EP-4735852-A1 - DAS DEPTH CALIBRATION WITH MULTI-GAUGE LENGTH INTERROGATION

Abstract

Systems and methods are presented for determining a calibrated vertical seismic profile (VSP) with a distributed acoustic sensing (DAS) system in a borehole (108). The methods include obtaining a density log and an acoustic slowness log for the borehole (108); determining a first impedance, a DAS impedance from well log (DIL) curve, from the density log and the acoustic slowness log; obtaining a VSP dataset in the borehole (108); for each of the plurality of gauge lengths: determining a second impedance, a DAS from vibrations (DIV) curve, from the VSP dataset for the plurality of gauge lengths, and determining a fit between the DIV curves and the DIL curve by using a misfit functional for each of a plurality of depth adjustments. The method further includes determining the calibrated VSP by applying a preferred depth adjustment to the VSP dataset.

Inventors

• KAZEI, VLADIMIR
• Titov, Aleksei
• BAKULIN, ANDREY

Assignees

• Saudi Arabian Oil Company

Dates

Publication Date

20260506

Application Date

20240621

Claims (1)

1. ATTORNEY DOCKET NO.18733-947WO1; CLIENT REF. NO. SA9947 – ASC0759-US01-NP CLAIMS What is claimed: 1. A method for determining a calibrated vertical seismic profile (VSP) with a distributed acoustic sensing (DAS) system in a borehole (108), comprising: obtaining a density (304) log and an acoustic slowness (302) log for the borehole (108), wherein each log comprises a value recorded at a plurality of locations common to the density (304) log and the acoustic slowness (302) log; determining a first impedance, a DAS impedance from well log (DIL) curve, from the density (304) log and the acoustic slowness (302) log; obtaining a VSP dataset in the borehole (108), wherein the VSP dataset comprises a plurality of acoustic signals generated by a seismic source (116) and recorded with the DAS system for a plurality of gauge lengths; for each of the plurality of gauge lengths: determining a second impedance, a DAS from vibrations (DIV) curve, from the VSP dataset for the plurality of gauge lengths, and determining a fit between the DIV curves and the DIL curve by using a misfit functional for each of a plurality of depth adjustments; and determining the calibrated VSP by applying a preferred depth adjustment to the VSP dataset. 2. The method of claim 1, wherein the misfit functional comprises a plurality of correlation coefficients between the DIV curves and the DIL curve. 3. The method of claim 1 or 2, wherein determining each of the plurality of depth adjustments comprises determining a plurality of depth shifts. 4. The method of any one of claims 1 to 3, wherein selecting the preferred depth adjustment comprises determining the depth adjustment that maximizes the misfit functional. ATTORNEY DOCKET NO.18733-947WO1; CLIENT REF. NO. SA9947 – ASC0759-US01-NP 5. The method of any one of claims 2 to 4, wherein the correlation coefficients comprise a Pearson correlation coefficient. 6. The method of any one of claims 1 to 5, wherein the DAS system comprises a fiber- optic cable (106) coupled to a laser light source and to an optical interrogator (110), wherein the optical interrogator (110) decodes a backscattered laser light from a plurality of locations along the fiber-optic cable (106). 7. The method of claim 6, wherein the gauge length comprises a length of a portion of the fiber-optic cable (106) that determines one of the plurality of acoustic signals. 8. The method of any one of claims 1 to 7, further comprising: forming, using a seismic processing system, a seismic image based, at least in part, on the DAS dataset; and planning, using a well planning system, a sidetrack borehole trajectory based, at least in part, on the seismic image. 9. The method of claim 8, further comprising drilling, using a drilling system, a sidetrack borehole guided by the sidetrack borehole trajectory. 10. A non-transitory computer readable medium storing instructions executable by a computer processor, the instructions comprising functionality for: receiving a density (304) log and an acoustic slowness (302) log for a borehole (108), wherein each log comprises a value recorded at a plurality of locations common to the density (304) log and the acoustic slowness (302) log; determining a first impedance, a DAS impedance from well log (DIL) curve, from the density (302) log and the acoustic slowness (304) log; for each of a plurality of gauge lengths: determining a second impedance, a DAS from vibrations (DIV) curve, from a VSP dataset for the plurality of gauge lengths, and ATTORNEY DOCKET NO.18733-947WO1; CLIENT REF. NO. SA9947 – ASC0759-US01-NP determining a fit between the DIV curves and the DIL curve by using a misfit functional for each of a plurality of depth adjustments; selecting a preferred depth adjustment based, at least in part, on the misfit functional; and determining a calibrated VSP by applying the preferred depth adjustment to the VSP dataset. 11. The non-transitory computer readable medium of claim 10, wherein the misfit functional comprises a plurality of correlation coefficients between the DIV curves and the DIL curve. 12. The non-transitory computer readable medium of claim 10 or 11, wherein determining each of the plurality of depth adjustments comprises a depth shift. 13. The non-transitory computer readable medium of any one of claims 10 to 12, wherein selecting the preferred depth adjustment comprises determining the depth adjustment that maximizes the misfit functional. 14. The non-transitory computer readable medium of any one of claims 10 to 13, further comprising forming, using a seismic processing system, a seismic image based, at least in part, on a DAS dataset. 15. A system, comprising: a logging system, configured to obtain a density log and an acoustic slowness log for a borehole (108); a DAS system, configured to record seismic data from a vertical seismic profiling (VSP) experiment with a seismic source for a plurality of gauge lengths in the borehole (108); a VSP processing system, configured to: determine a first impedance, a DAS impedance from well log (DIL) curve, from the density log and the acoustic slowness log; for each of the plurality of gauge lengths: ATTORNEY DOCKET NO.18733-947WO1; CLIENT REF. NO. SA9947 – ASC0759-US01-NP determine a second impedance, a DAS from vibrations (DIV) curve, from a VSP dataset for the plurality of gauge lengths, and determine a fit between the DIV curves and the DIL curve by using a misfit functional for each of a plurality of depth adjustments; select a preferred depth adjustment based, at least in part, on the misfit functional; determine a calibrated VSP dataset by applying the preferred depth adjustment to the VSP dataset; and a seismic processing system configured to form a seismic image based, at least in part, on the calibrated VSP dataset obtained by the DAS system. 16. The system of claim 15, wherein the DAS system comprises a fiber-optic cable (106) coupled to a laser source and an interrogator (110). 17. The system of claim 16, wherein the interrogator (110) is configured to decode a backscattered laser light from a plurality of locations along the fiber-optic cable (106). 18. The system of claim 16 or 17, wherein the interrogator (110) is configured to use the gauge length to measure a backscattered laser light from portions of the fiber- optic cable (106) to determine a plurality acoustic signals. 19. The system of any one of claims 15 to 18, further comprising a well planning system configured to plan, a sidetrack borehole trajectory based, at least in part, on the seismic image. 20. The system of claim 19, further comprising a drilling system configured to drill a sidetrack borehole guided by the sidetrack borehole trajectory.

Description

ATTORNEY DOCKET NO.18733-947WO1; CLIENT REF. NO. SA9947 – ASC0759-US01-NP DAS DEPTH CALIBRATION WITH MULTI-GAUGE LENGTH INTERROGATION BACKGROUND [0001] Distributed acoustic sensing (DAS) is a method for recording seismic data involving an interrogator device that constantly sends light pulses through a fiber-optic cable and records backscattered signals. The backscattering occurs along the cable and can be analyzed to record a seismic wavefield impinging upon it. [0002] Vertical seismic profiling (VSP) is a useful application of DAS to seismic data acquisition. Depth calibration is essential for VSP with DAS and allows for the localization of observed perturbations in the fiber-optic cable. SUMMARY [0003] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. [0004] In general, in one aspect, embodiments are disclosed related to methods for determining a calibrated vertical seismic profile (VSP) with a distributed acoustic sensing (DAS) system in a borehole. The methods include obtaining a density log and an acoustic slowness log for the borehole, wherein each log comprises a value recorded at a plurality of locations common to the density log and the acoustic slowness log; determining a first impedance, a DAS impedance from well log (DIL) curve, from the density log and the acoustic slowness log; obtaining a VSP dataset in the borehole, wherein the VSP dataset comprises a plurality of acoustic signals generated by a seismic source and recorded with the DAS system for a plurality of gauge lengths; for each of the plurality of gauge lengths: determining a second impedance, a DAS from ATTORNEY DOCKET NO.18733-947WO1; CLIENT REF. NO. SA9947 – ASC0759-US01-NP vibrations (DIV) curve, from the VSP dataset for the plurality of gauge lengths, and determining a fit between the DIV curves and the DIL curve by using a misfit functional for each of a plurality of depth adjustments. The methods further include determining the calibrated VSP by applying a preferred depth adjustment to the VSP dataset. [0005] In general, in one aspect, embodiments are disclosed related to a non- transitory computer-readable medium storing instructions executable by a computer processor, the instructions comprising functionality for the steps of: receiving a density log and an acoustic slowness log for a borehole, wherein each log comprises a value recorded at a plurality of locations common to the density log and the acoustic slowness log; determining a first impedance, a DAS impedance from well log (DIL) curve, from the density log and the acoustic slowness log; for each of a plurality of gauge lengths: determining a second impedance, a DAS from vibrations (DIV) curve, from a VSP dataset for the plurality of gauge lengths, and determining a fit between the DIV curves and the DIL curve by using a misfit functional for each of a plurality of depth adjustments. The steps further include selecting a preferred depth adjustment based, at least in part, on the misfit functional; and determining a calibrated VSP by applying the preferred depth adjustment to the VSP dataset. [0006] In general, in one aspect, embodiments are disclosed related to systems comprising a logging system, configured to obtain a density log and an acoustic slowness log for a borehole; a DAS system, configured to record seismic data from a vertical seismic profiling (VSP) experiment with a seismic source for a plurality of gauge lengths in the borehole; and a VSP processing system, configured to determine a first impedance, a DAS impedance from well log (DIL) curve, from the density log and the acoustic slowness log and, for each of the plurality of gauge lengths, to determine a second impedance, a DAS from vibrations (DIV) curve, from a VSP dataset for the plurality of gauge lengths, and determine a fit between the DIV curves and the DIL curve by using a misfit ATTORNEY DOCKET NO.18733-947WO1; CLIENT REF. NO. SA9947 – ASC0759-US01-NP functional for each of a plurality of depth adjustments. The VSP processing system is further configured to select a preferred depth adjustment based, at least in part, on the misfit functional, and determine a calibrated VSP dataset by applying the preferred depth adjustment to the VSP dataset. The systems further include a seismic processing system configured to form a seismic image based, at least in part, on the calibrated VSP dataset obtained by the DAS system. [0007] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims. BRIEF DESCRIPTION OF DRAWINGS [0008] Specific embodiments of the disclosed technology will now be described in detail with reference to the accompanying figures. Like elements in the v