Abstract: A method for determining hypocenters of microseismic events includes entering as input to a computer seismic signals recorded by a plurality of seismic sensors disposed proximate a volume of subsurface to be evaluated. For each point in space in the volume, and for a plurality of preselected origin times, a seismic energy arrival time at each seismic sensor is determined. Event amplitudes for each arrival time are determined. A synthetic event amplitude is calculated for each arrival time. A semblance between the determined event amplitudes and the synthetic event amplitudes is determined. Existence of an actual microseismic is determined event when the semblance exceeds a selected threshold.

Abstract: A method for determining hypocenters of microseismic events includes entering as input to a computer seismic signals recorded by a plurality of seismic sensors disposed proximate a volume of subsurface to be evaluated. For each point in space in the volume, and for a plurality of preselected origin times, a seismic energy arrival time at each seismic sensor is determined. Event amplitudes for each arrival time are determined. A synthetic event amplitude is calculated for each arrival time. A semblance between the determined event amplitudes and the synthetic event amplitudes is determined. Existence of an actual microseismic is determined event when the semblance exceeds a selected threshold.

Abstract: A method for determining positions and origin times of seismic events occurring in the Earth's subsurface includes accepting as input to the method signals recorded from a plurality of seismic sensors deployed above a subsurface volume of interest. The recorded signals are a representation of seismic amplitude with respect to time. Origin time and location of each of a plurality of subsurface seismic events are determined from the recorded signals. The origin times and locations of each event are inverted to obtain Thomsen's parameters in formations in the volume of interest. Depths of each of the events are determined by individually searching the depth of each event, the inversion with each incorporated new depth including updating the Thomsen parameters and setting as a limit a minimum value of RMS error.

Abstract: A microseismic method of determining the position of a downhole receiver (4) making use of received signals from events (21, 22) at least two known locations using the equivalent of a Thales circle construction from two or more pairs of events.

Abstract: A method for estimating moment magnitude of a seismic event occurring in subsurface formations includes measuring seismic signals at each of a plurality of seismic sensors disposed in a selected pattern proximate a subsurface area in which the seismic event occurs. Amplitude events corresponding to the seismic event from the signals detected by each receiver are time aligned. Corrections are applied to the aligned events for density, for the formation velocity, for the radiation pattern, for propagation effects and instrument response. The corrected events are summed. Seismic moment is determined from the summed, corrected events. A moment magnitude is estimated from the seismic moment.

Abstract: The invention pertains generally to the field of seismicity. The method of the invention provides an objective criteria for decision when determining whether or not the seismic activity (seismicity) occurring within a certain area is induced by human activity, specifically geophysical activity, particularly associated with the mining/extracting industry, or whether the seismicity is naturally occurring. The method can be useful for production companies, regulatory authorities, or insurance companies.

Abstract: A method for mapping a fracture network that includes determining a source of at least one seismic event from features in recorded seismic signals exceeding a selected amplitude (“visible seismic event”). The signals are generated by a plurality of seismic receivers disposed proximate a volume of subsurface to be evaluated. The signals are electrical or optical and represent seismic amplitude. A source mechanism of the at least one visible seismic event is determined. A fracture size and orientation are determined from the source mechanism. Seismic events are determined from the signals from features less than the selected amplitude (“invisible seismic events”) using a stacking procedure. A source mechanism for the invisible seismic events is determined by matched filtering. At least one fracture is defined from the invisible seismic events. A fracture network model is generated by combining the fracture determined from the visible seismic event with the fracture determined from the invisible seismic events.

Abstract: A method for passive seismic surveying includes deploying seismic sensors in a plurality of spatially distributed wellbores disposed above a volume of subsurface formations to be evaluated. The sensors in each wellbore form a line of sensors. Each sensor generate optical or electrical signals in response to seismic amplitude. The seismic signals from each sensor are recorded for a selected period of time. The response of the seismic sensor recordings is beam steered to at least one of a selected point and a selected volume in the subsurface. At least one microseismic event is identified in the beam steered response.

Abstract: A method for determining positions and origin times of seismic events occurring in the Earth's subsurface includes accepting as input to the method signals recorded from a plurality of seismic sensors deployed above a subsurface volume of interest. The recorded signals are a representation of seismic amplitude with respect to time. Origin time and location of each of a plurality of subsurface seismic events are determined from the recorded signals. The origin times and locations of each event are inverted to obtain Thomsen's parameters in formations in the volume of interest. Depths of each of the events are determined by individually searching the depth of each event, the inversion with each incorporated new depth including updating the Thomsen parameters and setting as a limit a minimum value of RMS error.

Abstract: A method for locating origin time, origin location and source mechanism of seismic events occurring in a selected volume of subsurface formations includes calculating a travel time from each possible origin location to each of a plurality of seismic receivers disposed above the volume in a selected pattern. A signal amplitude is measured by each receiver for each possible origin time at each possible origin location. The signal amplitude is determined from the continuously recorded data by calculating travel time delays for each possible origin location and origin time. The deviatoric moment tensors are determined from the signal amplitudes by moment tensor inversion restricted to deviatoric moment tensors. A norm for each deviatoric moment tensor is generated. An origin time, origin position and source mechanism of a seismic event is determined wherein any norm exceeds a selected threshold.

Abstract: A method for passive seismic surveying includes deploying seismic sensors in a plurality of spatially distributed wellbores disposed above a volume of subsurface formations to be evaluated. The sensors in each wellbore form a line of sensors. Each sensor generate optical or electrical signals in response to seismic amplitude. The seismic signals from each sensor are recorded for a selected period of time. The response of the seismic sensor recordings is beam steered to at least one of a selected point and a selected volume in the subsurface. At least one microseismic event is identified in the beam steered response.

Abstract: A method for seismic event mapping includes selecting a plurality of subvolumes representing possible locations of origin of a seismic event in the Earth's subsurface. For each subvolume a plurality of possible directions of motion of subsurface formations is selected. For each subvolume and each possible direction of motion, polarity correction is applied to seismic signals recorded at a plurality of positions proximate a volume of the Earth's subsurface to be evaluated. The polarity correction is based on the direction of motion and the position of each seismic sensor with respect to the subvolume. The recorded, polarity corrected seismic signal recordings are time aligned. The time aligned recordings are summed. A most likely direction of motion and subvolume position are determined based on a selected attribute of the summed, time aligned seismic signals.

Abstract: A method for mapping a fracture network that includes determining a source of at least one seismic event from features in recorded seismic signals exceeding a selected amplitude (“visible seismic event”). The signals are generated by a plurality of seismic receivers disposed proximate a volume of subsurface to be evaluated. The signals are electrical or optical and represent seismic amplitude. A source mechanism of the at least one visible seismic event is determined. A fracture size and orientation are determined from the source mechanism. Seismic events are determined from the signals from features less than the selected amplitude (“invisible seismic events”) using a stacking procedure. A source mechanism for the invisible seismic events is determined by matched filtering. At least one fracture is defined from the invisible seismic events. A fracture network model is generated by combining the fracture determined from the visible seismic event with the fracture determined from the invisible seismic events.

Abstract: A microseismic method of determining the position of a downhole receiver (4) making use of received signals from events (21, 22) at least two known locations using the equivalent of a Thales circle construction from two or more pairs of events.

Abstract: A method for seismic event mapping includes selecting a plurality of subvolumes representing possible locations of origin of a seismic event in the Earth's subsurface. For each subvolume a plurality of possible directions of motion of subsurface formations is selected. For each subvolume and each possible direction of motion, polarity correction is applied to seismic signals recorded at a plurality of positions proximate a volume of the Earth's subsurface to be evaluated. The polarity correction is based on the direction of motion and the position of each seismic sensor with respect to the subvolume. The recorded, polarity corrected seismic signal recordings are time aligned. The time aligned recordings are summed. A most likely direction of motion and subvolume position are determined based on a selected attribute of the summed, time aligned seismic signals.

Abstract: A microseismic method of monitoring fracturing operation or other passive seismic events in hydrocarbon wells is described using the steps of obtaining multi-component s-wave signals of the event; and using a linear derivative of S-wave arrival times of the signals in a first direction, an S-wave velocity and an s-wave polarization to determine at least two components of the S-wave slowness vector.

Abstract: A method for determining seismic anisotropy of subsurface rock formations includes measuring passive seismic signals at a plurality of locations above an area of the Earth's subsurface to be surveyed. The compressional- and shear-wave arrival times from at least one origin location of a seismic event occurring in the subsurface are determined from the measured seismic signals. The arrival times are inverted to obtain values of the seismic anisotropy parameters.

Abstract: A method of identifying passive seismic events in seismic data that contains at least first seismic data traces acquired at a first seismic receiver and second seismic data traces acquired at a second receiver spatially separated from the first receiver comprises determining an overall measure of similarity for a pair of events in the seismic traces. The overall measure of similarity is indicative of similarity between the events acquired at the first seismic receiver and of similarity between the events acquired at the second seismic receiver. In one method, the overall measure of similarity is an overall cross-correlation coefficient. The overall cross-correlation coefficient is found by determining a first correlation coefficient for the pair of events from the data acquired at the first receiver and determining a second correlation coefficient for the pair of events from the data acquired at the second receiver.

Abstract: A microseismic method of monitoring fracturing operation or other microseismic events in hydrocarbon wells is described using the steps of obtaining multi-component signal recordings from a single monitoring well in the vicinity of a facture or event; and rotating observed signals such that they become independent of at least one component of the moment tensor representing the source mechanism and performing an inversion of the rotated signals to determine the remaining components.

Abstract: A method for determining presence of seismic events in seismic signals includes determining presence of at least one seismic event in seismic signals corresponding to each of a plurality of seismic sensors. A correlation window is selected for each of the plurality of seismic signals. Each correlation window has a selected time interval including an arrival time of the at least one seismic event in each seismic signal. Each window is correlated to the respective seismic signal between a first selected time and a second selected time. Presence of at least one other seismic event in the seismic signals from a result of the correlating.