A method for surface estimation of reservoir properties, wherein location of and average earth resistivities above, below, and horizontally adjacent to the subsurface geologic formation are first determined using geological and geophysical data in the vicinity of the subsurface geologic formation. Then dimensions and probing frequency for an electromagnetic source are determined to substantially maximize transmitted vertical and horizontal electric currents at the subsurface geologic formation, using the location and the average earth resistivities. Next, the electromagnetic source is activated at or near surface, approximately centered above the subsurface geologic formation and a plurality of components of electromagnetic response is measured with a receiver array. Geometrical and electrical parameter constraints are determined, using the geological and geophysical data. Finally, the electromagnetic response is processed using the geometrical and electrical parameter constraints to produce inverted vertical and horizontal resistivity depth images. Optionally, the inverted resistivity depth images may be combined with the geological and geophysical data to estimate the reservoir fluid and shaliness properties.
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0. 49. A method for surface estimation of a resistivity depth image of a subsurface geological formation, comprising the steps of:
obtaining an electromagnetic source whose dimensions and probing frequency were determined to substantially maximize transmitted vertical and horizontal electric currents at the subsurface formation using a location of and at least one average earth resistivity for the vicinity of the formation, said location and average resistivity having been determined from geological and geophysical data from the vicinity of the formation;
activating the electromagnetic source at or near the surface of the earth, approximately centered above the subsurface geologic formation;
measuring a plurality of components of electromagnetic response with a receiver array; and
sending the electromagnetic response data to be processed, using one or more geometrical and electrical parameter constraints determined from the geological and geophysical data, to produce the resistivity depth image.
33. A method for surface estimation of one or more properties of a subsurface geologic formation, comprising the steps of:
determining the location of and at least one average earth resistivity for the vicinity of the subsurface geologic formation;
determining dimensions and probing frequency for an electromagnetic source to substantially maximize transmitted vertical electric currents at the subsurface geologic formation using the location and the at least one average earth resistivity;
activating the electromagnetic source at or near the surface of the earth, approximately centered above the subsurface geologic formation;
measuring at least a vertical electromagnetic response with a receiver array;
determining one or more geometrical and electrical parameter constraints, using geological and geophysical data from the vicinity of the subsurface geologic formation;
processing the electromagnetic response using the geometrical and electrical parameter constraints to estimate the one or more properties.
1. A method for surface estimation of a resistivity depth image of a subsurface geologic formation, comprising the steps of:
determining the location of and at least one average earth resistivity for the vicinity of the subsurface geologic formation using geological and geophysical data from the vicinity of the subsurface geologic formation;
determining dimensions and probing frequency for an electromagnetic source to substantially maximize transmitted vertical and horizontal electric currents at the subsurface geologic formation using the location and the at least one average earth resistivity;
activating the electromagnetic source at or near the surface of the earth, approximately centered above the subsurface geologic formation;
measuring a plurality of components of electromagnetic response with a receiver array;
determining one or more geometrical and electrical parameter constraints, using the geological and geophysical data; and
processing the electromagnetic response using the geometrical and electrical parameter constraints to produce the resistivity depth image.
0. 34. A method for surface estimation of a resistivity depth image of a subsurface geologic formation, said method comprising the steps of:
obtaining electromagnetic data, said data consisting of measurements previously made with a receiver array of a plurality of electromagnetic field components produced by a focused electromagnetic source located at or near the surface of the earth and approximately centered above the geologic formation, said focused electromagnetic source having been designed by determining the location of and at least one average earth resistivity for the vicinity of the subsurface geologic formation using geological and geophysical data from the vicinity of the subsurface geologic formation, and then determining dimensions and probing frequency for the electromagnetic source to substantially maximize transmitted vertical and horizontal electric currents at the subsurface geologic formation using the location of and the at least one average earth resistivity;
determining one or more geometrical and electrical parameter constraints, using geological and geophysical data from the vicinity of the subsurface geologic formation; and
processing the electromagnetic field measurements using the geometrical and electrical parameter constraints to produce the resistivity depth image.
31. A method for surface estimation of an inverted resistivity depth image of a subsurface geologic formation, comprising the steps of:
determining the location of and average earth resistivity above, below, and horizontally adjacent to the subsurface geologic formation using geological and geophysical data from the vicinity of the subsurface geologic formation;
determining dimensions and probing frequency for an electromagnetic source to substantially maximize transmitted vertical and horizontal electric currents at the subsurface geologic formation using the location and the at least one average earth resistivity, said source comprising six or more grounded linear radial electrodes of equal lengths placed along radii separated by equal angles whose radial projections intersect at a common central point, continuously grounded linear terminating electrodes connected substantially orthogonally at each end of the grounded radial electrodes;
activating the electromagnetic source at or near the surface of the earth, approximately centered above the subsurface geologic formation;
measuring a plurality of components of electromagnetic response with a receiver array;
determining one or more geometrical and electrical parameter constraints, using the geological and geophysical data; and
processing the electromagnetic response using the geometrical and electrical parameter constraints to produce the inverted resistivity depth image.
32. A method for surface estimation of one or more properties of a subsurface geologic formation, comprising the steps of:
determining the location of and at least one average earth resistivity for the vicinity of the subsurface geologic formation using geological and geophysical data from the vicinity of the subsurface geologic formation;
determining dimensions and probing frequency for an electromagnetic source to substantially maximize transmitted vertical and horizontal electric currents at the subsurface geologic formation using the location and the at least one average earth resistivity, said source comprising six or more grounded linear radial electrodes of equal lengths placed along radii separated by equal angles whose radial projections intersect at a common central point;
activating the electromagnetic source at or near the surface of the earth, approximately centered above the subsurface geologic formation;
measuring a plurality of components of electromagnetic response with a receiver array;
determining one or more geometrical and electrical parameter constraints, using the geological and geophysical data;
processing the electromagnetic response using the geometrical and electrical parameter constrains to produce one or more inverted resistivity depth images of the subsurface geologic formation; and
combining the inverted resistivity depth images with the geological and geophysical data to estimate the properties.
2. The method of
combining the resistivity depth image with the geological and geophysical data to estimate one or more properties of the subsurface geological formation.
3. The method of
4. The method of
two continuously grounded circular electrodes positioned in concentric circles.
5. The method of
6. The method of
a third circular electrode positioned concentric with the two circular electrodes.
7. The method of
8. The method of
9. The method of
10. The method of
12. The method of
16. The method of
verifying the at least one average earth resistivity using the plurality of components of electromagnetic response measured with the receiver array.
17. The method of
applying 3-D wave-equation data processing to the electromagnetic response.
18. The method of
19. The method of
measuring a first electromagnetic response without activating the electromagnetic source;
measuring a second electromagnetic response while activating only the third circular electrode; and
measuring a third electromagnetic response while activating only the two continuously grounded circular electrodes.
20. The method of
merging the first and second electromagnetic responses to produce a fourth electromagnetic response;
inverting the fourth electromagnetic response; and
inverting jointly the third and fourth electromagnetic responses.
21. The method of
inverting the first electromagnetic response;
inverting the second electromagnetic response; and
inverting the third electromagnetic response.
22. The method of
23. The method of
24. The method of
25. The method of
26. The method of
27. The method of
two orthogonal horizontal electric fields;
two orthogonal horizontal magnetic fields; and
a vertical magnetic field.
28. The method of
29. The method of
two orthogonal horizontal electric fields;
two orthogonal horizontal magnetic fields;
and a vertical electric field.
30. The method of
0. 35. The method of
0. 36. The method of
0. 37. The method of
0. 38. The method of
0. 39. The method of
0. 40. The method of
0. 41. The method of
0. 42. The method of
0. 43. The method of
0. 44. The method of
0. 45. The method of
0. 46. The method of
0. 47. The method of
measuring a first electromagnetic response without activating the electromagnetic source;
measuring a second electromagnetic response while activating only the third circular electrode; and
measuring a third electromagnetic response while activating only the two continuously grounded circular electrodes;
and wherein the processing step further comprises:
merging the first and second electromagnetic responses to produce a fourth electromagnetic response;
inverting the fourth electromagnetic response; and
inverting jointly the third and fourth electromagnetic responses.
0. 48. The method of
inverting the first electromagnetic response;
inverting the second electromagnetic response; and
inverting the third electromagnetic response.
0. 50. The method of
0. 51. The method of
0. 52. The method of
0. 53. The method of
0. 54. The method of
0. 55. The method of
measuring a first electromagnetic response without activating the electromagnetic source;
measuring a second electromagnetic response while activating only the third circular electrode; and
measuring a third electromagnetic response while activating only the two continuously grounded circular electrodes.
0. 56. The method of
0. 57. The method of
0. 58. The method of
0. 59. The method of
0. 60. The method of
0. 61. The method of
0. 62. The method of
0. 63. The method of
0. 64. The method of
two orthogonal horizontal electric fields;
two orthogonal horizontal magnetic fields; and
a vertical magnetic field.
0. 65. The method of
0. 66. The method of
two orthogonal horizontal electric fields;
two orthogonal horizontal magnetic fields; and
a vertical electric field.
0. 67. The method of
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This application
1/ρhoriz=(1/ρss)×ntg+(1/ρsh)×(1−ntg) (2)
Equations (1) and (2) contain three unknown averaged reservoir parameters: ρss, ρsh, and ntg. Estimates of ρsh within the reservoir interval, derived independently from the facies model or available facies data, are used next to derive and map the two remaining unknown values ρss and ntg over the spatial extent of the reservoir. Reservoir fluid type, hydrocarbon pore volume or water saturation are then derived from the mapped ρss value within the area of the seismically defined reservoir. Statistical methods including Monte Carlo inversions may also be used for deriving hydrocarbon pore volume, net-to-gross, water saturation, and other reservoir properties from the ρvert and ρhoriz inversion measurements. The derivation uses the facies model of rock properties distributions combined with Archie's Equations for the electrical resistivity of a porous rock containing fluid in the pore spaces, relative to ρss values within the same geologic unit outside of the reservoir.
The invention described above is designed to provide an order of magnitude improvement in subsurface vertical electromagnetic resolution over current technology.
The following example illustrates the application of the invention for onshore (land) hydrocarbon reservoir resistivity mapping. After 3-D seismic data in the survey area are acquired, interpreted, and converted to the depth domain, the prospective reservoir is identified (depth d and extent 1). Knowledge of the earth's electrical resistivity for the survey area, averaged over intervals of 0.10×d, from the earth's surface to three times the reservoir depth (3×d) and five times the reservoir extent (5×1), is gathered using existing electromagnetic survey data and well logs, or is estimated using geologic basin analogs. The diameters of the grounded electrodes are calculated by numerically solving the uninsulated buried low-frequency electromagnetic antenna problem as discussed above, or by iterated 3D electromagnetic modeling, using the reservoir depth and vertically averaged layered-earth resistivities as inputs. The diameter of the optional insulated loop electrode is determined using standard methods known in the art.
A preferred procedure is to obtain substantially optimal parameter values to substantially maximize the electric filed at the reservoir depth. However, as an alternative procedure, a sub-optimal aspect ratio b/a could be used to reduce electrode cost, installation effort, and survey permitting. For instance, an aspect ratio b/a=4 could be used. Use of this value for b/a would result in a 24.5% reduction in vertical electric field at the reservoir target, as shown in
Assume a vertically averaged resistivity of the earth of value ρe=1 Ohm-m. Then the central operating frequency of the grounded electrode array is derived from d/δ=9/4 and d=2250 meters, or f=0.050 Hz. The output bandwidth of the grounded electrode sources is 0.005≦f≦5.0 Hz. Using the analysis of B. R. Spies (1989, op. cit.), the central operating frequency of the insulated loop source is set by d/δ=1, or f=0.253 Hz. The output bandwidth of the insulated loop source is 0.025≦f≦25 Hz.
Nine power sources/controllers 7 are placed at the surface of the earth 1. Each source/controller is powered by connection to a municipal power grid, if available, or is powered by one or more generators in the field survey area. Each source/controller is nominally rated at 300 kVA, with outputs of 120 VAC and 2500 A (rms). One source/controller is situated at any position along the circumference of the insulated loop source 6, and is connected by a coaxial power cable 9 at the surface of the earth to the insulated loop source. The remaining eight power sources/controllers 7 are placed within a distance of L/10 of the midpoints of the partially grounded electrodes, as shown in FIG. 2. These eight power sources/controllers are connected to the grounded electrodes by means of coaxial or single-conductor power cables 8. The satellite Global Positioning System (GPS) signal is used to monitor and synchronize the phases of all the sources. Alternatively, if the number of power sources/controllers 7 is limited, or if survey logistics or terrain difficulties make simultaneous use of the eight radial grounded electrode positions impractical or too costly, one or more power sources/controller may be used to energize separately the eight partially grounded and the insulated loop source, in any sequential order.
The partially grounded electrodes 11 and the terminating electrodes 12 each consist of three uninsulated size 4/0 multi-strand copper wires. The grounded wires that comprise the grounded portion of each partially grounded electrode element 11 are buried in parallel within the top 1.0 meter of the earth's surface by means of manual digging or standard mechanical cable-laying devices. The ungrounded portions of each of the radial partially grounded electrodes 11 consist of three uninsulated size 4/0 multi-strand copper wires that are connected to the uninsulated buried electrode wires comprising the grounded portions. The ungrounded portions of each radial electrode are laid on the surface of the earth. Electrical contact of the grounded radial electrodes and the terminating electrodes is maintained with the earth by periodically wetting the buried electrode areas with water, as needed according to local ground moisture conditions. The loop source 6 consists of one single-conductor multi-strand insulated size 4/0 copper wire. Power connection cables 8 and 9 are electrically rated according to U.S. NEMA (National Electrical Manufacturing Association) codes and standards to carry the current delivered to the grounded electrodes 11,12 and to the insulated loop 6, respectively.
Electromagnetic receivers 10, such as Electromagnetic Instruments, Inc. (EMI) type MT-24/NS™ or equivalent, are positioned over the surface of the earth 1 within a radial distance r=(x2+y2)1/2=5000 meters from the center of the array, but not within 25 meters of any grounded electrode 11, 12 or the insulated loop 6, to minimize source-generated noise and saturation of the receiver signals. The receivers are positioned on a uniform grid as shown in
The five-component receivers are deployed simultaneously in large groups (16 or more) within the survey area, with as many receiver groups deployed as possible and practical for the local conditions of the survey (e.g. terrain difficulties, logistical support). Data are gathered for each receiver group by a central processing unit (EMI type FAM/CSU™ or equivalent). Differential GPS geodetic methods are used to measure the positions (x, y, z) of all receivers to within 0.1 meters accuracy. The GPS signal is also used for phase synchronization (timing) of all receiver data.
The receiver data are collected in three ways. First, the receiver data are collected as time records with all sources 7 turned off, to record zero excitation currents. These data are collected over a length of time that is sufficient to record raw stacked magnetotelluric data having three-sigma errors less than or equal to 5% over the frequency range 0.0025≦f≦25 Hz. Typically, collection of this data will take 1-10 days, depending upon local conditions and the logistics of receiver deployment. This first set of receiver data is magnetotelluric data. Second, the insulated loop source is energized using a standard electromagnetic industry bipolar square wave current from its attached power source/controller 7, as shown in FIG. 7. In this preferred embodiment of the method of the present invention, current pulse on-time, T1 equals current waveform off-time, T2, that is, T1=T2, but this is not a limitation of the method. Other source current waveforms may also be used for the insulated loop source current, including sinusoidal waveform combinations and pseudo-random sequences as well known to one skilled in the art, provided the insulated loop source frequency range is as stated. The receiver responses are collected using time-domain measurements acquired during the current waveform off-time, T2 in FIG. 7. The duration of the current pulse on-time, T1 in
The three sets of receiver data are processed in the following way. After noise suppression using standard industry methods as described above, the second set of vertical magnetic dipole data and the third set of grounded radial electrode measurements are converted to the complex frequency-wavenumber domain using standard industry 2-D Fourier and Radon transform techniques. The first set of magnetotelluric data and the second set of vertical magnetic dipole data are merged together in the frequency-wavenumber domain, for each electromagnetic tensor component of the data. The merged magnetotelluric and vertical magnetic dipole data sets are inverted, and the grounded radial electrode data set is inverted separately. Then the merged magnetotelluric and vertical magnetic dipole data and the grounded radial electrode data are inverted jointly, as discussed in D. Jupp and K. Vozoff, Geophys. Prospecting, v. 25, 460-470, 1977. The magnetotelluric data, the vertical magnetic dipole data, and the grounded radial electrode data are also inverted separately. All data inversions use the 3-D frequency-domain finite-difference fully nonlinear methods of G. A. Newman and D. L. Alumbaugh (1996, 1997, op. cit.), modified to allow for the geometries of the grounded radial electrode and the insulated loop source current arrays. Depth and parameter value constraints are enforced during the inversion, using sharp-boundary methods (G. Hoversten et al, 1998, op. cit.) and integral resistance and conductance bounds within the update region of the nonlinear inversion 3-D mesh that contains the reservoir target, combined with minimum-gradient support techniques (O. Portniaguine and M. Zhdanov, 1998, op. cit.). The nonlinear inversion update region is centered on the target reservoir, and extends 100 meters above and below the reservoir and 200 meters laterally from each reservoir edge.
The starting model for both the merged magnetotelluric and vertical magnetic dipole data inversion and the grounded radial electrode data inversion is an interpreted seismic depth model in which the mechanical properties (primarily the interval acoustic impedances) are replaced with resistivity estimates. The resistivity estimates may come from electromagnetic survey data, well logs, empirical relations to seismic parameters, or geologic basin analogs, as described above. The inversions are performed by means of a digital electronic computer of the massively parallel processor (MPP) type, or alternatively using a network of electronic digital computers that mimic an MPP computer. After the separate magnetotelluric, vertical magnetic dipole, and grounded radial electrode data inversions are completed, the magnetotelluric—vertical magnetic dipole and grounded radial electrode data are inverted jointly. The five respective 3-D depth cubes of inverted resistivity (magnetotelluric, vertical magnetic dipole, grounded radial electrode, merged magnetotelluric—vertical magnetic dipole, and merged magnetotelluric—vertical magnetic dipole—grounded radial electrode) are compared, and the ratios of their resistivity values are formed at each depth location using 3D visualization method. Finally, values of ρss, ρsh, and ntg are derived for the reservoir interval using the methods described above, and are mapped. These mapped values are interpreted in conjunction with the 3-D seismic data and its attributes.
The benefits provided by this invention include at least the following two. The first benefit is cost and cycle-time reduction in hydrocarbon exploration, development, and production activities, including reducing exploration drill-well risk, improving discovered-undeveloped reservoir delineation and assessment, and improving reservoir monitoring and depletion. The second benefit is improved business capture of new exploration ventures and field commercializations by offering unique, proprietary reservoir properties estimation technology.
It should be understood that the invention is not to be unduly limited to the foregoing which has been set forth for illustrative purposes. Various modifications and alternatives will be apparent to those skilled in the art without departing from the true scope of the invention, as defined in the following claims.
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