAS of claim 11, wherein the pulser module delays a light pulse for each of the two or more lasers into the downhole fiber by k N seconds, where k is a pulse repetition interval of the pulser module and N is equal to a number of lasers that are at least a part of an interrogator. ### Claim 14 (depends on 11) The DAS of claim 11, further comprising a photo detector assembly connected to the distal circulator by a second fiber optic cable. ### Claim 15 (depends on 14) The DAS of claim 14, further comprising a second EDFA disposed between the distal circulator and the photo detector assembly. ### Claim 16 (depends on 15) The DAS of claim 15, further comprising an interferometer disposed between the second EDFA and the photo detector assembly. ### Claim 17 (depends on 16) The DAS of claim 16, further comprising a second WDM disposed between the second EDFA and the photo detector assembly. ### Claim 18 (depends on 17) The DAS of claim 17, further comprising the interferometer disposed between the second EDFA and the second WDM. ### Claim 19 (depends on 18) The DAS of claim 18, further comprising two or more parse devices disposed between the second WDM and the photo detector assembly. ### Claim 20 (depends on 19) The DAS of claim 19, further comprising an information handling system connected to the photo detector assembly.