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This example of structural exploration in the Laramide western Wyoming thrust belt in the late 1970s and early 1980s illustrates how the preceding tasks flow together and applies the techniques and approaches in Figure 20-4. The exploration process begins with an examination of the regional tectonic setting of the Wyoming thrust belt and gradually narrows to a study of structural features at the prospect level.

This example of structural exploration in the Laramide western Wyoming thrust belt in the late 1970s and early 1980s illustrates how the preceding tasks flow together and applies the techniques and approaches in [[Figure 20-4]]. The exploration process begins with an examination of the regional tectonic setting of the Wyoming thrust belt and gradually narrows to a study of structural features at the prospect level.

==Tectonic setting==

==Tectonic setting==

==Structural domains==

==Structural domains==

Structural domains within the Wyoming thrust belt were defined by the regional mapping of the U.S. Geological Survey<ref name=ch20r232>Rubey, W., W., 1973, Geologic map of the Afton quadrangle and part of the big Piney quadrangle, Lincoln and Sublette counties, Wyoming: U., S. Geological Survey map I–686.</ref> and by interpreting satellite images such as the one shown in [[:file:exploring-for-structural-traps_fig20-6.jpg|Figure 2]]. Individual major thrust sheets were defined across the belt as well as their change in character along strike, thus defining domains on a large scale. Note that the small white rectangle in the center of the satellite image is the approximate area seen in the oblique aerial photograph in [[file:exploring-for-structural-traps_fig20-12.png|Figure 8]].

Structural domains within the Wyoming thrust belt were defined by the regional mapping of the U.S. Geological Survey<ref name=ch20r232>Rubey, W., W., 1973, Geologic map of the Afton quadrangle and part of the big Piney quadrangle, Lincoln and Sublette counties, Wyoming: U., S. Geological Survey map I–686.</ref> and by interpreting satellite images such as the one shown in [[:file:exploring-for-structural-traps_fig20-6.jpg|Figure 2]]. Individual major thrust sheets were defined across the belt as well as their change in character along strike, thus defining domains on a large scale. Note that the small white rectangle in the center of the satellite image is the approximate area seen in the oblique aerial photograph in [[:file:exploring-for-structural-traps_fig20-12.png|Figure 8]].

==Prospective structural fairways==

==Prospective structural fairways==

==Prospect and location==

==Prospect and location==

Once leads have been defined, detailed analyses of individual well locations must take place. The figure below 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 11]] 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.

[[file:exploring-for-structural-traps_fig20-15.png|thumb|{{figure number|20-15}}. Copyright: Lamerson, 1982; courtesy Rocky Mountain Assoc. of Geologists.]]

[[file:exploring-for-structural-traps_fig20-15.png|thumb|{{figure number|11}}. Copyright: Lamerson, 1982; courtesy Rocky Mountain Assoc. of Geologists.]]

Physical models, such as those shown below, 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 12]], 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 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.

[[file:exploring-for-structural-traps_fig20-16.jpg|thumb|{{figure number|20-16}}Published with permission of James Morse, Computational Geology.]]

[[file:exploring-for-structural-traps_fig20-16.jpg|thumb|{{figure number|12}}Published with permission of James Morse, Computational Geology.]]

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 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 below. The photograph shows fractures in the Ordovician Bighorn dolomite in outcrops in the valley seen in Figure 20-14. (Note the inch-scale measuring tape stretched across the center of Figure 20-17.)

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 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 10]]. (Note the inch-scale measuring tape stretched across the center of Figure 20-17.)

[[file:exploring-for-structural-traps_fig20-17.png|thumb|{{figure number|20-17}}See text for explanation.]]

[[file:exploring-for-structural-traps_fig20-17.png|thumb|{{figure number|13}}See text for explanation.]]

The outcrop sketch below is of folds in the Devonian Darby siltstone and Ordovician Bighorn dolomite from the same location as Figure 20-17. 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 14]] 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 13]]. 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.

[[file:exploring-for-structural-traps_fig20-18.png|thumb|{{figure number|20-18}}. Copyright: Nelson and Serra, 1995; courtesy Journal of Canadian Petroleum Technology.]]

[[file:exploring-for-structural-traps_fig20-18.png|thumb|{{figure number|14}}. Copyright: Nelson and Serra, 1995; courtesy Journal of Canadian Petroleum Technology.]]

==Summary==

==Summary==