Abstract: A method for monitoring fluid flow through a downhole device, comprises a) providing an acoustic tube wave in fluid in the device; b) measuring the acoustic tube wave after it has passed through the fluid in the device; and c) assessing the permeability of the device by measuring the attenuation of the acoustic signal. Changes in velocity of the acoustic signal may also be measured. The device may be a permeable downhole device such as a sand screen the measurements in step b) are made using a plurality of sensors deployed in the hole. The method may further including the step of cross-correlating a signal received at a first receiver with signals received at additional sensors so as to obtain an effective response as if the signal had been emitted from a source at the position of said first receiver.

Abstract: A method for imaging a subsurface formation using at least two seismic sources and receivers includes: a) creating a wave field in the formation, b) obtaining a set of responses for each receiver and performing wave field separation on them, c) obtaining a virtual source signal for at least a first receiver k by cross-correlating at least part of the response of a second receiver m with at least part of the response of the first receiver k and summing the cross-correlated responses from the sources, making receiver k a virtual source, d) for each virtual source, estimating an amplitude radiation pattern by performing a transform of the response data, e) deconvolving at least one virtual source signal with at least part of the estimated radiation pattern for that receiver to produce an amplitude-corrected virtual source signal, and f) using that signal to create an image of the subsurface formation.

Abstract: Method of imaging seismic data recorded using a set of seismic receivers positioned to receive seismic responses from a subsurface formation upon activating a seismic source. The seismic responses are direction-sensitive responses. A virtual signal received by receiver k from the virtual source at the position of receiver m is determined by processing involving cross correlating at least part of the responses of a receiver m with at least part of the responses of a seismic receiver k. Part of direction-sensitive responses or part of the virtual signal that contains a component of the wave field at receiver m traveling in a first direction and part of the direction-sensitive responses or part of the virtual signal that contains a component of the wave field at the receiver k traveling in a second direction may be removed.

Abstract: A method for imaging a subsurface formation using at least two seismic sources and receivers comprises: a) creating a wave field in the formation, b) obtaining a set of responses for each receiver and performing wave field separation on them, c) obtaining a virtual source signal for at least a first receiver k by cross-correlating at least part of the response of a second receiver m with at least part of the response of the first receiver k and summing the cross-correlated responses from the sources, making receiver k a virtual source, d) for each virtual source, estimating an amplitude radiation pattern by performing a transform of the response data, e) deconvolving at least one virtual source signal with at least part of the estimated radiation pattern for that receiver to produce an amplitude-corrected virtual source signal, and f) using that signal to create an image of the subsurface formation.

Abstract: A method for monitoring fluid flow through a downhole device, comprises a) providing an acoustic tube wave in fluid in the device; b) measuring the acoustic tube wave after it has passed through the fluid in the device; and c) assessing the permeability of the device by measuring the attenuation of the acoustic signal. Changes in velocity of the acoustic signal may also be measured. The device may be a permeable downhole device such as a sand screen the measurements in step b) are made using a plurality of sensors deployed in the hole. The method may further including the step of cross-correlating a signal received at a first receiver with signals received at additional sensors so as to obtain an effective response as if the signal had been emitted from a source at the position of said first receiver.

Abstract: Method of imaging seismic data recorded using a set of seismic receivers positioned to receive seismic responses from a subsurface formation upon activating a seismic source. The seismic responses are direction-sensitive responses. A virtual signal received by receiver k from the virtual source at the position of receiver m is determined by processing involving cross correlating at least part of the responses of a receiver m with at least part of the responses of a seismic receiver k. Part of direction-sensitive responses or part of the virtual signal that contains a component of the wave field at receiver m traveling in a first direction and part of the direction-sensitive responses or part of the virtual signal that contains a component of the wave field at the receiver k traveling in a second direction may be removed.

Abstract: A seismic velocity profile in a region of interest in a subsurface formation is determined using at least the following steps. (a) Activating a seismic source at a location n, thereby exciting a wave in the subsurface formation. (b) Recording a wave signal trace unm(t) against time t, at a seismic receiver m. (c) Recording a wave signal trace unk(t) against time t at a seismic receiver k. (d) Cross correlating the wave signal traces unm(t) and unk(t) to obtain uconvnmnk(t). (e) Repeating these steps, for different locations n; (f) Summing uconvnmnk(t) over all locations n, to obtain a signal trace uvsmk(t) which corresponds to the signal received by the seismic receiver k from the virtual source at the position of seismic receiver m; (g) Deriving the seismic velocity based on the time of first arrival of the wave in uvsmk(t) and the predetermined distance between the seismic receiver m and the seismic receiver k.