Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Exploring for structural traps

  | chapter = Exploring for structural traps

  | frompg  = 20-1

  | frompg  = 20-48

  | topg    = 20-70

  | topg    = 20-59

  | author  = R.A. Nelson, T.L. Patton, S. Serra

  | author  = R.A. Nelson, T.L. Patton, S. Serra

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch20/ch20.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch20/ch20.htm

==Tectonic setting==

==Tectonic setting==

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exploring-for-structural-traps_fig20-4.png|{{figure number|1}}See text for explanation.

exploring-for-structural-traps_fig20-4.png|{{figure number|1}}Structural exploration in the Laramide western Wyoming thrust belt in the late 1970s and early 1980s.

exploring-for-structural-traps_fig20-5.png|{{figure number|2}}From Schwartz<ref name=Schwartz_1982>Schwartz, R. T., 1982 Broken early cretaceous foreland basin in SW Montana: Sedimentation related to tectonism, ''in'' R. B. Powers, ed., Geological studies of the Cordilleran thrust belt: Rocky Mountain Association of Geologists, p. 159-183.</ref>; courtesy Rocky Mountain Association of Geologists.

exploring-for-structural-traps_fig20-5.png|{{figure number|2}}Tectonic setting for the western U.S. relevant to Laramide plate tectonics. From Schwartz<ref name=Schwartz_1982>Schwartz, R. T., 1982 Broken early cretaceous foreland basin in SW Montana: Sedimentation related to tectonism, ''in'' R. B. Powers, ed., Geological studies of the Cordilleran thrust belt: Rocky Mountain Association of Geologists, p. 159-183.</ref>; courtesy Rocky Mountain Association of Geologists.

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==Structural domains==

==Structural domains==

[[file:exploring-for-structural-traps_fig20-6.jpg|thumb|300px|{{figure number|3}}See text for explanation.]]

[[file:exploring-for-structural-traps_fig20-6.jpg|thumb|300px|{{figure number|3}}Satellite image.]]

==Prospective structural fairways==

==Prospective structural fairways==

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exploring-for-structural-traps_fig20-7.png|{{figure number|4}}From Dixon<ref name=Dixon_1982>Dixon, J. S., 1982, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0066/0010/1550/1560.htm Regional structural synthesis, Wyoming salient of the Western overthrust belt]: AAPG Bulletin, v. 66, p. 1560-1580. ''Maps and sections.''</ref>.

exploring-for-structural-traps_fig20-7.png|{{figure number|4}}Satellite image showing the location of the major thrust sheets in the Wyoming thrust belt. From Dixon<ref name=Dixon_1982>Dixon, J. S., 1982, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0066/0010/1550/1560.htm Regional structural synthesis, Wyoming salient of the Western overthrust belt]: AAPG Bulletin, v. 66, p. 1560-1580. ''Maps and sections.''</ref>.

exploring-for-structural-traps_fig20-8.png|{{figure number|5}}From Dixon<ref name=Dixon_1982 /> and Bishop<ref name=Bishop_1982>Bishop, R. A., 1982, Whitney Canyon-Carter Creek gas field, SW Wyoming, ''in'' R. B. Powers, ed., Geological studies of the Cordilleran thrust belt: Rocky Mountain Association of Geologists, p. 591-599.</ref>; courtesy AAPG and Rocky Mountain Association of Geologists, respectively.

exploring-for-structural-traps_fig20-8.png|{{figure number|5}}Contoured fault-plane map at two different scales for the Absaroka thrust, the major thrust that contains the producing fairway. From Dixon<ref name=Dixon_1982 /> and Bishop<ref name=Bishop_1982>Bishop, R. A., 1982, Whitney Canyon-Carter Creek gas field, SW Wyoming, ''in'' R. B. Powers, ed., Geological studies of the Cordilleran thrust belt: Rocky Mountain Association of Geologists, p. 591-599.</ref>; courtesy AAPG and Rocky Mountain Association of Geologists, respectively.

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Within the structural domains, regional analysis of structural style and timing were integrated with other elements of the hydrocarbon system to define prospective fairways. [[:file:exploring-for-structural-traps_fig20-7.png|Figure 4]] covers approximately the same area as the preceding satellite image and shows the location of the major thrust sheets in the Wyoming thrust belt. Note that most of the oil and gas fields occur in the southern half of the Absaroka thrust sheet.

Within the structural domains, regional analysis of structural style and timing were integrated with other elements of the hydrocarbon system to define prospective fairways. [[:file:exploring-for-structural-traps_fig20-7.png|Figure 4]] covers approximately the same area as the preceding satellite image and shows the location of the major thrust sheets in the Wyoming thrust belt. Note that most of the oil and gas fields occur in the southern half of the Absaroka thrust sheet.

[[:file:exploring-for-structural-traps_fig20-8.png|Figure 5]] is a contoured fault-plane map at two different scales for the Absaroka thrust, the major thrust that contains the producing fairway.

[[:file:exploring-for-structural-traps_fig20-8.png|Figure 5]] is a [[contour]]ed fault-plane map at two different scales for the Absaroka thrust, the major thrust that contains the producing fairway.

==Structural lead==

==Structural lead==

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file:exploring-for-structural-traps_fig20-9.png|{{figure number|6}}See text for explanation.

file:exploring-for-structural-traps_fig20-9.png|{{figure number|6}}Interpreted seismic line in the approximate location of [[:file:exploring-for-structural-traps_fig20-11.png|Figure 8]].

file:exploring-for-structural-traps_fig20-10.png|{{figure number|7}}From Sieverding and Royse<ref name=Sieverdingandroyse_1993>Sieverding, J. L., and F. Royse Jr., 1993, [http://archives.datapages.com/data/specpubs/fieldst3/data/a017/a017/0001/0000/0001.htm Whitney Canyon-Carter Creek Field-USA], ''in'' E. A. Beaumont and N. H. Foster, eds., Treatise of Petroleum Geology, Atlas of Oil and Gas Fields, Structural Traps III: AAPG, p. 1-29.</ref>.

file:exploring-for-structural-traps_fig20-10.png|{{figure number|7}}Restoration and balancing of a cross section through the Whitney Canyon and Ryckman Creek fields. From Sieverding and Royse<ref name=Sieverdingandroyse_1993>Sieverding, J. L., and F. Royse Jr., 1993, [http://archives.datapages.com/data/specpubs/fieldst3/data/a017/a017/0001/0000/0001.htm Whitney Canyon-Carter Creek Field-USA], ''in'' E. A. Beaumont and N. H. Foster, eds., Treatise of Petroleum Geology, Atlas of Oil and Gas Fields, Structural Traps III: AAPG, p. 1-29.</ref>.

file:exploring-for-structural-traps_fig20-11.png|{{figure number|8}}From Lamerson<ref name=Lamerson_1982>Lamerson, P. R., 1982, Fossil basin area and its relationship to the Absaroka thrust fault system, ''in'' R. B. Powers, ed., Geological studies of the Cordilleran thrust belt: Rocky Mountain Association of Geologists, p. 279-340.</ref>; courtesy Rocky Mountain Association of Geologists.

file:exploring-for-structural-traps_fig20-11.png|{{figure number|8}}Cross section across the Whitney Canyon and Ryckman Creek producing structures in the upper plate of the Absaroka thrust. From Lamerson<ref name=Lamerson_1982>Lamerson, P. R., 1982, Fossil basin area and its relationship to the Absaroka thrust fault system, ''in'' R. B. Powers, ed., Geological studies of the Cordilleran thrust belt: Rocky Mountain Association of Geologists, p. 279-340.</ref>; courtesy Rocky Mountain Association of Geologists.

file:exploring-for-structural-traps_fig20-12.png|{{figure number|9}}See text for explanation.

file:exploring-for-structural-traps_fig20-12.png|{{figure number|9}}Structures in the upper plate of the Absaroka thrust in the central Wyoming thrust belt, updip and along strike of the producing structures in the same thrust sheet to the south.

file:exploring-for-structural-traps_fig20-13.png|{{figure number|10}}See text for explanation.

file:exploring-for-structural-traps_fig20-13.png|{{figure number|10}}Structures in the upper plate of the Absaroka thrust fault on the south side of ridge line 4 in [[:file:exploring-for-structural-traps_fig20-12.png|Figure 9]]. The white outcrops in the valley in the left foreground are tightly folded Ordovician Bighorn dolomite.

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Detailed analysis of the fairway proceeded using surface and subsurface data. Examples of the data used are shown below.

Detailed analysis of the fairway proceeded using surface and subsurface data. Examples of the data used are shown below.

[[:file:exploring-for-structural-traps_fig20-11.png|Figure 8]] shows a cross section across the Whitney Canyon and Ryckman Creek producing structures in the upper plate of the Absaroka thrust.

[[:file:exploring-for-structural-traps_fig20-11.png|Figure 8]] shows a [[cross section]] across the Whitney Canyon and Ryckman Creek producing structures in the upper plate of the Absaroka thrust.

[[:file:exploring-for-structural-traps_fig20-9.png|Figure 6]] shows an interpreted seismic line in the approximate location of [[:file:exploring-for-structural-traps_fig20-11.png|Figure 8]].

[[:file:exploring-for-structural-traps_fig20-9.png|Figure 6]] shows an interpreted seismic line in the approximate location of [[:file:exploring-for-structural-traps_fig20-11.png|Figure 8]].

The oblique aerial photograph in [[:file:exploring-for-structural-traps_fig20-12.png|Figure 9]] shows structures in the upper plate of the Absaroka thrust in the central Wyoming thrust belt, updip and along strike of the producing structures in the same thrust sheet to the south. (See [[:file:exploring-for-structural-traps_fig20-6.jpg|Figure 3]] for the location.)

The oblique aerial photograph in [[:file:exploring-for-structural-traps_fig20-12.png|Figure 9]] shows structures in the upper plate of the Absaroka thrust in the central Wyoming thrust belt, updip and along strike of the producing structures in the same thrust sheet to the south. (See [[:file:exploring-for-structural-traps_fig20-6.jpg|Figure 3]] for the location.)

The tectonic setting and stratigraphic section are similar to the producing trend; therefore, the deformation features of the exposed structures can be used as analogs for producing structures to the south. The numbered ridge lines in the photo provide a set of natural serial cross sections through the structures ([[:file:exploring-for-structural-traps_fig20-13.png|Figure 10]]).

The tectonic setting and stratigraphic section are similar to the producing trend; therefore, the [[deformation]] features of the exposed structures can be used as analogs for producing structures to the south. The numbered ridge lines in the photo provide a set of natural serial cross sections through the structures ([[:file:exploring-for-structural-traps_fig20-13.png|Figure 10]]).

[[:file:exploring-for-structural-traps_fig20-14.png|Figure 10]] shows structures in the upper plate of the Absaroka thrust fault on the south side of ridge line 4 in [[:file:exploring-for-structural-traps_fig20-12.png|Figure 9]]. The white outcrops in the valley in the left foreground are tightly folded Ordovician Bighorn dolomite.

[[:file:exploring-for-structural-traps_fig20-14.png|Figure 10]] shows structures in the upper plate of the Absaroka thrust fault on the south side of ridge line 4 in [[:file:exploring-for-structural-traps_fig20-12.png|Figure 9]]. The white [http://www.merriam-webster.com/dictionary/outcrop outcrops] in the valley in the left foreground are tightly folded Ordovician Bighorn [[dolomite]].

==Prospect and location==

==Prospect and location==

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file:exploring-for-structural-traps_fig20-14.png|{{figure number|11}}See text for explanation.

file:exploring-for-structural-traps_fig20-14.png|{{figure number|11}}Photograph showing structures in the upper plate of the Absaroka thrust fault.

file:exploring-for-structural-traps_fig20-15.png|{{figure number|12}}From <ref name=Lamerson_1982 />; courtesy Rocky Mountain Association of Geologists.

file:exploring-for-structural-traps_fig20-15.png|{{figure number|12}}Example of detailed structural mapping at the prospect level. From Lamerson;<ref name=Lamerson_1982 /> courtesy Rocky Mountain Association of Geologists.

file:exploring-for-structural-traps_fig20-16.jpg|{{figure number|13}}Published with permission of James Morse, Computational Geology.

file:exploring-for-structural-traps_fig20-16.jpg|{{figure number|13}}Physical models display structures similar in shape to natural, prospect-scale, thrust-related structures can provide insight on the overall geometry of the prospect and the location of zones of high strain (high fracture density?) within the structure. Published with permission of James Morse, Computational Geology.

file:exploring-for-structural-traps_fig20-17.png|{{figure number|14}}See text for explanation.

file:exploring-for-structural-traps_fig20-17.png|{{figure number|14}}Examples of outcrop fracture-spacing data relevant to the carbonate section of Whitney Canyon field

file:exploring-for-structural-traps_fig20-18.png|{{figure number|15}}From Nelson and Serra<ref name=Nelsonandserra_1995>Nelson, R. A., and S. Serra, 1995, Vertical and lateral changes in fracture spacing in several folded carbonate sections and its relation to locating horizontal wells: Journal of Canadian Petroleum Technology, v. 34, p. 51-56.</ref>; courtesy Journal of Canadian Petroleum Technology.

file:exploring-for-structural-traps_fig20-18.png|{{figure number|15}}Outcrop sketch of folds in the Devonian Darby siltstone and Ordovician Bighorn dolomite. From Nelson and Serra<ref name=Nelsonandserra_1995>Nelson, R. A., and S. Serra, 1995, Vertical and lateral changes in fracture spacing in several folded carbonate sections and its relation to locating horizontal wells: Journal of Canadian Petroleum Technology, v. 34, p. 51-56.</ref>; courtesy Journal of Canadian Petroleum Technology.

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Once leads have been defined, detailed analyses of individual well locations must take place. [[:file:exploring-for-structural-traps_fig20-15.png|Figure 12]] shows an example of detailed structural mapping at the prospect level. It is a structural map on top of the Upper Triassic Nugget Sandstone, Ryckman Creek field area, Uinta County, Wyoming. Contour interval varies from [[length::100 ft]] (30 m) near the crest of the structure to [[length::500 ft]] (150 m) on the flanks. The dashed contours are the oil/water and gas/oil contacts.

Once leads have been defined, detailed analyses of individual well locations must take place. [[:file:exploring-for-structural-traps_fig20-15.png|Figure 12]] shows an example of detailed structural mapping at the prospect level. It is a structural map on top of the Upper Triassic Nugget Sandstone, Ryckman Creek field area, Uinta County, Wyoming. [[Contour]] interval varies from [[length::100 ft]] (30 m) near the crest of the structure to [[length::500 ft]] (150 m) on the flanks. The dashed contours are the oil/water and gas/oil contacts.

Physical models, such as those in [[:file:exploring-for-structural-traps_fig20-16.jpg|Figure 13]], that display structures similar in shape to natural, prospect-scale, thrust-related structures can provide insight on the overall geometry of the prospect and the location of zones of high strain (high fracture density?) within the structure. These insights can be useful in determining optimal well locations.

Physical models, such as those in [[:file:exploring-for-structural-traps_fig20-16.jpg|Figure 13]], that display structures similar in shape to natural, prospect-scale, thrust-related structures can provide insight on the overall geometry of the prospect and the location of zones of high strain (high [[fracture]] density?) within the structure. These insights can be useful in determining optimal well locations.

These models were constructed of originally planar layers of limestone, sandstone, and granite. They were deformed in a pressure vessel at an effective overburden pressure of 15 × 10³ psi (1 × 10⁵ kPa). The top view is a photomicrograph of a model that simulates a thrust ramp. The bottom view simulates the hanging-wall geometry produced by movement along a series of bedding-parallel and ramp segments of a thrust fault.

These models were constructed of originally planar layers of [[limestone]], sandstone, and granite. They were [[Deformation|deformed]] in a pressure vessel at an effective overburden pressure of 15 × 10³ psi (1 × 10⁵ kPa). The top view is a photomicrograph of a model that simulates a thrust ramp. The bottom view simulates the hanging-wall geometry produced by movement along a series of bedding-parallel and ramp segments of a thrust fault.

Data on deformation mechanisms, such as fractures and how they affect reservoir properties, are obtained by integrating outcrop fracture data and laboratory estimates of fracture aperture. This integration allows for a direct calculation of fracture [[porosity]] and fracture [[permeability]] for the reservoir.

Data on deformation mechanisms, such as fractures and how they affect reservoir properties, are obtained by integrating [http://www.merriam-webster.com/dictionary/outcrop outcrop] fracture data and laboratory estimates of fracture aperture. This integration allows for a direct calculation of fracture [[porosity]] and fracture [[permeability]] for the reservoir.

Examples of outcrop fracture-spacing data relevant to the carbonate section of Whitney Canyon field are shown in [[:file:exploring-for-structural-traps_fig20-14.png|Figure 13]]. The photograph shows fractures in the Ordovician Bighorn dolomite in outcrops in the valley seen in [[:file:exploring-for-structural-traps_fig20-14.png|Figure 11]]. (Note the inch-scale measuring tape stretched across the center of [[:file:exploring-for-structural-traps_fig20-17.png|Figure 14]].)

Examples of outcrop fracture-spacing data relevant to the carbonate section of Whitney Canyon field are shown in [[:file:exploring-for-structural-traps_fig20-17.png|Figure 14]]. The photograph shows fractures in the Ordovician Bighorn dolomite in outcrops in the valley seen in [[:file:exploring-for-structural-traps_fig20-14.png|Figure 11]]. (Note the inch-scale measuring tape stretched across the center of [[:file:exploring-for-structural-traps_fig20-17.png|Figure 14]].)

The outcrop sketch in [[:file:exploring-for-structural-traps_fig20-18.png|Figure 15]] is of folds in the Devonian Darby siltstone and Ordovician Bighorn dolomite from the same location as [[:file:exploring-for-structural-traps_fig20-17.png|Figure 14]]. The numbers on the sketch represent fracture intensity values expressed as the average number of fractures encountered per foot of scanline measurement at various locations on the folds. All else being equal, higher fracture intensities should be associated with zones of higher fracture porosities and permeabilities. Maps of high fracture intensities can be used to locate optimum well locations and well trajectories in prospects.

The outcrop sketch in [[:file:exploring-for-structural-traps_fig20-18.png|Figure 15]] is of folds in the Devonian Darby siltstone and Ordovician Bighorn dolomite from the same location as [[:file:exploring-for-structural-traps_fig20-17.png|Figure 14]]. The numbers on the sketch represent fracture intensity values expressed as the average number of fractures encountered per foot of scanline measurement at various locations on the folds. All else being equal, higher fracture intensities should be associated with zones of higher fracture porosities and permeabilities. Maps of high fracture intensities can be used to locate optimum well locations and well trajectories in prospects.

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Exploring for structural traps]]

[[Category:Exploring for structural traps]]