Abstract: A method may include providing a sensor in a first wellbore segment, providing a sensor in a second wellbore segment, observing upgoing acoustic waves or downgoing acoustic waves with the sensors, and separating the upgoing acoustic waves and/or the downgoing acoustic waves from a total wavefield. The first wellbore segment and the second wellbore segment may be separated by a distance. At least one of the wellbore segments may be non-vertical and/or the first wellbore segment may not be parallel to the second wellbore segment. The first wellbore segment may be part of a first set of wellbores and the second wellbore segment may be part of a second set of wellbores. The separated upgoing and downgoing acoustic waves may be used to generate deghosted data.

Abstract: A seismic source (50) is buried in a multi-layered subsurface formation below a fast layer (30) and above a reflecting interface (10). The seismic source (50) excites a critically refracted (CR) wave that travels laterally along a fast layer bottom interface (35), and emanates downwardly into a slow layer (40) that is below and adjacent to the fast layer (30). One or more receivers (60), positioned below the fast layer (30) and above the reflecting interface (10) are used to detect seismic waves (84, 86). The one or more receivers (60) are positioned within a borehole (65). At least one reflected CR wave is isolated from the received signals, which is a CR wave that has reflected off of the reflecting layer (10) below the one or more receivers (60). A seismic profile of the multi-layered subsurface formation is created, using the at least one reflected CR wave. Time-lapse seismic monitoring of hydrocarbon extraction operations, such as steam injection, is also provided.

Abstract: A method may include providing a sensor in a first wellbore segment, providing a sensor in a second wellbore segment, observing upgoing acoustic waves or downgoing acoustic waves with the sensors, and separating the upgoing acoustic waves and/or the downgoing acoustic waves from a total wavefield. The first wellbore segment and the second wellbore segment may be separated by a distance. At least one of the wellbore segments may be non-vertical and/or the first wellbore segment may not be parallel to the second wellbore segment. The first wellbore segment may be part of a first set of wellbores and the second wellbore segment may be part of a second set of wellbores. The separated upgoing and downgoing acoustic waves may be used to generate deghosted data.

Abstract: A method for obtaining information about a hydraulic fracturing operation in a fracture zone in a well, comprises a) providing at least one acoustic sensor in the well and at least one acoustic source, b) injecting fracturing fluid into the well so as to cause fractures in a fracture zone in the surrounding formation, c) using the acoustic source to send an acoustic signal and using the acoustic receiver to receive the signal, d) repeating step c) at least once, and e) processing the received signals using a microprocessor so as to obtain information about the fractures. The source may be at the earth's surface or in a second well. Step e) may comprise measuring first-arriving acoustic waves or measuring reflected or diffracted acoustic waves. The information gained in step e) may be used to control the injection of fracturing fluid or detect out-of-zone water injection.

Abstract: A method for determining the physical location of a fiber optic channel in a fiber optic cable comprises the steps of a) providing at least one location key having a known physical location, b) establishing the location of the location key with respect to the fiber optic channel, and c) using the location information established in step b) to determine the physical location of the channel. The location key may comprises an acoustic source, a section of fiber optic cable that is acoustically masked, or at least one magnetic field source and step b) comprises using a Lorentz force to establish the location of the magnetic field source with respect to the fiber optic channel.

Abstract: A method for obtaining information about a subsurface formation from acoustic signals that contain information about the subsurface formation, comprises a) transmitting an optical signal into a fiber optic cable (14) that includes a sensing apparatus (20) comprising a plurality of substantially parallel fiber lengths (24), b) collecting from the sensing apparatus a plurality of received optical signals, each received signal comprising a portion of the transmitted signal that has been reflected from a different segment of a cable length, wherein the different segments are each in different cable lengths and correspond to a single selected location along the sensing cable, and c) processing the collected signals so as to obtain information about an acoustic signal received at the different segments. The cable may be ribbon cable and the lateral distance between the different segments may be less than 10 meters.

Abstract: A Distributed Acoustic Sensing(DAS) fiber optical assembly comprises adjacent lengths of optical fiber A, B with different directional acoustic sensitivities, for example by providing the first length of optical fiber A with a first coating 35, such as acrylate, and the second length of optical fiber B with a second coating 36, such as copper, wherein the first and second coatings 35 and 36 may be selected such that the Poisson's ratio of the first length of coated fiber A is different from the Poisson's ratio of the second length of coated fiber B. The different Poisson's ratios and/or other properties of the adjacent lengths of optical fiber A and B improve their directional acoustic sensitivity and their ability to detect broadside (radial) acoustic waves.

Abstract: A method for obtaining seismic information about a subsurface formation using at least one fiber optic cable having its proximal end coupled to a light source and a photodetector comprises: transmitting into the cable at least one light pulse; receiving at the photodetector a first and second light signals indicative of the physical status of at least one first cable section and at least one second cable section, respectively, wherein the first and second sections are selected so as to provide first and second information items, respectively; optionally, further processing at least one of the first and second information items so as to produce derivative information; and outputting at least one of the first, second, and derivative information items to a display; wherein the second item differs from the first item in at least one aspect selected from the group consisting of: resolution, area, and location.

Abstract: A method for collecting information about a subsurface region, comprises a) providing a set of data comprising a plurality of scattered signals, where each scattered signal is a portion of an acoustic seismic signal that has been scattered by and at least one scatterer and received at a receiver, b) using spatial deconvolution to process the scattered signals so as generate a coherent arrival, and c) using the coherent arrival to output human readable information about the subsurface region. The receiver may be a geophone or a fiber optic distributed acoustic sensor and may be in a borehole or at the surface. The acoustic seismic signal may originate at the surface or below the surface and may be an active or passive source.

Abstract: A method of marine time-lapse seismic surveying of a subsurface formation, comprises providing a baseline survey, providing a monitor survey that includes information about changes in the subsurface relative to the baseline survey, recording a repeat survey so closely in time to one of either the baseline survey or the monitor survey that changes in the subsurface can be ignored but under different near-surface conditions from said one survey, computing a short-time survey difference between the repeat signals and signals comprising said one of either the baseline survey or the monitor survey, computing a monitor survey difference, matching the short-time survey difference and the monitor survey difference to derive a matched noise survey difference, subtracting the matched noise survey difference from the monitor survey difference, and outputting a noise suppressed survey difference based on the result of the subtraction.

Abstract: A method for obtaining information about a hydraulic fracturing operation in a fracture zone in a well, comprises a) providing at least one acoustic sensor in the well and at least one acoustic source, b) injecting fracturing fluid into the well so as to cause fractures in a fracture zone in the surrounding formation, c) using the acoustic source to send an acoustic signal and using the acoustic receiver to receive the signal, d) repeating step c) at least once, and e) processing the received signals using a microprocessor so as to obtain information about the fractures. The source may be at the earth's surface or in a second well. Step e) may comprise measuring first-arriving acoustic waves or measuring reflected or diffracted acoustic waves. The information gained in step e) may be used to control the injection of fracturing fluid or detect out-of-zone water injection.

Abstract: A method for determining the physical location of a fiber optic channel in a fiber optic cable comprises the steps of a) providing at least one location key having a known physical location, b) establishing the location of the location key with respect to the fiber optic channel, and c) using the location information established in step b) to determine the physical location of the channel. The location key may comprises an acoustic source, a section of fiber optic cable that is acoustically masked, or at least one magnetic field source and step b) comprises using a Lorentz force to establish the location of the magnetic field source with respect to the fiber optic channel.

Abstract: A Distributed Acoustic Sensing (DAS) fiber optical assembly comprises adjacent lengths of optical fiber A, B with different directional acoustic sensitivities, for example by providing the first length of optical fiber A with a first coating 35, such as acrylate, and the second length of optical fiber B with a second coating 36, such as copper, wherein the first and second coatings 35 and 36 may be selected such that the Poisson's ratio of the first length of coated fiber A is different from the Poisson's ratio of the second length of coated fiber B. The different Poisson's ratios and/or other properties of the adjacent lengths of optical fiber A and B improve their directional acoustic sensitivity and their ability to detect broadside (radial) acoustic waves.

Abstract: A method for obtaining information about a subsurface formation from acoustic signals that contain information about the subsurface formation, comprises a) transmitting an optical signal into a fiber optic cable (14) that includes a sensing apparatus (20) comprising a plurality of substantially parallel fiber lengths (24), b) collecting from the sensing apparatus a plurality of received optical signals, each received signal comprising a portion of the transmitted signal that has been reflected from a different segment of a cable length, wherein the different segments are each in different cable lengths and correspond to a single selected location along the sensing cable, and c) processing the collected signals so as to obtain information about an acoustic signal received at the different segments. The cable may be ribbon cable and the lateral distance between the different segments may be less than 10 meters.

Abstract: A method for obtaining seismic information about a subsurface formation using at least one fiber optic cable having its proximal end coupled to a light source and a photodetector comprises: transmitting into the cable at least one light pulse; receiving at the photodetector a first and second light signals indicative of the physical status of at least one first cable section and at least one second cable section, respectively, wherein the first and second sections are selected so as to provide first and second information items, respectively; optionally, further processing at least one of the first and second information items so as to produce derivative information; and outputting at least one of the first, second, and derivative information items to a display; wherein the second item differs from the first item in at least one aspect selected from the group consisting of: resolution, area, and location.

Abstract: A method for monitoring a multi-layered system below a surface comprising a slow layer and a fast layer; the method comprising: transmitting one or more seismic waves from one or more seismic sources through the multi-layered system; receiving signals emanating from the multi-layered system in response to the one or more seismic waves with one or more receivers located a distance from the one or more seismic sources; identifying one or more critically refracted compressional (CRC) waves amongst the signals; and inferring information about a change in the slow layer based on the one or more CRC waves; wherein the CRC wave is a refracted wave which has traveled along an interface between the fast layer and an adjacent layer.

Abstract: A method of monitoring a subsurface formation (2) including a region of interest (1), below a surface region, which method comprises the steps of exciting seismic interface waves (14), in the surface region over an area of the earth's surface at a first and a second moment in time; detecting seismic interface waves signals for a plurality of locations in the area; determining, from the detected seismic interface wave signals, an areal distribution of a parameter related to seismic interface wave velocity change between the first and second moments in time; and inferring, from the areal distribution, an indication of a volume change of the region of interest between the first and second moments in time.

Abstract: A method of marine time-lapse seismic surveying of a subsurface formation, comprises providing a baseline survey, providing a monitor survey that includes information about changes in the subsurface relative to the baseline survey, recording a repeat survey so closely in time to one of either the baseline survey or the monitor survey that changes in the subsurface can be ignored but under different near-surface conditions from said one survey, computing a short-time survey difference between the repeat signals and signals comprising said one of either the baseline survey or the monitor survey, computing a monitor survey difference, matching the short-time survey difference and the monitor survey difference to derive a matched noise survey difference, subtracting the matched noise survey difference from the monitor survey difference, and outputting a noise suppressed survey difference based on the result of the subtraction.

Abstract: A method for monitoring the movement of fluid through a subsurface formation of interest, comprising: a) providing a set of signals obtained by transmitting seismic waves through the formation of interest and receiving signals emanating from the multi-layered system in response to the seismic waves with one or more receivers located a distance from the seismic source(s), b) identifying one or more critically refracted waves among the signals so as to generate a first data set of refracted signals, c) repeating steps a) and b) after a period of time so as to generate a second data set of refracted signals, d) comparing the second data set to the first data set so as to generate a time-lapse data set, e) imaging the time-lapse data set using travel time tomography; and f) inferring information about the movement of fluid based on the image generated in step e).

Abstract: A method for monitoring a multi-layered system below a surface comprising a slow layer and a fast layer; the method comprising: transmitting one or more seismic waves from one or more seismic sources through the multi-layered system; receiving signals emanating from the multi-layered system in response to the one or more seismic waves with one or more receivers located a distance from the one or more seismic sources; identifying one or more critically refracted compressional (CRC) waves amongst the signals; and inferring information about a change in the slow layer based on the one or more CRC waves; wherein the CRC wave is a refracted wave which has traveled along an interface between the fast layer and an adjacent layer.