Changes

===Geologic Model Results===

===Geologic Model Results===

[[File:BLTN13190fig10.jpg|thumb|400px|{{figure number|10}}(A) Plan-view facies association map of the Ferron Sandstone Member extracted from our reservoir model ([[:File:BLTN13190fig5.jpg|Figure 5D]]), showing location of injector and producer wells, and the cross section illustrated in [[:File:BLTN13190fig10.jpg|Figure 10B–D]]. The color scheme is the same as in Figures 5D and 8A. (B) Depositional-dip-oriented cross section showing the internal facies architecture of the modeled parasequence with the location of flow barriers along the clinoforms shown as black lines. Flow barriers are placed stochastically along clinoforms according to a trend that decreases the probability of barriers being present along the upper part of a clinoform. (C, D) The same depositional-dip-oriented cross section showing water saturation after 5 yr of production where water has been injected down the depositional dip, from east to west, for models with (C) 0% barrier coverage along clinoforms and (D) 90% barrier coverage along clinoforms. Oil is bypassed below the clinoforms in (D). SMB = stream-mouth-bar; pDF = proximal delta-front; dDF = distal delta-front.]]

[[File:BLTN13190fig10.jpg|thumb|400px|{{figure number|10}}(A) Plan-view facies association map of the Ferron Sandstone Member extracted from our reservoir model ([[:File:BLTN13190fig5.jpg|Figure 5D]]), showing location of injector and producer wells, and the cross section illustrated in [[:File:BLTN13190fig10.jpg|Figure 10B–D]]. The color scheme is the same as in [[:File:BLTN13190fig5.jpg|Figures 5D]] and [[:File:BLTN13190fig8.jpg|8A]]. (B) Depositional-dip-oriented cross section showing the internal facies architecture of the modeled parasequence with the location of flow barriers along the clinoforms shown as black lines. Flow barriers are placed stochastically along clinoforms according to a trend that decreases the probability of barriers being present along the upper part of a clinoform. (C, D) The same depositional-dip-oriented cross section showing water saturation after 5 yr of production where water has been injected down the depositional dip, from east to west, for models with (C) 0% barrier coverage along clinoforms and (D) 90% barrier coverage along clinoforms. Oil is bypassed below the clinoforms in (D). SMB = stream-mouth-bar; pDF = proximal delta-front; dDF = distal delta-front.]]

We begin by investigating the ability of the clinoform-modeling algorithm to generate realistic stratal geometries from the Ferron Sandstone Member outcrops. Visual inspection of the algorithm-generated model against outcrop photo pans ([[:File:BLTN13190fig1.jpg|Figure 1]]) and bedding diagram interpretations ([[:File:BLTN13190fig6.jpg|Figure 6A]]) reveals a close correspondence between key geometric aspects of the observed data and concepts reproduced in the model, as outlined below.

We begin by investigating the ability of the clinoform-modeling algorithm to generate realistic stratal geometries from the Ferron Sandstone Member outcrops. Visual inspection of the algorithm-generated model against outcrop photo pans ([[:File:BLTN13190fig1.jpg|Figure 1]]) and bedding diagram interpretations ([[:File:BLTN13190fig6.jpg|Figure 6A]]) reveals a close correspondence between key geometric aspects of the observed data and concepts reproduced in the model, as outlined below.

A single delta lobe is present in the model and extends beyond the model volume ([[:File:BLTN13190fig5.jpg|Figures 5D]], [[:File:BLTN13190fig8.jpg|8A]]). As a result, clinoforms are larger in their depositional dip and strike extent (''t_D'' and ''t_s'', respectively; Table 2) than the model area, and they form arcs in plan view in the model ([[:File:BLTN13190fig8.jpg|Figure 8B]]). This plan-view geometry is consistent with the approximately lobate plan-view geometries of clinoforms in fluvial-dominated deltas ([[:File:BLTN13190fig3.jpg|Figure 3C]]). The clinoform-modeling algorithm generates the concave-upward clinoform geometry observed at the outcrop ([[:File:BLTN13190fig7.jpg|Figures 7B]], [[:File:BLTN13190fig8.jpg|8C]]), while honoring the topography of the parasequence bounding surfaces. The variation in topographic elevation of the modeled parasequence ([[:File:BLTN13190fig7.jpg|Figures 7]], [[:File:BLTN13190fig8.jpg|8]]) is attributed to postdepositional compaction. In a depositional strike cross section of the clinoform-bearing model, the algorithm produces bidirectional concave-upward dips (Figures 7C, 8D) that are consistent with delta-front bodies that are lobate in plan view (e.g., Willis et al.;<ref name=Wllsetal1999 /> Kolla et al.;<ref name=Kll /> Roberts et al.<ref name=Rbrts2004 />). Additionally, the model contains stratal geometries observed at the outcrop, such as onlap and downlap of younger clinoforms on to older clinoforms ([[:File:BLTN13190fig7.jpg|Figures 7B]], [[:File:BLTN13190fig8.jpg|8C]]). The clinoform-modeling algorithm also produces clinoforms that are consistently distributed in the same orientation as those in the observed delta-lobe deposits and its interpreted plan-view progradation direction ([[:File:BLTN13190fig5.jpg|Figures 5A]], [[:File:BLTN13190fig8.jpg|8B]]). Facies proportions in the model are 8% SMB sandstones, 50% pDF sandstones, 31% dDF heteroliths, and 11% PD mudstone. Using porosity values that are characteristic of these facies associations in analogous reservoirs (Table 3), the volume of oil in place in the model is 7.1 million bbl. The clinoform-bearing model is now used to investigate the impact of heterogeneities associated with clinoforms on fluid flow during waterflooding within this fluvial-dominated deltaic parasequence.

A single delta lobe is present in the model and extends beyond the model volume ([[:File:BLTN13190fig5.jpg|Figures 5D]], [[:File:BLTN13190fig8.jpg|8A]]). As a result, clinoforms are larger in their depositional dip and strike extent (''t_D'' and ''t_s'', respectively; Table 2) than the model area, and they form arcs in plan view in the model ([[:File:BLTN13190fig8.jpg|Figure 8B]]). This plan-view geometry is consistent with the approximately lobate plan-view geometries of clinoforms in fluvial-dominated deltas ([[:File:BLTN13190fig3.jpg|Figure 3C]]). The clinoform-modeling algorithm generates the concave-upward clinoform geometry observed at the outcrop ([[:File:BLTN13190fig7.jpg|Figures 7B]], [[:File:BLTN13190fig8.jpg|8C]]), while honoring the topography of the parasequence bounding surfaces. The variation in topographic elevation of the modeled parasequence ([[:File:BLTN13190fig7.jpg|Figures 7]], [[:File:BLTN13190fig8.jpg|8]]) is attributed to postdepositional compaction. In a depositional strike cross section of the clinoform-bearing model, the algorithm produces bidirectional concave-upward dips ([[:File:BLTN13190fig7.jpg|Figures 7C]], [[:File:BLTN13190fig8.jpg|8D]]) that are consistent with delta-front bodies that are lobate in plan view (e.g., Willis et al.;<ref name=Wllsetal1999 /> Kolla et al.;<ref name=Kll /> Roberts et al.<ref name=Rbrts2004 />). Additionally, the model contains stratal geometries observed at the outcrop, such as onlap and downlap of younger clinoforms on to older clinoforms ([[:File:BLTN13190fig7.jpg|Figures 7B]], [[:File:BLTN13190fig8.jpg|8C]]). The clinoform-modeling algorithm also produces clinoforms that are consistently distributed in the same orientation as those in the observed delta-lobe deposits and its interpreted plan-view progradation direction ([[:File:BLTN13190fig5.jpg|Figures 5A]], [[:File:BLTN13190fig8.jpg|8B]]). Facies proportions in the model are 8% SMB sandstones, 50% pDF sandstones, 31% dDF heteroliths, and 11% PD mudstone. Using porosity values that are characteristic of these facies associations in analogous reservoirs (Table 3), the volume of oil in place in the model is 7.1 million bbl. The clinoform-bearing model is now used to investigate the impact of heterogeneities associated with clinoforms on fluid flow during waterflooding within this fluvial-dominated deltaic parasequence.

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The clinoforms incorporated into the Troll sector model show similar geometries and spacing to those that are seismically resolved in the Sognefjord Formation.<ref name=Dryr2005 /><ref name=Ptrno /> The clinoforms are linear in plan view over the small (750 m [2461 ft]) depositional-strike extent of the model ([[:File:BLTN13190fig14.jpg|Figure 14B]]), consistent with the interpreted plan-view geometries of wave-dominated shoreface systems ([[:File:BLTN13190fig3.jpg|Figure 3A]]),<ref name=Hwll2008a /> consistently prograde west-northwestward (θ = 320°), as established through 3-D seismic data,<ref name=Dryr2005 /><ref name=Ptrno /> and have the concave-upward geometry observed in seismic dip sections through the Sognefjord Formation<ref name=Dryr2005 /><ref name=Ptrno /> (Figures 14A, 15B). In depositional strike cross section, the algorithm produces near-horizontal clinoform geometries, consistent with seismically resolved clinoforms<ref name=Dryr2005 /><ref name=Ptrno /> ([[:File:BLTN13190fig15.jpg|Figure 15C]]). The stochastic component of the clinoform-modeling algorithm distributes clinoforms with cross-sectional geometries and spacings (Figures 14A, 15B) that are consistent with outcrop studies of wave-dominated deltas<ref name=Hmpsn2000>Hampson, G. J., 2000, Discontinuity surfaces, clinoforms and facies architecture in a wave-dominated, shoreface-shelf parasequence: Journal of Sedimentary Research, v. 70, no. 2, p. 325–340, doi: 10.1306/2DC40914-0E47-11D7-8643000102C1865D.</ref><ref name=Sch09 /> ([[:File:BLTN13190fig13.jpg|Figure 13]]) and honor the sparse subsurface data. In contrast to the Ferron Sandstone Member example, the Troll West sector model does not contain subtle clinoform geometries, such as onlap and downlap of younger clinoforms on to older clinoforms ([[:File:BLTN13190fig14.jpg|Figures 14A]], [[:File:BLTN13190fig15.jpg|15B]]). Such features are below the resolution of the seismic data used to extract the parameters that were used in the algorithm. The clinoforms are also faulted in the same way as the parasequence-bounding flooding surfaces (cf. [[:File:BLTN13190fig2.jpg|Figures 2A]], [[:File:BLTN13190fig15.jpg|15C]]).

The clinoforms incorporated into the Troll sector model show similar geometries and spacing to those that are seismically resolved in the Sognefjord Formation.<ref name=Dryr2005 /><ref name=Ptrno /> The clinoforms are linear in plan view over the small (750 m [2461 ft]) depositional-strike extent of the model ([[:File:BLTN13190fig14.jpg|Figure 14B]]), consistent with the interpreted plan-view geometries of wave-dominated shoreface systems ([[:File:BLTN13190fig3.jpg|Figure 3A]]),<ref name=Hwll2008a /> consistently prograde west-northwestward (θ = 320°), as established through 3-D seismic data,<ref name=Dryr2005 /><ref name=Ptrno /> and have the concave-upward geometry observed in seismic dip sections through the Sognefjord Formation<ref name=Dryr2005 /><ref name=Ptrno /> ([[:File:BLTN13190fig14.jpg|Figures 14A]], [[:File:BLTN13190fig15.jpg|15B]]). In depositional strike cross section, the algorithm produces near-horizontal clinoform geometries, consistent with seismically resolved clinoforms<ref name=Dryr2005 /><ref name=Ptrno /> ([[:File:BLTN13190fig15.jpg|Figure 15C]]). The stochastic component of the clinoform-modeling algorithm distributes clinoforms with cross-sectional geometries and spacings ([[:File:BLTN13190fig14.jpg|Figures 14A]], [[:File:BLTN13190fig15.jpg|15B]]) that are consistent with outcrop studies of wave-dominated deltas<ref name=Hmpsn2000>Hampson, G. J., 2000, Discontinuity surfaces, clinoforms and facies architecture in a wave-dominated, shoreface-shelf parasequence: Journal of Sedimentary Research, v. 70, no. 2, p. 325–340, doi: 10.1306/2DC40914-0E47-11D7-8643000102C1865D.</ref><ref name=Sch09 /> ([[:File:BLTN13190fig13.jpg|Figure 13]]) and honor the sparse subsurface data. In contrast to the Ferron Sandstone Member example, the Troll West sector model does not contain subtle clinoform geometries, such as onlap and downlap of younger clinoforms on to older clinoforms ([[:File:BLTN13190fig14.jpg|Figures 14A]], [[:File:BLTN13190fig15.jpg|15B]]). Such features are below the resolution of the seismic data used to extract the parameters that were used in the algorithm. The clinoforms are also faulted in the same way as the parasequence-bounding flooding surfaces (cf. [[:File:BLTN13190fig2.jpg|Figures 2A]], [[:File:BLTN13190fig15.jpg|15C]]).

===Production Strategy===

===Production Strategy===

[[File:BLTN13190fig16.jpg|thumb|400px|{{figure number|16}}(A) Plan-view facies-association map through the uppermost parasequence of the Sognefjord Formation in our Troll West sector model, showing the location of the horizontal well and the cross section shown in [[:File:BLTN13190fig16.jpg|Figure 16B–D]]. (B) Depositional-dip-oriented cross section showing the internal facies architecture of the modeled parasequences with the location of barriers along the clinoforms shown as black lines. (C, D) The same depositional-dip-oriented cross section showing water saturation after 1000 days of production, for models with (C) 0% barrier coverage along clinoforms and (D) 90% barrier coverage along clinoforms.]]

[[File:BLTN13190fig16.jpg|thumb|400px|{{figure number|16}}(A) Plan-view facies-association map through the uppermost parasequence of the Sognefjord Formation in our Troll West sector model, showing the location of the horizontal well and the cross section shown in [[:File:BLTN13190fig16.jpg|Figure 16B–D]]. (B) Depositional-dip-oriented cross section showing the internal facies architecture of the modeled parasequences with the location of barriers along the clinoforms shown as black lines. (C, D) The same depositional-dip-oriented cross section showing water saturation after 1000 days of production, for models with (C) 0% barrier coverage along clinoforms and (D) 90% barrier coverage along clinoforms.]]

The clinoform-bearing Troll West sector model was then used to simulate production through gas expansion and aquifer influx using a 2600 m (8530 ft) long horizontal well, placed 2 m (7 ft) above the initial OWC (Figures 15A, 16A). The well is controlled by maximum gas production rate, minimum oil production rate, and minimum bottom-hole-pressure constraints. Reservoir, rock, and fluid properties are summarized in Table 5. Similar to the Ferron Sandstone Member example, the presence of permeability barriers along clinoforms was modeled using transmissibility modifiers and specified in terms of the percentage of each clinoform surface that acts as a barrier to flow. Two simulations of the Troll Field sector model were conducted in which (1) clinoforms are not associated with barriers to flow (0% barrier coverage along clinoforms) and (2) clinoforms are associated with significant barriers to flow (90% barrier coverage along clinoforms, [[:File:BLTN13190fig16.jpg|Figure 16B]]). All other parameters remain fixed between the simulations.

The clinoform-bearing Troll West sector model was then used to simulate production through gas expansion and aquifer influx using a 2600 m (8530 ft) long horizontal well, placed 2 m (7 ft) above the initial OWC ([[:File:BLTN13190fig15.jpg|Figures 15A]], [[:File:BLTN13190fig16.jpg|16A]]). The well is controlled by maximum gas production rate, minimum oil production rate, and minimum bottom-hole-pressure constraints. Reservoir, rock, and fluid properties are summarized in Table 5. Similar to the Ferron Sandstone Member example, the presence of permeability barriers along clinoforms was modeled using transmissibility modifiers and specified in terms of the percentage of each clinoform surface that acts as a barrier to flow. Two simulations of the Troll Field sector model were conducted in which (1) clinoforms are not associated with barriers to flow (0% barrier coverage along clinoforms) and (2) clinoforms are associated with significant barriers to flow (90% barrier coverage along clinoforms, [[:File:BLTN13190fig16.jpg|Figure 16B]]). All other parameters remain fixed between the simulations.

===Simulation Results===

===Simulation Results===