A computer-implemented method can include the following. Seismic vibratory waves through the Earth along a selected vector path are received. An initial value is selected for a first arrival for each of the seismic vibratory waves. Initial values are determined for travel times and velocities of the seismic vibratory waves. Reversed signs of amplitudes of the seismic vibratory waves are determined and corrected. Time intervals are determined based on the initial values of the travel times. Time windowing and filtering in a frequency domain are performed. Final values are determined for first arrivals and travel times for each of the seismic vibratory waves based on the time windowing and filtering. Final values are determined for velocities of the seismic vibratory waves.

Systems and methods for estimating orthorhombic anisotropy parameters of subsurface rock layers are provided. An initial three-dimensional (3D) model of layers in a subsurface formation is generated. Particular combinations of seismic source and receiver locations associated with a vertical seismic profile (VSP) survey of the formation are selected based on a simulation of seismic wave propagation through each layer of the initial 3D model. A global inversion is performed using data points selected from travel time data associated with the VSP survey in order to estimate different sets of anisotropy parameters for the layers of the initial 3D model, where the selected data points correspond to the selected source-receiver combinations. The initial 3D model is refined with an optimal set of anisotropy parameters selected from the estimated parameter sets. The refined 3D model is provided for seismic analysis and well planning operations to be performed for the subsurface formation.

A method for borehole measurements may comprise receiving one or more signals from a linear receiver array, computing an arctan of a Hilbert Transform, isolating a first arriving energy, selecting a reference instantaneous phase on a reference receiver, finding the reference instantaneous phase for the linear receiver array, computing a relative travel time shift, combining a reference pick time with a relative time, and determining a travel time. A system for borehole measurements comprise a conveyance, a bottom hole assembly attached to the conveyance, a linear receiver array, wherein the linear receiver array is disposed on the bottom hole assembly, and a computer system connected to the linear receiver array.

A retrofit valve shutoff device comprises a coupling key for coupling with an actuator of a shutoff valve, an accelerometer for making acceleration measurements in three directions, a motor, and a processing unit. The processing unit determines the arrival of seismic P-waves when the ratio of vibrations' power in the vertical direction with respect to a sum of the vibrations' power in the three directions exceeds a first threshold. The processing unit then determines the arrival of seismic S-waves when the sum of the vibrations' power in the three directions exceeds a second threshold. The processing unit then determines the arrival of seismic surface waves when the sum of the vibrations' power in the three directions exceeds a third threshold. The processing unit then sends a signal to the motor to rotate the coupling key and the actuator of the shutoff valve to close the shutoff valve.

Limitations in accuracy and computing power requirements impeding conventional Kirchhoff migration and reverse time migration are overcome by using the wave-equation Kirchhoff, WEK, technique with Kirchhoff migration. WEK technique includes forward-propagating a low-frequency wavefield from a shot location among pre-defined source locations, calculating an arrival traveltime of a maximum amplitude of the low-frequency wavefield, and applying Kirchhoff migration using the arrival traveltime and the maximum amplitude.

A method can include receiving seismic survey data of a subsurface environment from a seismic survey utilizing water bed receivers, where each of the receivers includes a clock; assessing one or more clock calibration criteria; based on the assessing, selecting a clock drift processor for processing at least a portion of the seismic survey data from a plurality of different clock drift processors; using at least the clock drift processor, performing a simultaneous inversion for values of model-based parameters; and, using at least a portion of the values, generating processed seismic survey data that represents one or more geological interfaces in the subsurface environment.

Disclosed herein is a method for eccentricity correction. This method may dispose a downhole tool into a borehole. The downhole tool may comprise a measuring assembly that has at least one transducer, determining a beam pattern from the at least one transducer, determining a center of the measurement assembly in the borehole with the beam pattern, calculating a beam pattern factor with at least the beam pattern, calculating an angle factor with at least the beam pattern, calculating an eccentricity factor with at least the beam pattern factor and the angle factor, and creating an eccentricity corrected image with at least the eccentricity factor.

A method of processing seismic data by a reflection seismic survey includes: calculating a first pseudo-water-surface reflection wave by virtually propagating a direct wave represented in the seismic data in a progressing direction of a time axis by a time in which the acoustic wave propagates in the water at a distance twice a depth of the seismic source, and further correcting an amplitude of the direct wave so that the amplitude is approximated to an amplitude of a water-surface reflection wave of the acoustic wave represented is the seismic data; and subtracting a component corresponding to the first pseudo-water-surface reflection wave from the seismic data.

Velocity tomography using time lags of wave equation migration is disclosed. Seismic tomography is a technique for imaging the subsurface of the Earth with seismic waves by generated a migration velocity model from a multitude of observations using combinations of source and receiver locations. The migration velocity model may be updated in order to reduce depth differences of reflection events (also called residual depth errors (RDE)). Direct measurement of RDE may be difficult in certain complex subsurface areas. In such areas, the RDE may be reconstructed based on time lags of wave equation migration and then used to update the migration velocity model. In particular, the RDE may be directly reconstructed from the time lags of wave equation migration, such as based on a direct relation between RDE and the time lags.

The thickness of subsurface layers if they had remained as they were prior to compaction may be estimated by restoring the volume of void space lost during compaction. Decompacted depths below seafloor, the depths the layers would be if compaction had not occurred, may be determined for the layers. A surrogate decompaction velocity may then be determined by dividing the decompacted depths by the travel times of acoustic waves that reflect off layers within the subsurface region. The decompaction velocity may be used in post-processing of acoustic data to produce a decompacted digital representation of the subsurface region. The decompacted digital representation may be used to directly interpret the thickness of layers prior to compaction, sedimentation rates over time, fault offsets, and other phenomena distorted by compaction.