Patent Application
20160238704
The present invention relates generally to remote sensing of subterranean formations. More particularly, but not by way of limitation, embodiments of the present invention include tools and methods for assessing oil and gas reservoirs using radar interferometry.
Traditionally, oil and gas reservoirs have been characterized by using subsurface engineering methods. Improving oil and gas reservoir performance has relied on data obtained by subsurface methods that feature, for example, wellbore geomechanics, sonic logs, and seismic interpretation of subsurface reflectors. These subsurface methods often require delicate and expensive equipment collecting computationally intensive data. Currently, there are limited number of non-subsurface analytical methods that can independently, conveniently, and cost-effectively assess reservoirs for exploration, production, and/or containment evaluation purposes.
Radar interferometry or interferometric synthetic aperture radar (InSAR) is a specialized radar technique used to measure Earth's surface deformations remotely from above the Earth's surface (e.g., Bürgmann and Thatcher, 2013). InSAR uses phase interferometer methods between two spatially displaced high resolution synthetic aperture radar (SAR) images to generate high quality terrain elevation maps. Deformations small as centimeter-scale can be detected by comparing time-lapsed satellite SAR images. The satellite images may be taken, for example, a few days apart to a few years apart. Radar interferometry has been used primarily to monitor natural hazards such as earthquakes, volcanoes and landslides. Radar interferometry has seen some use in oil and gas applications such as production monitoring in heavy oil fields (Stancliffe and van der Wooij, 2001; Gu et al., 2011; Teatini et al., 2011; Khakim et al., 2012) but has not yet been fully realized for subsurface faults within oil and gas fields.
The present invention relates generally to remote sensing of subterranean formations. More particularly, but not by way of limitation, embodiments of the present invention include tools and methods for assessing oil and gas reservoirs using radar interferometry.
One example of a method for assessing an onshore hydrocarbon reservoir, includes: a) obtaining a plurality of synthetic aperture radar images of the Earth's surface; b) identifying and acquiring synthetic aperture radar images covering the onshore hydrocarbon reservoir; c) assessing technical characteristic of the radar images, the technical characteristic selected from the group consisting of: look direction, baseline, temporal coherence, correlation, degree and direction of overlap, spatial resolution, desired temporal coverage, and any combination thereof; d) constructing an interferogram showing ground motion over a selected time interval; e) determining one or more deformations of the Earth's surface, wherein the one or more deformations are near or on the onshore hydrocarbon reservoir; f) identifying a fault in the Earth's subsurface, wherein the fault provides leakage path for a subsurface fluid; g) interpreting magnitude and pattern of ground motion that indicate currently or recently active displacement along the fault at the Earth's surface; h) correlating interpreted magnitude and pattern of ground motion with independent surface or subsurface data; i) using the interferogram to identify currently or recently active fault to augment or test subsurface data and interpretation regarding reservoir performance; j) revising one or more operational parameters related to hydrocarbon recovery; and k) recovering the hydrocarbon from the leakage path by using drilling, completion, or reservoir engineering techniques.
Another example of a method for assessing an onshore reservoir, includes: a) obtaining synthetic aperture radar images covering at least a portion of the onshore reservoir; b) identifying one or more deformations of a selected area, wherein the one or more deformations are near or on the onshore reservoir; c) analyzing ground motions in the selected area to identify currently or recently active displacement along a fault on or near the onshore reservoir; d) comparing analyzed ground motions with independent surface or subsurface data; and e) revising one or more operational parameters related to subsurface fluid recovery.
Yet another example of a method for assessing an onshore hydrocarbon reservoir, includes: a) acquiring synthetic aperture radar images of the onshore hydrocarbon reservoir; b) constructing an interferogram based on the synthetic aperture radar images; c) determining one or more deformations of the Earth's surface from the interferogram, wherein the one or more deformations are near or on the onshore hydrocarbon reservoir; d) identifying a fault in the Earth's subsurface, wherein the fault provides leakage path for a subsurface fluid; e) interpreting magnitude and pattern of ground motion that indicate currently or recently active displacement along the fault at the Earth's surface; f) correlating interpreted magnitude and pattern of ground motion with independent surface or subsurface data; g) using the interferogram to identify currently or recently active fault to augment or test subsurface data and interpretation regarding reservoir performance; and h) revising one or more operational parameters related to hydrocarbon recovery.
A more complete understanding of the present invention and benefits thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings in which:
Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not as a limitation of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations that come within the scope of the invention.
One of the goals of the present invention is to extend the use of radar interferometry for oil and gas applications involving subsurface faults. While radar interferometry is a mature technique, it has not yet been fully realized for oil and gas applications involving subsurface faults. The present invention provides tools and methods for assessing oil and gas reservoirs by identifying active fault-related deformations in or near onshore oil and gas fields using radar interferometry. It is believed and becoming more widely recognized that a relationship exists between stress state, stress heterogeneity, and permeability of subsurface fractures and faults. In other words, these fault-related deformations can significantly alter geophysical properties of a reservoir, which in turn, can impact oil field strategies and decisions on how to locate and safely maximize retrieval of hydrocarbons.
Many oil and gas reservoirs are located in tectonically quiet continental interiors or in passive continental margins offshore. Other oil and gas reservoirs may be located onshore in or near tectonically active areas such as subduction zones where two tectonic plates come together, one riding over the other, causing one plate to sink into the mantle as the tectonic plates converge. Typically, rate of convergence can range from about 2 to 8 cm per year. A geological fault can compartmentalize oil and gas reservoir and its trapped hydrocarbon, providing a leakage path for subsurface fluids during, for example, production or wastewater disposal operations. Geological faults in tectonically active areas (such as near subduction zones) can be critically stressed, leading to increased productivity where wells intersect faults and damage zones. Radar interferometry can be particularly useful in identifying areas of enhanced reservoir performance and in guiding efforts to improve production.
As used herein, the term “critically stressed” refers to a fracture that is favorably oriented to fail in shear under a stress field. A critically stressed fracture may be inferred from a variety of factors including, but not limited to, wellbores, seismically-interpreted stratigraphic offsets, as well as other subsurface data. As used herein, “fault” is a plane of detachment (e.g., a fracture or discontinuity) in a volume of rock, across which there has been significant displacement along the plane of detachment resulting from earth movement. The term “deformation” refers to a change in shape or volume caused by applied stress.
As used herein, “damage zone” refers to volume of deformed wall rocks around a fault surface. Typically, damage zone results from initiation, propagation, interaction and build-up of slip along faults.
Radar interferometry (sometimes referred to as “interferometric synthetic aperture radar” or “InSAR” or “SAR”) is a well-known technique that uses multiple images (2 or more) to generate maps of surface deformation or digital terrain based on differences in phase of waves returning to a satellite or aircraft. Thus, SAR provides a remote sensing technology that produces accurate land surface elevation change measurements. Since SAR is based on sensing reflections of electromagnetic waves, the radar can be operated day and night and even through cloudy conditions. Radar interferometry can also be cost-effective especially when compared to conventional subsurface methods. Other advantages will be apparent from the disclosure herein.
In principle, an SAR system transmits an electromagnetic signal and measures magnitude and phase of the signal backscattered from the earth's surface. Magnitude is generally affected by properties of the surface. Phase is an indication of the distance between the SAR system and surface and surface scattering effect on the incident electromagnetic wave. Changes to the surface can be observed by taking a second SAR data set collected from the same or nearly same location in space as the first image and subtracting the phase of the second image from the first image, which generates an interferogram. This process can be used to monitor ground deformations associated with active faulting, ground water withdrawal and recharge, and volcano inflation and hazards. Moreover, extraction of oil can cause volume reduction or increase of the subsurface, which in turn is manifested by subsidence or uplift at surface.
In accordance with the present invention, radar interferometry can be used to identify occurrence of critically stressed or active faults in the subsurface to potentially identify areas of enhanced reservoir performance and guide efforts to improve production. A number of challenges have prevented the widespread use of radar interferometry in oil and gas industry involving subsurface faults. For one, radar interferometry in oil and gas applications has generally focused on reservoirs that are located in tectonically quiet continental interiors or in passive continental margins (e.g., Gu et al., 2011; Khakim et al., 2012). Furthermore, there is technical challenge of integrating or complementing radar interferometry data with subsurface data to, for example, locate potentially rich reservoirs, increase production, as well as address safety issues surrounding tectonically active areas.
In some embodiments, radar images can be assessed for technical characteristics. Examples of technical characteristic include, but are not limited to, look direction, baseline, temporal coherence, correlation, degree and direction of overlap, spatial resolution, desired temporal coverage, and any combination thereof;
The present invention extends the use of radar interferometry to oil and gas fields located in tectonically active areas and involving subsurface faults, which in turn can be used to provide novel and valuable insights that can be used to make oil field decisions related to exploration, production, and/or containment. Moreover, data obtained from radar interferometry may be compared with subsurface data to provide independent confirmation or to improve quality of reservoir assessment. Conventional subsurface methods typically do not provide time-lapsed deformation changes.
This Example describes an embodiment of the present invention as applied to an oil and gas producing field, Suban field located in Sumatra, Indonesia (e.g., Schultz et al., 2014a, b). Synthetic aperture radar data were obtained from the Advanced Land Observing Satellite (ALOS) via an L-band (23.6 cm wavelength) radar which provides good temporal coherence for constructing interferograms. Twenty-six obtained raw images (19 ascending and 7 descending acquisitions) were used to perform an interferometry analysis (e.g., Soofi and Sandwell, 2010; Tong et al., 2013).
During the interferometry analysis, raw binary radar images were pre-processed and focused to form full-resolution SAR images. All SAR images were aligned to a single image with 2D cross-correlation techniques. Typically, the image alignment needs to be accurate within ˜1 pixel (˜10 m) in order to construct the interferograms. During this process, phase due topography was removed and the residual phase was unwrapped (e.g., Chen and Zebker, 2000). These unwrapped phase maps were then individually filtered with a high-pass Gaussian filter and stacked to yield an average line-of-sight (LOS) velocity map (
The pattern of uplift rate across the bounding fault is consistent with the deformation of the ground surface above blind reverse or thrust faults in other contractional tectonic settings (e.g., King et al., 1988; Ma and Kusznir, 1993; Cohen, 1999; Okubo and Schultz, 2004; Schultz, 2011). The pattern of uplift generally correlates with contemporary topography as shown by SW to NE transect. The similarity of uplift and topography along the transect implies that the current topography across this part of Suban field is related at least in part to reverse offsets along the subjacent faults and related deformation. Results obtained from the method are consistent with inferences made by Hennings et al. (2012) on basis of wellbore and other subsurface data that the faults were active and related to subduction tectonics across Sumatra.
Referring to
In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as additional embodiments of the present invention.
Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.
All of the references cited herein are expressly incorporated by reference. The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication data after the priority date of this application. Incorporated references are listed again here for convenience:
Deformation Measurements of Tectonic Processes, in Bickford, M. E., ed., The Web of Geological Sciences: Advances, Impacts, and Interactions: Geological Society of America Special Paper 500, p. 397-430.
This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 62/081,945 filed Nov. 19, 2014, entitled “SATELLITE GEODESY AND RESERVOIR PERFORMANCE,” which is incorporated herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62081945 | Nov 2014 | US |
