Methods of electromagnetic migration imaging of geologic formation
First Claim
1. A method of imaging-while-drilling and look-ahead imaging of a geological formation using borehole devices measuring multi-component vector and/or tensor induction logging data, said method comprising the steps of:
- a. operating one or more transmitters of a device representing an electromagnetic logging instrument formed by one or more induction and/or galvanic transmitters and one or more electric and/or magnetic field receivers to generate an electromagnetic field comprising a harmonic (frequency domain) and/or pulse (time domain) field, whereby said generated electromagnetic field propagates through geological formations penetrated by the borehole and ahead of the device in a wellbore;
b. measuring at least one component of electric and/or magnetic field data with said one or more receivers;
c. conceptually replacing the one or more receivers with an array of electric and/or magnetic dipole transmitters respectively, the electric and/or magnetic moment of each conceptual dipole transmitter replicating the actually measured electric and/or magnetic field in the corresponding one or more receivers;
d. obtaining a migration electromagnetic field {Em, Hm} equivalent to that produced by the conceptual transmitters replacing the actual receivers and obtaining a reference field {Er, Hr} representative of a background medium consisting of said examined geological formation without the presence of an anomalous target;
e. obtaining an integrated sensitivity of the electromagnetic logging device by estimating a least square norm of the values of perturbation of at least one component of measured electromagnetic electromagnetic logging instrument tensor data at said plurality of locations due to conductivity perturbation at a specific local area of the examined geologic formation;
f. producing a migration image of said anomalous target by calculating a cross power spectra of said reference and said migration fields or cross correlation functions between said reference and said migration fields in the area around the borehole and/or ahead of the device and spatially weighting said cross power spectra or cross correlation functions with said integrated sensitivity;
g. determining the location, shape and electrical conductivity and/or resistivity of said anomalous target within the geologic formation around a borehole and/or ahead of the device in a wellbore from the said migration image.
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Abstract
Methods and systems for imaging-while-drilling and look-ahead imaging of a geological formation using a borehole devices measuring multi-component vector and/or tensor logging data. An electromagnetic field transmitter generates an electromagnetic field. Electromagnetic receivers measure the response from the geological formation around the borehole and ahead of the device at various receiving positions. A central processing unit may compute a migration field by simulating the replacement of the receivers with conceptual transmitters, calculate an integrated sensitivity of the recorded electromagnetic field data, compute a reference field, and calculate a cross power spectra of the reference and the migration fields or cross correlation functions between the reference and the migration fields. A spatial weighting of the cross power spectra or cross correlation functions produces a numerical reconstruction of directional images and look-ahead images of the conductivity distribution around the borehole and/or ahead of the device located within the borehole.
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Citations
20 Claims
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1. A method of imaging-while-drilling and look-ahead imaging of a geological formation using borehole devices measuring multi-component vector and/or tensor induction logging data, said method comprising the steps of:
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a. operating one or more transmitters of a device representing an electromagnetic logging instrument formed by one or more induction and/or galvanic transmitters and one or more electric and/or magnetic field receivers to generate an electromagnetic field comprising a harmonic (frequency domain) and/or pulse (time domain) field, whereby said generated electromagnetic field propagates through geological formations penetrated by the borehole and ahead of the device in a wellbore; b. measuring at least one component of electric and/or magnetic field data with said one or more receivers; c. conceptually replacing the one or more receivers with an array of electric and/or magnetic dipole transmitters respectively, the electric and/or magnetic moment of each conceptual dipole transmitter replicating the actually measured electric and/or magnetic field in the corresponding one or more receivers; d. obtaining a migration electromagnetic field {Em, Hm} equivalent to that produced by the conceptual transmitters replacing the actual receivers and obtaining a reference field {Er, Hr} representative of a background medium consisting of said examined geological formation without the presence of an anomalous target; e. obtaining an integrated sensitivity of the electromagnetic logging device by estimating a least square norm of the values of perturbation of at least one component of measured electromagnetic electromagnetic logging instrument tensor data at said plurality of locations due to conductivity perturbation at a specific local area of the examined geologic formation; f. producing a migration image of said anomalous target by calculating a cross power spectra of said reference and said migration fields or cross correlation functions between said reference and said migration fields in the area around the borehole and/or ahead of the device and spatially weighting said cross power spectra or cross correlation functions with said integrated sensitivity; g. determining the location, shape and electrical conductivity and/or resistivity of said anomalous target within the geologic formation around a borehole and/or ahead of the device in a wellbore from the said migration image. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A physical non-transitory computer readable medium having stored thereon computer executable instructions that when executed by a processor cause a computing system to perform a method of imaging-while-drilling and look-ahead imaging of a geological formation using borehole devices measuring multi-component vector and tensor induction logging data, the method comprising:
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conceptually replacing one or more electric and/or magnetic receivers of a electromagnetic logging device with one or more conceptual electric and/or magnetic dipole transmitters, wherein an electric and/or magnetic moment of each of the one or more conceptual dipole transmitters replicates an actually measured electric and/or magnetic component of a measured electromagnetic field measured by the corresponding one or more electric and/or magnetic receivers and received by the computing system, wherein the measured electromagnetic field is generated by one or more transmitters of the electromagnetic logging device placed in the borehole; calculating a migration electromagnetic field generated by the conceptual transmitters; calculating a reference electromagnetic field for the geological formation; calculating an integrated sensitivity of the electromagnetic logging device to conductivity perturbations at various locations in the geological formation; generating a migration image of a target within the geological formation based on the calculated migration electromagnetic field, reference electromagnetic field, and integrated sensitivity; and determining the location, shape and electrical conductivity of the target based on the migration image. - View Dependent Claims (11, 12)
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13. A system for imaging-while-drilling and look-ahead imaging of a geological formation using borehole devices measuring multi-component vector and tensor induction logging data comprising:
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a device representing an electromagnetic logging instrument formed by one or more induction and/or galvanic transmitters and one or more electric and/or magnetic field receivers;
the one or more transmitters configured to generate a electromagnetic field and the one or more receivers configured to measure the generated electromagnetic field; anda computing system, the computing system comprising; a processor; and one or more physical non-transitory computer readable medium having computer executable instructions stored thereon that when executed by the processor, cause the computing system to perform the following; conceptually replace one or more of the receivers with one or more conceptual electric and/or magnetic dipole transmitters, wherein an electric and/or magnetic moment of each of the one or more conceptual dipole transmitters replicates an actually measured electric and/or magnetic component of a measured electromagnetic field measured by the corresponding one or more receivers and received by the computing system, wherein the measured electromagnetic field is generated by the one or more transmitters; calculate a migration electromagnetic field generated by the conceptual transmitters; calculate a reference electromagnetic field for the geological formation; calculate an integrated sensitivity of the electromagnetic logging device to conductivity perturbations at various locations in the geological formation; generate a migration image of a target within the geological formation based on the calculated migration electromagnetic field, reference electromagnetic field, and integrated sensitivity; and determine the location, shape and electrical conductivity of the target based on the migration image. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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Specification