Western Atlas International, Inc.

Baker Hughes Corporation

Arthur C Cheng

Xiaoming Tang

Raghu K Chunduru

Kurt-Martin Strack

Ningya Cheng

Gang Yu

Stephan Gelinsky

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 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

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Houston, TX, United States of America

Arthur C Cheng