Western Atlas International, Inc.

Baker Hughes Corporation

Xiaoming Tang

Raghu K Chunduru

Arthur C Cheng

Michael A Frenkel

Alberto G Mezzatesta

Kurt-M Strack

Kurt-Martin Strack

Stephan Gelinsky

Tianrun Zhang

Ningya Cheng

Keeva Vozoff

Gang Yu

Acoustic logging data are obtained using a logging tool including at least on transmitter and a plurality of receivers. A waveform matching inversion is performed to obtain formation slowness profiles at various resolutions ranging from the total length of the receiver array to the inter-array receiver spacing. Using overlapping sub-arrays of reduced aperture provides for resolution enhancement. The enhancement is achieved by minimizing the noise contamination effects by maximizing the information redundancy in waveform data. The method achieves this by isolating the wave event of interest and matching the waveform of the event for all possible receiver pairs allowed by the sub-array. The high-resolution slowness curve successfully resolves the laminated features in a geological formation. This invention is a useful tool for evaluating thin beds in laminated formations using borehole acoustic logging.

Method for enhancing resolution of earth formation elastic-wave velocities by isolating a wave event and matching it for all receiver combinations on an acoustic-array logging tool

A system and method to determine an in-situ stress field based on borehole acoustic monopole and cross-dipole measurements. A radially polarized monopole shear-wave is generated in a borehole. It is then determined whether the shear-wave has split into two shear-waves. If it has, the difference in velocities between the two split shear-waves is used to determine the stress induced anisotropy around and near the borehole. The difference in velocities of cross-dipole shear-waves and the direction of the fast shear-wave are measured and used to determine the magnitude of the maximum shear stress and the maximum stress orientation of the geologic formation. Furthermore, a method of determining the stress-velocity coupling coefficients from laboratory measurements as well as through field measurement calibration is disclosed. The effect of borehole pressure on the field measurement calibration method of determining the stress-velocity coupling coefficients is taken into account. Additionally disclosed is a method for defining a stress indicator that is related to stress-caused rock deformation. This stress indicator can be used to determine if rock failure is impending and is useful in sand control and borehole stability applications.

Estimating formation stress using borehole monopole and cross-dipole

A method of joint inversion processing acoustic velocity and electrical resistivity well log data. The method includes generating an initial model of earth formations over an interval of interest. The initial model corresponds to earth formations for which the acoustic velocity and resistivity well log data have been measured. The initial model includes layers each having a geometry, a value of resistivity and a value of acoustic velocity. Acoustic velocity and resistivity data are synthesized based on the initial model. Differences are determined between the synthesized data and the measured data. The initial model is adjusted and the steps of synthesizing the log data and determining the differences are repeated until the differences reach a minimum, thereby generating a final model of the earth formations. The step of adjusting includes determining a coupling relationship between the acoustic velocity and the resistivity for the earth formations, and generating an inverse Jacobian matrix of sensitivity functions of the resistivity and acoustic velocity with respect to the geometry and the coupling relationship.

Joint inversion processing method for resistivity and acoustic well log

A method for estimating porosity of an earth formation from measurements of acoustic energy traversing the earth formation and from measurements of seismoelectric voltages generated in the formation in response to the acoustic energy. The method includes the steps of measuring the acoustic energy traversing the earth formation and measuring said seismoelectric voltages generated in response to the acoustic energy traversing the formation. A seismoelectric signal is synthesized from the measurements of the acoustic energy using an initial value of the porosity. A difference is determined between the synthesized seismoelectric voltages and the measured seismoelectric voltages. The initial value of porosity is adjusted, and the steps of synthesizing the seismoelectric voltages from the acoustic signal, determining the difference, and adjusting the value of porosity are repeated until the difference drops below a predetermined threshold or the difference reaches a minimum value. The adjusted value of porosity which results in the difference being at the minimum is taken as the formation porosity. A particular embodiment includes estimating conductivity of fluid in the pore spaces of the formation by calculating the synthetic seismoelectric voltages using an initial value of conductivity; determining a difference between the synthetic seismoelectric voltages and the measured seismoelectric voltages; and adjusting the initial value of conductivity, and repeating the steps of calculating the synthetic seismoelectric voltages, determining the difference and adjusting the value of conductivity until the difference reaches a minimum.

Apparatus and method for combined acoustic and seismoelectric logging

A method for determining the permeability of earth formations penetrated by a wellbore from acoustic signals measured by an acoustic wellbore logging instrument. The method includes separating components from the measured acoustic signals which represent Stoneley waves propagating through the earth formations. Signals representing Stoneley waves propagating through the same earth formations are synthesized. The separated acoustic signal components and the synthesized Stoneley wave signals are compared. The permeability is determined from differences between the synthesized Stoneley wave signals and the separated acoustic signal components. In a preferred embodiment, the step of calculating the permeability includes inversion processing a wave center frequency shift and a wave travel time delay with respect to the permeability of the earth formations.

Method for estimating permeability of earth formations by processing

A method of determining the acoustic propagation velocities of earth formations using signals generated by an acoustic array well logging instrument. The method includes generating a model of the acoustic velocities including a value of velocity for each propagation mode for which the velocity is to be determined Acoustic waveforms are synthesized for a plurality of receiver locations on the acoustic logging instrument by using the values of the acoustic velocities in the model. A difference is determined between the synthesized waveforms and measured waveforms generated by acoustic energy detected at corresponding receiver locations on the acoustic logging instrument. The model is adjusted and the waveforms are resynthesized until the difference is determined to be at a minimum. The step of adjusting the model is performed by very fast simulated annealing.

Method for determining acoustic velocity of earth formations by

A method for determining orientations and velocities of slow and fast waves in an anisotropic earth formation. Signals are used from an acoustic logging tool including dipole transmitters and receiver arrays. An initial value of angle subtended between orientation of the fast wave and one of the transmitters is selected. A waveform of a fast principal wave and slow principal wave at first and second selected receiver positions are calculated from received signals at each of these positions and the selected subtended angle. A derivative waveform with respect to subtended angle is calculated for both fast and slow principal waves. An initial velocity of slow waves is selected and the calculated waveforms of the slow principal wave and its derivative waveform at the first position are time shifted by a time corresponding to distance between first and second receiver positions and the selected value of velocity. A value of difference in velocity between slow waves and fast waves is selected, and the time-shifted slow principal wave and its derivative waveform are adjusted by a time corresponding to the value of difference in velocities. Differences between the time-adjusted wave and its derivative waveform are determined between the calculated fast principal wave and its derivative waveform calculated at that receiver position. The value of velocity, value of difference in velocity and subtended angle are adjusted and calculating waveforms and derivative waveforms, time shifting and time adjusting are repeated until the difference between waveforms reaches a minimum.

Method for determining earth formation shear wave anisotropy parameters

A method for detecting alteration of earth formations penetrated by a wellbore. The method includes determining a first arrival velocity of dipole acoustic energy propagated through the earth formations. A first frequency dependent velocity of the dipole acoustic energy is then determined. A first dispersion characteristic is determined from the difference between the first arrival and frequency dependent velocities. The method includes determining a frequency dependent velocity and a first arrival velocity for synthesized waveforms for an unaltered formation. The synthesis uses the first arrival velocity of the dipole acoustic energy as a shear velocity. A second dispersion characteristic, related to a difference between the frequency dependent velocity and the first arrival velocity of the synthesized waveforms is determined. The alteration is detected by finding a difference between the first dispersion characteristic and the second dispersion characteristic. In a preferred embodiment, the frequency dependent velocity includes a peak energy velocity determined by waveform matching the receiver signals.

Method for identifying alteration of earth formations using dipole

A method for modeling fracture zones in the sidewall of a borehole and for estimating the hydraulic conductivity thereof. The method first separates Stoneley wavefields into a directly-transmitted wavefield and a one-way (i.e. downgoing) reflected wavefield from which the depth configuration may be determined. The separated wavefields are corrected for the effects of borehole irregularity due to such effects as washouts and the like by numerically modeling Stoneley wave propagation using caliper and slowness measurements. The hydraulic conductivity is estimated from parameters derived from synthetic and measured Stoneley-wave data across the fracture zone in combination with measurements of the borehole radius.

Method for estimating the hydraulic conductivity of a borehole sidewall

A method of determining the acoustic propagation velocity of an earth formation penetrated by a wellbore by processing signals from an array acoustic wellbore logging tool. The tool includes a transmitter and a plurality of receivers axially spaced apart from the transmitter. The method includes the steps of combining signals generated by ones of the receivers in response to acoustic energy propagated through the wellbore from the transmitter, to generate a synthesized signal corresponding to another one of the receivers. The step of combining includes time shifting signals from the ones of the receivers by an amount corresponding to a predetermined velocity for each propagation mode and the axial distance between the ones of receivers and the other receiver. The synthesized signal is compared to the signal generated at the other receiver in response to the acoustic energy to determine a degree of correspondence between the synthesized signal and the received signal. The values of velocity for each propagation mode are varied, a signal is again synthesized and compared to the measured signal, and these steps are repeated until the degree of correspondence reaches a maximum. The values of velocity at which the degree of correspondence is a maximum are determined to be the acoustic propagation velocities of the earth formation for each of the different modes of propagation. In a preferred embodiment of the invention, the step of comparing includes generating an object function of the difference between the synthesized signal and the received signal. The object function is minimized by the Levenberger-Marquardt algorithm to determine the values of velocity for each propagation mode.

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Sugar Land, TX, United States of America

Xiaoming Tang