Seismic surveying technique for the detection of azimuthal variations in the earth's subsurface
AssigneeAmoco Corporation
InventorsRichard M. Alford, Heloise B. Lynn, Leon A. Thomsen
Life of this patent
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Abstract
Polarized shear wave surveys are performed to determine azimuthal variations in the earth's subsurface caused by fracture orientation and density. The surveys may be done by using the same polarization (either horizontal or vertical) shear waves along two different seismic lines of profile, or by using different polarization shear waves along one common line of profile. The survey data are then processed and compared; any differences constitute a measure of fracture orientation and density. Subsurface zones of high fracture density, once identified, have been found to afford a higher likelihood of successful well completion.
Claims50
A method of surveying the earth's subsurface formations to determine azimuthal variations in the earth's subsurface comprising the steps of:
- (a) imparting shear wave seismic energy into the earth with a first seismic source polarized in a first direction along a first seismic line of profile;
- (b) recording the reflected shear wave seismic energy with a first geophone having a polarization matching the polarization of the first seismic source to produce a first shear wave record;
- (c) imparting shear wave seismic energy into the earth with a second seismic source polarized in a second direction along a second seismic line of profile;
- (d) recording the reflected shear wave seismic energy with a second geophone having a polarization matching the polarization of the second seismic source to produce a second shear wave record;
- (e) processing the first and second shear wave records to produce a first and second shear wave section;
- and
- (f) comparing the first and second shear wave seismic sections to determine azimuthal variations in the earth's subsurface.
A method of surveying subsurface earth formations along two crossing seismic lines to investigate azimuthal variations in subsurface formations, comprising the steps of:
- (a) imparting shear wave seismic energy into the earth with a first seismic source polarized in a first direction at selected points along a first seismic line of profile;
- (b) recording the response of the earth formations to the shear wave seismic energy at selected points on the first seismic line of profile with a geophone having a polarization matching the polarization of the first seismic source;
- (c) imparting shear wave seismic energy into the earth with a second seismic source polarized in a second direction at selected points along a second seismic line of profile which crosses the first seismic line of profile;
- (d) recording the response of the earth formations to the shear wave seismic energy at selected points on the second seismic line of profile with a geophone having a polarization matching the polarization of the second seismic source;
- and
- (e) processing both recorded responses to form a sher wave seismic section for each of the first and second seismic lines of profile to determine the presence of fractures and their orientation and density in the subsurface formations.
A method of surveying subsurface earth formations along a single seismic line of profile to investigate azimuthal variations in the subsurface formations;
- comprising the steps of:
- (a) imparting shear wave seismic energy into the earth with a first seismic source polarized in a first direction at selected points along the seismic line of profile;
- (b) recording the response of the earth's formations to the shear wave seismic energy at selected points along the seismic line of profile with a geophone having a polarization matching the polarization of the first seismic source;
- (c) imparting shear wave seismic energy into the earth with a second seismic source polarized in a second direction at selected points along the seismic line of profile;
- (d) recording the response of the earth's formations to the shear wave seismic energy at selected points along the seismic line of profile with a geophone having a polarization matching the polarization of the second seismic source;
- and
- (e) processing the recorded response to produce two shear wave seismic sections along the seismic line of profile to determine the presence of fractures and their orientation and density in the formation.
A method for acquiring seismic data in locations having azimuthally anisotropic subsurface formations comprising the following steps:
- (a) imparting shear wave seismic energy into the earth with a first seismic source polarized in a first direction along a first seismic line of profile;
- (b) recording the earth's response to the imparted shear wave seismic energy with a first geophone having a polarization matching the polarization of the first seismic source to produce a first shear wave record;
- (c) imparting shear wave seismic energy into the earth with a second seismic source polarized in a second direction along a second seismic line of profile;
- and
- (d) recording the earth's response to the imparted shear wave seismic energy with a second geophone having a polarization matching the polarization of the first seismic source to produce a second shear wave record.
A method of surveying azimuthally subsurface earth formations along two crossing seismic lines of profile comprising the steps of:
- (a) imparting shear wave seismic energy into the earth with a first seismic source polarized in a first direction at selected points along a first seismic line of profile;
- (b) recording the response of the earth formations to the shear wave seismic energy at selected points on the first seismic line of profile with a geophone having a polarization matching the polarization of the first seismic source;
- (c) imparting shear wave seismic energy into the earth with a second seismic source polarized in a second direction at selected points along a second seismic line of profile which crosses the first seismic line of profile;
- and
- (d) recording the response of the earth formations to the shear wave seismic energy at selected points on the second seismic line of profile with a geophone having a polarization matching the polarization of the second seismic source.
A method of surveying azimuthally anisotropic subsurface earth formations along a single seismic line of profile comprising the steps of:
- (a) imparting shear wave seismic energy into the earth with a first seismic source polarized in the first direction at selected points along a seismic line of profile
- (b) recording the response of the earth's formations to the shear wave seismic energy at selected points along the seismic line of profile with a geophone having a polarization matching the polarization of the first seismic source;
- (c) imparting shear wave seismic energy into the earth with a second seismic source polarized in a second direction at selected points along the seismic line of profile;
- and
- (d) recording the response of the earth's formations to the shear wave seismic energy at selected points along the seismic line of profile with a geophone having a polarization matching the polarization of the second seismic source.
A method for determining azimuthal variations in the earth's subsurface comprising the steps of:
- (a) displaying a first record of shear wave seismic energy imparted into the earth by a shear wave seismic source polarized in a first direction along a first seismic line of profile and received by a first geophone havng a matched polarization;
- (b) displaying a second record of shear wave seismic energy imparted into the earth by a shear wave seismic source polarized in a second direction along a second seismic line of profile and received by a second geophone having a matched polarization;
- and
- (c) comparing the first and second records of shear wave seismic energy to determine azimuthal variations in the earth's subsurface.
A method for determining azimuthal variations in the earth's subsurface comprising the steps of:
- (a) displaying a first record of shear wave seismic energy imparted into the earth by a shear wave seismic source polarized in a first direction along a seismic line of profile and received by a first geophone having a matched polarization;
- (b) displaying a second record of shear wave seismic energy imparted into the earth by a shear wave seismic source polarized in a second direction along the seismic line of profile and received by a second geophone having a matched polarization;
- and
- (c) comparing the first and a second records of shear wave seismic energy to determine azimuthal variations in the earth's subsurface.
Dependencies are inferred from the claim text.