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Clinoform surfaces control aspects of facies architecture within shallow-marine parasequences and can also act as barriers or baffles to flow where they are lined by low-permeability lithologies, such as cements or mudstones. Current reservoir modeling techniques are not well suited to capturing clinoforms, particularly if they are numerous, below seismic resolution, and/or difficult to correlate between wells. At present, there are no modeling tools available to automate the generation of multiple three-dimensional clinoform surfaces using a small number of input parameters. Consequently, clinoforms are rarely incorporated in models of shallow-marine reservoirs, even when their potential impact on fluid flow is recognized.

Clinoform surfaces control aspects of facies architecture within shallow-marine parasequences and can also act as barriers or baffles to flow where they are lined by low-permeability lithologies, such as cements or [[mudstones]]. Current reservoir modeling techniques are not well suited to capturing clinoforms, particularly if they are numerous, below seismic resolution, and/or difficult to correlate between wells. At present, there are no modeling tools available to automate the generation of multiple three-dimensional clinoform surfaces using a small number of input parameters. Consequently, clinoforms are rarely incorporated in models of shallow-marine reservoirs, even when their potential impact on fluid flow is recognized.

A numerical algorithm that generates multiple clinoforms within a volume defined by two bounding surfaces, such as a delta-lobe deposit or shoreface parasequence, is developed. A geometric approach is taken to construct the shape of a clinoform, combining its height relative to the bounding surfaces with a mathematical function that describes clinoform geometry. The method is flexible, allowing the user to define the progradation direction and the parameters that control the geometry and distribution of individual clinoforms. The algorithm is validated via construction of surface-based three-dimensional reservoir models of (1) fluvial-dominated delta-lobe deposits exposed at the outcrop (Cretaceous Ferron Sandstone Member, Utah), and (2) a sparse subsurface data set from a deltaic reservoir (Jurassic Sognefjord Formation, Troll Field, Norwegian North Sea). Resulting flow simulation results demonstrate the value of including algorithm-generated clinoforms in reservoir models, because they may significantly impact hydrocarbon recovery when associated with areally extensive barriers to flow.

A numerical algorithm that generates multiple clinoforms within a volume defined by two bounding surfaces, such as a delta-lobe deposit or shoreface parasequence, is developed. A geometric approach is taken to construct the shape of a clinoform, combining its height relative to the bounding surfaces with a mathematical function that describes clinoform geometry. The method is flexible, allowing the user to define the progradation direction and the parameters that control the geometry and distribution of individual clinoforms. The algorithm is validated via construction of surface-based three-dimensional reservoir models of (1) fluvial-dominated delta-lobe deposits exposed at the outcrop (Cretaceous Ferron Sandstone Member, Utah), and (2) a sparse subsurface data set from a deltaic reservoir (Jurassic Sognefjord Formation, Troll Field, Norwegian North Sea). Resulting flow simulation results demonstrate the value of including algorithm-generated clinoforms in reservoir models, because they may significantly impact hydrocarbon recovery when associated with areally extensive barriers to flow.

===Cross-Sectional Clinoform Geometry===

===Cross-Sectional Clinoform Geometry===

The shape and dip angle of a deltaic or shoreface clinoform in [[cross section]] is a function of modal grain size, proportion of mud, and the depositional process regime at the shoreline. In sandy, fluvial-dominated deltas, clinoforms have simple concave-upward geometries and steep dip angles (up to 15°)<ref name=GB05 /> (e.g., [[:File:BLTN13190fig1.jpg|Figure 1]]). Similar geometries have been documented in sandy, tide-influenced deltas (dip angles up to 5°–15°).<ref name=Wllsetal1999>Willis, B. J., J. P. Bhattacharya, S. L. Gabel, and C. D. White, 1999, Architecture of a tide-influenced river delta in the Frontier Formation of central Wyoming, USA: Sedimentology, v. 46, no. 4, p. 667–688, doi: 10.1046/j.1365-3091.1999.00239.x.</ref> Concave-upward clinoform geometry is also typical of sandy, wave-dominated deltas and strandplains, although the clinoforms have smaller dip angles (typically up to 1°–2°).<ref>Hampson, G. J., and J. E. A. Storms, 2003, Geomorphological and sequence stratigraphic variability in wave-dominated shoreface-shelf parasequences: Sedimentology, v. 50, no. 4, p. 667–701, doi: 10.1046/j.1365-3091.2003.00570.x.</ref><ref name=GB05 /> Clinoforms are consistently inclined paleobasinward down depositional dip; and, along depositional strike, they exhibit bidirectional, concave-upward dips if the delta-front was lobate in plan view (e.g., Willis et al.;<ref name=Wllsetal1999 /> Kolla et al.;<ref name=Kll>Kolla, V., P. Biondi, B. Long, and R. Fillon, 2000, Sequence stratigraphy and architecture of the late Pleistocene Lagniappe delta complex, northeast Gulf of Mexico, inD. Hunt, and R. L. Gawthorpe, eds., Sedimentary responses to forced regressions: Geological Society, London, Special Publication 172, p. 291–327.</ref> Roberts et al.<ref name=Rbrts2004 />) or appear horizontal if the shoreline was approximately linear (e.g., Hampson<ref name=Hmpsn2000 />). Clinoforms are usually truncated at their tops by a variety of channelized erosion surfaces formed during shoreline advance (e.g., distributary channels, incised valleys) and by channelized and/or planar transgressive erosion surfaces (tide and wave ravinement surfaces sense Swift<ref>Swift, D. J., 1968, Coastal erosion and transgressive stratigraphy: Journal of Geology, v. 76, no. 4, p. 444–456, doi: 10.1086/jg.1968.76.issue-4.</ref>) associated with shoreline retreat. Consequently, most sandy shoreline clinoforms lack a decrease in depositional dip (rollover) near their tops, although this geometry is ubiquitous in larger, shelf-slope margin clinoforms (e.g., Steckler et al.<ref name=Stcklr1999>Steckler, M. S., G. S. Mountain, K. G. Miller, and N. Christie-Blick, 1999, Reconstruction of tertiary progradation and clinoform development on the New Jersey passive margin by 2D backstripping: Marine Geology, v. 154, no. 1–4, p. 399–420, doi: 10.1016/S0025-3227(98)00126-1.</ref>) and in the outer, muddy portion of compound deltaic clinoforms with a broad subaqueous topset that lies seaward of the shoreline (e.g., Pirmez et al.<ref>Pirmez, C., L. F. Pratson, and M. S. Steckler, 1998, Clinoform development by advection-diffusion of suspended sediment; modeling and comparison to natural systems: Journal of Geophysical Research B: Solid Earth and Planets, v. 103, p. 24,141–24,157, doi: 10.1029/98JB01516.</ref>).

The shape and dip angle of a deltaic or shoreface clinoform in [[cross section]] is a function of modal [[grain size]], proportion of mud, and the depositional process regime at the shoreline. In sandy, fluvial-dominated deltas, clinoforms have simple concave-upward geometries and steep dip angles (up to 15°)<ref name=GB05 /> (e.g., [[:File:BLTN13190fig1.jpg|Figure 1]]). Similar geometries have been documented in sandy, tide-influenced deltas (dip angles up to 5°–15°).<ref name=Wllsetal1999>Willis, B. J., J. P. Bhattacharya, S. L. Gabel, and C. D. White, 1999, Architecture of a tide-influenced river delta in the Frontier Formation of central Wyoming, USA: Sedimentology, v. 46, no. 4, p. 667–688, doi: 10.1046/j.1365-3091.1999.00239.x.</ref> Concave-upward clinoform geometry is also typical of sandy, wave-dominated deltas and strandplains, although the clinoforms have smaller dip angles (typically up to 1°–2°).<ref>Hampson, G. J., and J. E. A. Storms, 2003, Geomorphological and sequence stratigraphic variability in wave-dominated shoreface-shelf parasequences: Sedimentology, v. 50, no. 4, p. 667–701, doi: 10.1046/j.1365-3091.2003.00570.x.</ref><ref name=GB05 /> Clinoforms are consistently inclined paleobasinward down depositional dip; and, along depositional strike, they exhibit bidirectional, concave-upward dips if the delta-front was lobate in plan view (e.g., Willis et al.;<ref name=Wllsetal1999 /> Kolla et al.;<ref name=Kll>Kolla, V., P. Biondi, B. Long, and R. Fillon, 2000, Sequence stratigraphy and architecture of the late Pleistocene Lagniappe delta complex, northeast Gulf of Mexico, inD. Hunt, and R. L. Gawthorpe, eds., Sedimentary responses to forced regressions: Geological Society, London, Special Publication 172, p. 291–327.</ref> Roberts et al.<ref name=Rbrts2004 />) or appear horizontal if the shoreline was approximately linear (e.g., Hampson<ref name=Hmpsn2000 />). Clinoforms are usually truncated at their tops by a variety of channelized erosion surfaces formed during shoreline advance (e.g., distributary channels, incised valleys) and by channelized and/or planar transgressive erosion surfaces (tide and wave ravinement surfaces sense Swift<ref>Swift, D. J., 1968, Coastal erosion and transgressive stratigraphy: Journal of Geology, v. 76, no. 4, p. 444–456, doi: 10.1086/jg.1968.76.issue-4.</ref>) associated with shoreline retreat. Consequently, most sandy shoreline clinoforms lack a decrease in depositional dip (rollover) near their tops, although this geometry is ubiquitous in larger, shelf-slope margin clinoforms (e.g., Steckler et al.<ref name=Stcklr1999>Steckler, M. S., G. S. Mountain, K. G. Miller, and N. Christie-Blick, 1999, Reconstruction of tertiary progradation and clinoform development on the New Jersey passive margin by 2D backstripping: Marine Geology, v. 154, no. 1–4, p. 399–420, doi: 10.1016/S0025-3227(98)00126-1.</ref>) and in the outer, muddy portion of compound deltaic clinoforms with a broad subaqueous topset that lies seaward of the shoreline (e.g., Pirmez et al.<ref>Pirmez, C., L. F. Pratson, and M. S. Steckler, 1998, Clinoform development by advection-diffusion of suspended sediment; modeling and comparison to natural systems: Journal of Geophysical Research B: Solid Earth and Planets, v. 103, p. 24,141–24,157, doi: 10.1029/98JB01516.</ref>).

Here, a geometric approach is used to represent the depositional dip cross-section shape of a clinoform with a dimensionless shape function, ''s(r_c)'' ([[:File:BLTN13190fig2.jpg|Figure 2E]]), such as a power law for concave-upward, sandy, shoreline clinoforms:  

Here, a geometric approach is used to represent the depositional dip cross-section shape of a clinoform with a dimensionless shape function, ''s(r_c)'' ([[:File:BLTN13190fig2.jpg|Figure 2E]]), such as a power law for concave-upward, sandy, shoreline clinoforms:  

===Geological Setting===

===Geological Setting===

Construction and fluid-flow simulation of models based on outcrop analogs is an established method for investigating geologic controls on subsurface reservoir performance (e.g., Ciammetti et al.;<ref>Ciammetti, G., P. S. Ringrose, T. R. Good, J. M. L. Lewis, and K. S. Sorbie, 1995, Waterflood recovery and fluid flow upscaling in a shallow marine and fluvial sandstone sequence: SPE Paper 30783, 14 p.</ref> White and Barton;<ref name=WB1999>White, C. D., and M. D. Barton, 1999, Translating outcrop data to flow models, with applications to the Ferron Sandstone: SPE Reservoir Evaluation and Engineering, v. 2, no. 4, p. 341–350, doi: 10.2118/57482-PA.</ref> White et al.;<ref>White, C. D., B. J. Willis, S. P. Dutton, J. P. Bhattacharya, and K. Narayanan, 2004, [http://archives.datapages.com/data/specpubs/memoir80/CHAPTER7/CHAPTER7.HTM Sedimentology, statistics, and flow behaviour for a tide-influenced deltaic sandstone, Frontier Formation, Wyoming, United States], in G. M. Grammer, P. M. Harris, and G. P. Eberli, eds., Integration of outcrop and modern analogs in reservoir modeling: [http://store.aapg.org/detail.aspx?id=658 AAPG Memoir 80], p. 129–152.</ref> Jackson et al.;<ref name=Jckson2009 /> Sech et al.;<ref name=Sch09 /> Enge and Howell<ref name=EH2010 />). Here, the clinoform-modeling algorithm is used to build a reservoir model utilizing a high-resolution outcrop data set from the Ferron Sandstone Member, Utah, at a scale that is comparable to the interwell spacing (750 × 3000 m [2461 × 9843 ft] areally) in a typical hydrocarbon reservoir and captures several tens of clinoforms and their associated heterogeneities. Previously, Forster et al. <ref name=Frstr2004 /> constructed 2-D flow-simulation models of the same outcrop analog via data-intensive, deterministic mapping of clinoforms and facies boundaries in cliff-face exposures. In contrast, our aim is to verify that the clinoform-modeling algorithm can produce realistic 3-D stratigraphic architectures that mimic rich outcrop data sets when conditioned to sparse input data that are typical in the subsurface. The scale of the model fills the gap between detailed but sparse 2-D core and well-log data and low-resolution but extensive 3-D seismic data.

Construction and fluid-flow simulation of models based on outcrop analogs is an established method for investigating geologic controls on subsurface reservoir performance (e.g., Ciammetti et al.;<ref>Ciammetti, G., P. S. Ringrose, T. R. Good, J. M. L. Lewis, and K. S. Sorbie, 1995, Waterflood recovery and fluid flow upscaling in a shallow marine and fluvial sandstone sequence: SPE Paper 30783, 14 p.</ref> White and Barton;<ref name=WB1999>White, C. D., and M. D. Barton, 1999, Translating outcrop data to flow models, with applications to the Ferron Sandstone: SPE Reservoir Evaluation and Engineering, v. 2, no. 4, p. 341–350, doi: 10.2118/57482-PA.</ref> White et al.;<ref>White, C. D., B. J. Willis, S. P. Dutton, J. P. Bhattacharya, and K. Narayanan, 2004, [http://archives.datapages.com/data/specpubs/memoir80/CHAPTER7/CHAPTER7.HTM Sedimentology, statistics, and flow behaviour for a tide-influenced deltaic sandstone, Frontier Formation, Wyoming, United States], in G. M. Grammer, P. M. Harris, and G. P. Eberli, eds., Integration of outcrop and modern analogs in reservoir modeling: [http://store.aapg.org/detail.aspx?id=658 AAPG Memoir 80], p. 129–152.</ref> Jackson et al.;<ref name=Jckson2009 /> Sech et al.;<ref name=Sch09 /> Enge and Howell<ref name=EH2010 />). Here, the clinoform-modeling algorithm is used to build a reservoir model utilizing a high-resolution outcrop data set from the Ferron Sandstone Member, Utah, at a scale that is comparable to the interwell spacing (750 × 3000 m [2461 × 9843 ft] areally) in a typical [[hydrocarbon reservoir]] and captures several tens of clinoforms and their associated heterogeneities. Previously, Forster et al. <ref name=Frstr2004 /> constructed 2-D flow-simulation models of the same outcrop analog via data-intensive, deterministic mapping of clinoforms and facies boundaries in cliff-face exposures. In contrast, our aim is to verify that the clinoform-modeling algorithm can produce realistic 3-D stratigraphic architectures that mimic rich outcrop data sets when conditioned to sparse input data that are typical in the subsurface. The scale of the model fills the gap between detailed but sparse 2-D core and well-log data and low-resolution but extensive 3-D seismic data.

The Ferron Sandstone Member of the Mancos Shale is located in east-central Utah. The unit was deposited during the Late Cretaceous (Turonian–Coniacian) on the western margin of the Western Interior Seaway and, in the study area, records the progradation of the Last Chance delta system from southwest (paleolandward) to northeast (paleoseaward)<ref name=cttr /> ([[:File:BLTN13190fig5.jpg|Figure 5A]]). These deltaic deposits form a basinward-thinning wedge that passes eastward into the offshore deposits of the Mancos Shale. The wedge contains either seven<ref>Ryer, T. A., 1991, Stratigraphy, facies and depositional history of the Ferron Sandstone in the Canyon of Muddy Creek, east-central Utah, inT. C. Chidsey, Jr., ed., Geology of east-central Utah: Utah Geological Association Publication 19, p. 45–54.</ref><ref name=Grdnr>Gardner, M. H., 1993, Sequence stratigraphy and facies architecture of the Upper Cretaceous Ferron Sandstone Member of the Mancos Shale, east-central Utah: Ph.D. dissertation, Colorado School of Mines, Golden, Colorado, 528 p.</ref><ref>Barton, M. D., E. S. Angle, and N. Tyler, 2004, [http://archives.datapages.com/data/specpubs/study50/sg50ch07/sg50ch07.htm Stratigraphic architecture of fluvial-deltaic sandstones from the Ferron Sandstone outcrop, east-central Utah], in T. C. Chidsey, Jr., R. D. Adams, and T. H. Morris, eds., Regional to wellbore analog for fluvial-deltaic reservoir modeling: The Ferron Sandstone of Utah: [http://store.aapg.org/detail.aspx?id=655 AAPG Studies in Geology 50], p. 193–210.</ref> or eight sandstone tongues,<ref name=AndrsnRyr2004 /><ref name=GvdB2004 /> such that one tongue is equivalent to a parasequence set of Deveugle et al.<ref name=Dvgl2011 /> ([[:File:BLTN13190fig5.jpg|Figure 5B]]). A single delta-lobe deposit within the lowermost sandstone tongue is the focus of the study (bedset Kf-1-Iv[a] of Anderson et al.;<ref name=Andrsn2004>Anderson, P. B., T. C. Chidsey, Jr., T. A. Ryer, R. D. Adams, and K. McClure, 2004, [http://archives.datapages.com/data/specpubs/study50/sg50ch13/sg50ch13.htm Geological framework, facies paleogeography, and reservoir analogs of the Ferron Sandstone in the Ivie Creek area, east-central Utah], in T. C. Chidsey, Jr., R. D. Adams, and T. H. Morris, eds., Regional to wellbore analog for fluvial-deltaic reservoir modeling: The Ferron Sandstone of Utah: [http://store.aapg.org/detail.aspx?id=655 AAPG Studies in Geology 50], p. 331–356.</ref> parasequence 1h of Garrison and Van den Bergh;<ref name=GvdB2004 /> parasequence 1.6 of Deveugle et al.<ref name=Dvgl2011 />) ([[:File:BLTN13190fig5.jpg|Figure 5C, D]]). The delta-lobe deposit is fluvial dominated with low-to-moderate wave influence<ref name=Grdnr /><ref name=GvdB2004 /><ref>Ryer, T. A., and P. B. Anderson, 2004, [http://archives.datapages.com/data/specpubs/study50/sg50ch03/sg50ch03.htm Facies of the Ferron Sandstone, east-central Utah], in T. C. Chidsey, Jr., R. D. Adams, and T. H. Morris, eds., Regional to wellbore analog for fluvial-deltaic reservoir modeling: The Ferron Sandstone of Utah: [http://store.aapg.org/detail.aspx?id=655 AAPG Studies in Geology 50], p. 59–78.</ref> and contains numerous, well-documented clinoforms in the exposures of the Ivie Creek amphitheater<ref>Anderson, P. B., T. C. Chidsey, Jr., K. McClure, A. Mattson, and S. H. Snelgrove, 2002, Ferron Sandstone stratigraphic cross-sections, Ivie Creek area, Emery County, Utah: Utah Geological Survey, Open File Report 390, CD-ROM.</ref><ref>Anderson, P. B., K. McClure, T. C. Chidsey, Jr., T. A. Ryer, T. H. Morris, J. A. Dewey, Jr., and R. D. Adams, 2003, Interpreted regional photomosaics and cross sections, Cretaceous Ferron Sandstone, east-central Utah: Utah Geological Survey, Open File Report 412, CD-ROM.</ref><ref name=Andrsn2004 /><ref name=Frstr2004 /><ref name=EH2010 /> ([[:File:BLTN13190fig5.jpg|Figure 5D]]). Clinoform-related bedding geometries and facies distributions imply that clinoforms mapped by previous workers, and used as input data for the models presented below ([[:File:BLTN13190fig6.jpg|Figure 6A]], after Forster et al. <ref name=Frstr2004 />), bound clinothems equivalent to mouth bars (sensu Bhattacharya<ref name=Bhttchry2006 />). Subtle, apparently cyclic variations in clinoform spacing and dip angle probably define mouth-bar assemblages (sensu Bhattacharya;<ref name=Bhttchry2006 /> “bedsets” sensu Enge et al.<ref name=Eng2010>Enge, H. D., J. A. Howell, and S. Buckley, 2010, The geometry and internal architecture of stream mouth bars in the Panther Tongue and the Ferron Sandstone Members, Utah, U.S.A.: Journal of Sedimentary Research, v. 80, no. 11, p. 1018–1031, doi: 10.2110/jsr.2010.088.</ref>). Smaller-scale lithologic variation at the scale of individual beds occurs between the mapped clinoforms and records incremental growth of a mouth bar because of varying water and sediment discharge through the feeder distributary channel. Deveugle et al.<ref name=Dvgl2011 /> used a high-resolution outcrop data set to build a reservoir-scale (7200 × 3800 × 50 m [23622 × 12467 × 164 ft]), surface-based model of the lower two tongues (parasequence sets) of the Ferron Sandstone Member. Clinoforms were not represented in the delta-lobe deposits (cf. parasequences) of the Deveugle et al.<ref name=Dvgl2011 /> model, and their surface-based model is used here as the context in which the clinoform-modeling algorithm should be applied.

The Ferron Sandstone Member of the Mancos Shale is located in east-central Utah. The unit was deposited during the Late Cretaceous (Turonian–Coniacian) on the western margin of the Western Interior Seaway and, in the study area, records the progradation of the Last Chance delta system from southwest (paleolandward) to northeast (paleoseaward)<ref name=cttr /> ([[:File:BLTN13190fig5.jpg|Figure 5A]]). These deltaic deposits form a basinward-thinning wedge that passes eastward into the offshore deposits of the Mancos Shale. The wedge contains either seven<ref>Ryer, T. A., 1991, Stratigraphy, facies and depositional history of the Ferron Sandstone in the Canyon of Muddy Creek, east-central Utah, inT. C. Chidsey, Jr., ed., Geology of east-central Utah: Utah Geological Association Publication 19, p. 45–54.</ref><ref name=Grdnr>Gardner, M. H., 1993, Sequence stratigraphy and facies architecture of the Upper Cretaceous Ferron Sandstone Member of the Mancos Shale, east-central Utah: Ph.D. dissertation, Colorado School of Mines, Golden, Colorado, 528 p.</ref><ref>Barton, M. D., E. S. Angle, and N. Tyler, 2004, [http://archives.datapages.com/data/specpubs/study50/sg50ch07/sg50ch07.htm Stratigraphic architecture of fluvial-deltaic sandstones from the Ferron Sandstone outcrop, east-central Utah], in T. C. Chidsey, Jr., R. D. Adams, and T. H. Morris, eds., Regional to wellbore analog for fluvial-deltaic reservoir modeling: The Ferron Sandstone of Utah: [http://store.aapg.org/detail.aspx?id=655 AAPG Studies in Geology 50], p. 193–210.</ref> or eight sandstone tongues,<ref name=AndrsnRyr2004 /><ref name=GvdB2004 /> such that one tongue is equivalent to a parasequence set of Deveugle et al.<ref name=Dvgl2011 /> ([[:File:BLTN13190fig5.jpg|Figure 5B]]). A single delta-lobe deposit within the lowermost sandstone tongue is the focus of the study (bedset Kf-1-Iv[a] of Anderson et al.;<ref name=Andrsn2004>Anderson, P. B., T. C. Chidsey, Jr., T. A. Ryer, R. D. Adams, and K. McClure, 2004, [http://archives.datapages.com/data/specpubs/study50/sg50ch13/sg50ch13.htm Geological framework, facies paleogeography, and reservoir analogs of the Ferron Sandstone in the Ivie Creek area, east-central Utah], in T. C. Chidsey, Jr., R. D. Adams, and T. H. Morris, eds., Regional to wellbore analog for fluvial-deltaic reservoir modeling: The Ferron Sandstone of Utah: [http://store.aapg.org/detail.aspx?id=655 AAPG Studies in Geology 50], p. 331–356.</ref> parasequence 1h of Garrison and Van den Bergh;<ref name=GvdB2004 /> parasequence 1.6 of Deveugle et al.<ref name=Dvgl2011 />) ([[:File:BLTN13190fig5.jpg|Figure 5C, D]]). The delta-lobe deposit is fluvial dominated with low-to-moderate wave influence<ref name=Grdnr /><ref name=GvdB2004 /><ref>Ryer, T. A., and P. B. Anderson, 2004, [http://archives.datapages.com/data/specpubs/study50/sg50ch03/sg50ch03.htm Facies of the Ferron Sandstone, east-central Utah], in T. C. Chidsey, Jr., R. D. Adams, and T. H. Morris, eds., Regional to wellbore analog for fluvial-deltaic reservoir modeling: The Ferron Sandstone of Utah: [http://store.aapg.org/detail.aspx?id=655 AAPG Studies in Geology 50], p. 59–78.</ref> and contains numerous, well-documented clinoforms in the exposures of the Ivie Creek amphitheater<ref>Anderson, P. B., T. C. Chidsey, Jr., K. McClure, A. Mattson, and S. H. Snelgrove, 2002, Ferron Sandstone stratigraphic cross-sections, Ivie Creek area, Emery County, Utah: Utah Geological Survey, Open File Report 390, CD-ROM.</ref><ref>Anderson, P. B., K. McClure, T. C. Chidsey, Jr., T. A. Ryer, T. H. Morris, J. A. Dewey, Jr., and R. D. Adams, 2003, Interpreted regional photomosaics and cross sections, Cretaceous Ferron Sandstone, east-central Utah: Utah Geological Survey, Open File Report 412, CD-ROM.</ref><ref name=Andrsn2004 /><ref name=Frstr2004 /><ref name=EH2010 /> ([[:File:BLTN13190fig5.jpg|Figure 5D]]). Clinoform-related bedding geometries and facies distributions imply that clinoforms mapped by previous workers, and used as input data for the models presented below ([[:File:BLTN13190fig6.jpg|Figure 6A]], after Forster et al. <ref name=Frstr2004 />), bound clinothems equivalent to mouth bars (sensu Bhattacharya<ref name=Bhttchry2006 />). Subtle, apparently cyclic variations in clinoform spacing and dip angle probably define mouth-bar assemblages (sensu Bhattacharya;<ref name=Bhttchry2006 /> “bedsets” sensu Enge et al.<ref name=Eng2010>Enge, H. D., J. A. Howell, and S. Buckley, 2010, The geometry and internal architecture of stream mouth bars in the Panther Tongue and the Ferron Sandstone Members, Utah, U.S.A.: Journal of Sedimentary Research, v. 80, no. 11, p. 1018–1031, doi: 10.2110/jsr.2010.088.</ref>). Smaller-scale lithologic variation at the scale of individual beds occurs between the mapped clinoforms and records incremental growth of a mouth bar because of varying water and sediment discharge through the feeder distributary channel. Deveugle et al.<ref name=Dvgl2011 /> used a high-resolution outcrop data set to build a reservoir-scale (7200 × 3800 × 50 m [23622 × 12467 × 164 ft]), surface-based model of the lower two tongues (parasequence sets) of the Ferron Sandstone Member. Clinoforms were not represented in the delta-lobe deposits (cf. parasequences) of the Deveugle et al.<ref name=Dvgl2011 /> model, and their surface-based model is used here as the context in which the clinoform-modeling algorithm should be applied.

</gallery>

</gallery>

The top and base flooding surfaces of parasequence 1.6 were extracted from the model of Deveugle et al.<ref name=Dvgl2011 /> and served as the bounding surfaces used in the clinoform algorithm ([[:File:BLTN13190fig2.jpg|Figure 2]]). The surfaces were cropped to cover a model area of 750 × 3000 m (2461 × 9843 ft) in the Ivie Creek amphitheater ([[:File:BLTN13190fig5.jpg|Figure 5D]]). Additional surfaces representing the boundaries between facies associations from the model of Deveugle et al.<ref name=Dvgl2011 /> were also extracted and similarly cropped; these define the distribution of facies associations present in each rock volume bounded by two clinoforms (i.e., clinothem) (cf. table 1 in Deveugle et al.<ref name=Dvgl2011 />). From distal to proximal, the modeled facies associations are prodelta mudstone (PD), distal delta-front heteroliths (dDF), proximal delta-front sandstones (pDF), and stream-mouth-bar sandstones (SMB) ([[:File:BLTN13190fig5.jpg|Figure 5D]]). Where facies associations pinch out, the facies association boundary surfaces were adjusted to coincide throughout the remainder of the model volume with either the top or base parasequence bounding surface. This ensures that the surface is defined across the entire model volume and is suitable for gridding.<ref name=Jckson2009 /> There are no faults within the model volume of 750 × 3000 × 6 m (2461 × 9843 × 20 ft). In a final step, isochore maps were generated between the top and base flooding surfaces and between facies association boundary surfaces and the base flooding surface. The base bounding surface was flattened, to mimic clinoform progradation over a flat, horizontal sea floor, and isochore maps were used to modify the geometries of the top bounding surface and facies association boundary surfaces above this horizontal base surface. As a result of flattening on the base bounding surface, the bounding surfaces from the existing model of Deveugle et al.<ref name=Dvgl2011 /> have been modified.

The top and base flooding surfaces of parasequence 1.6 were extracted from the model of Deveugle et al.<ref name=Dvgl2011 /> and served as the bounding surfaces used in the clinoform algorithm ([[:File:BLTN13190fig2.jpg|Figure 2]]). The surfaces were cropped to cover a model area of 750 × 3000 m (2461 × 9843 ft) in the Ivie Creek amphitheater ([[:File:BLTN13190fig5.jpg|Figure 5D]]). Additional surfaces representing the boundaries between facies associations from the model of Deveugle et al.<ref name=Dvgl2011 /> were also extracted and similarly cropped; these define the distribution of facies associations present in each rock volume bounded by two clinoforms (i.e., clinothem) (cf. table 1 in Deveugle et al.<ref name=Dvgl2011 />). From distal to proximal, the modeled facies associations are prodelta [[mudstone]] (PD), distal delta-front heteroliths (dDF), proximal delta-front sandstones (pDF), and stream-mouth-bar sandstones (SMB) ([[:File:BLTN13190fig5.jpg|Figure 5D]]). Where facies associations pinch out, the facies association boundary surfaces were adjusted to coincide throughout the remainder of the model volume with either the top or base parasequence bounding surface. This ensures that the surface is defined across the entire model volume and is suitable for gridding.<ref name=Jckson2009 /> There are no faults within the model volume of 750 × 3000 × 6 m (2461 × 9843 × 20 ft). In a final step, isochore maps were generated between the top and base flooding surfaces and between facies association boundary surfaces and the base flooding surface. The base bounding surface was flattened, to mimic clinoform progradation over a flat, horizontal sea floor, and isochore maps were used to modify the geometries of the top bounding surface and facies association boundary surfaces above this horizontal base surface. As a result of flattening on the base bounding surface, the bounding surfaces from the existing model of Deveugle et al.<ref name=Dvgl2011 /> have been modified.

The parameters used to insert clinoforms into the model volume are summarized in Table 2. The delta lobe in parasequence 1.6 is approximately 8.1 km (5.03 mi) wide and 12.2 km (7.58 mi) long, giving a plan-view aspect ratio of 0.7,<ref name=Dvgl2011 /> comparable to values for lobes of the Pleistocene Lagniappe delta (after data in Kolla et al.;<ref name=Kll /> Roberts et al.<ref name=Rbrts2004 />) and the modern Wax Lake Delta lobe (after data in Wellner et al.<ref name=Wllnr2005 />) ([[:File:BLTN13190fig3.jpg|Figure 3C]]). These dimensions were likely smaller during the growth of the delta lobe, and it is assumed here that the lobe initiated with dimensions (''t_D'', ''t_s'') that were a third of those of the final preserved delta lobe, consistent in areal proportions to a single mouth-bar assemblage or jet-plume complex in the modern Wax Lake Delta lobe (after data in Wellner et al.<ref name=Wllnr2005 />). The length, ''L'', and spacing, ''S'', of clinoforms in depositional dip cross section were extracted from the bedding-diagram interpretations of Forster et al. <ref name=Frstr2004 /> ([[:File:BLTN13190fig6.jpg|Figure 6A]]), clinoform length and dip statistics of Enge et al.,<ref name=Eng2010 /> and the LIDAR data used to create the model of Enge and Howell.<ref name=EH2010 /> A database of clinoform lengths, dips, and spacings was compiled from these data sources, yielding frequency distributions from which the geometry or spatial arrangement of clinoforms that bound mouth-bar clinothems (sensu Bhattacharya<ref name=Bhttchry2006 />), or a trend in these parameters, can be extracted ([[:File:BLTN13190fig6.jpg|Figure 6B, C]]). The clinoform-modeling algorithm was used to build 31 clinoforms in the modeled volume of parasequence 1.6 ([[:File:BLTN13190fig7.jpg|Figure 7]]). For simplicity, clinoform spacing is fixed at 25 m (82 ft), which is the average value observed at outcrop ([[:File:BLTN13190fig6.jpg|Figure 6C]]). Heterogeneity at bed scale is recognized to be present but is not explicitly captured by surfaces in the model; rather, the effective petrophysical properties assigned to the facies associations (particularly the ratio of vertical-to-horizontal permeability) are modified to account for these.<ref name=Jckson2009 /><ref name=Dvgl2011 /><ref name=Grhm2015 /> A constant value of 2 was assigned to the clinoform shape-function exponent, ''P'' ([[:File:BLTN13190fig2.jpg|Figure 2E]]), to ensure that the clinoform dip angle is always in the range extracted from the data of Enge et al.<ref name=Eng2010 /> The initial clinoform insertion point, ''P_o'' ([[:File:BLTN13190fig4.jpg|Figure 4C]]), was qualitatively matched with a plan-view map of facies association belts at the top of parasequence 1.6 ([[:File:BLTN13190fig5.jpg|Figure 5D]]). The overall progradation direction for the clinoforms (''θ'') was assigned an [[azimuth]] of 274° relative to north, which corresponds to the interpreted progradation direction of the delta lobe in parasequence 1.6.<ref name=Dvgl2011 /> In a subsequent step, the facies association boundary surfaces extracted from the model of Deveugle et al.<ref name=Dvgl2011 /> were used to create facies association zones within each clinothem. Application of the clinoform-modeling algorithm yields a surface-based model measuring 750 × 3000 × 6 m (2461 × 9843 × 20 ft), which contains 95 surfaces: the top- and base-parasequence bounding surfaces, 31 clinoforms, and 62 facies-association boundary surfaces ([[:File:BLTN13190fig8.jpg|Figure 8]]).

The parameters used to insert clinoforms into the model volume are summarized in Table 2. The delta lobe in parasequence 1.6 is approximately 8.1 km (5.03 mi) wide and 12.2 km (7.58 mi) long, giving a plan-view aspect ratio of 0.7,<ref name=Dvgl2011 /> comparable to values for lobes of the Pleistocene Lagniappe delta (after data in Kolla et al.;<ref name=Kll /> Roberts et al.<ref name=Rbrts2004 />) and the modern Wax Lake Delta lobe (after data in Wellner et al.<ref name=Wllnr2005 />) ([[:File:BLTN13190fig3.jpg|Figure 3C]]). These dimensions were likely smaller during the growth of the delta lobe, and it is assumed here that the lobe initiated with dimensions (''t_D'', ''t_s'') that were a third of those of the final preserved delta lobe, consistent in areal proportions to a single mouth-bar assemblage or jet-plume complex in the modern Wax Lake Delta lobe (after data in Wellner et al.<ref name=Wllnr2005 />). The length, ''L'', and spacing, ''S'', of clinoforms in depositional dip cross section were extracted from the bedding-diagram interpretations of Forster et al. <ref name=Frstr2004 /> ([[:File:BLTN13190fig6.jpg|Figure 6A]]), clinoform length and dip statistics of Enge et al.,<ref name=Eng2010 /> and the LIDAR data used to create the model of Enge and Howell.<ref name=EH2010 /> A database of clinoform lengths, dips, and spacings was compiled from these data sources, yielding frequency distributions from which the geometry or spatial arrangement of clinoforms that bound mouth-bar clinothems (sensu Bhattacharya<ref name=Bhttchry2006 />), or a trend in these parameters, can be extracted ([[:File:BLTN13190fig6.jpg|Figure 6B, C]]). The clinoform-modeling algorithm was used to build 31 clinoforms in the modeled volume of parasequence 1.6 ([[:File:BLTN13190fig7.jpg|Figure 7]]). For simplicity, clinoform spacing is fixed at 25 m (82 ft), which is the average value observed at outcrop ([[:File:BLTN13190fig6.jpg|Figure 6C]]). Heterogeneity at bed scale is recognized to be present but is not explicitly captured by surfaces in the model; rather, the effective petrophysical properties assigned to the facies associations (particularly the ratio of vertical-to-horizontal permeability) are modified to account for these.<ref name=Jckson2009 /><ref name=Dvgl2011 /><ref name=Grhm2015 /> A constant value of 2 was assigned to the clinoform shape-function exponent, ''P'' ([[:File:BLTN13190fig2.jpg|Figure 2E]]), to ensure that the clinoform dip angle is always in the range extracted from the data of Enge et al.<ref name=Eng2010 /> The initial clinoform insertion point, ''P_o'' ([[:File:BLTN13190fig4.jpg|Figure 4C]]), was qualitatively matched with a plan-view map of facies association belts at the top of parasequence 1.6 ([[:File:BLTN13190fig5.jpg|Figure 5D]]). The overall progradation direction for the clinoforms (''θ'') was assigned an [[azimuth]] of 274° relative to north, which corresponds to the interpreted progradation direction of the delta lobe in parasequence 1.6.<ref name=Dvgl2011 /> In a subsequent step, the facies association boundary surfaces extracted from the model of Deveugle et al.<ref name=Dvgl2011 /> were used to create facies association zones within each clinothem. Application of the clinoform-modeling algorithm yields a surface-based model measuring 750 × 3000 × 6 m (2461 × 9843 × 20 ft), which contains 95 surfaces: the top- and base-parasequence bounding surfaces, 31 clinoforms, and 62 facies-association boundary surfaces ([[:File:BLTN13190fig8.jpg|Figure 8]]).

===Geological Setting===

===Geological Setting===

The clinoform-modeling algorithm is now applied to construct a model of the Upper Jurassic Sognefjord Formation reservoir in a fault-bounded sector of the Troll Field, offshore Norway ([[:File:BLTN13190fig12.jpg|Figure 12A, B]]). The Troll Field is a supergiant gas field that initially hosted about 40% of the total gas reserves on the Norwegian continental shelf and still contains ca. 1000 x 10⁹ S m³ (35 tcf) of gas.<ref>Norwegian Petroleum Directorate, 2013, [http://www.npd.no/en/Topics/Resource-accounts-and--analysis/Temaartikler/Resource-accounts/2011/ Positive resource accounts for the Norwegian shelf in 2011].</ref> The western and eastern parts of the Troll Field accumulation occur in different structures, Troll West and Troll East. The Sognefjord Formation is interpreted to record deposition in a mixed fluvial-, tide-, and wave-influenced delta system.<ref name=Dryr2005 /><ref name=Ptrno>Patruno, S., G. J. Hampson, C. A.-L. Jackson, and T. Dreyer, 2015, Clinoform geometry, geomorphology, facies character and stratigraphic architecture of a sand-rich subaqueous delta: Jurassic Sognefjord Formation, offshore Norway: Sedimentology, v. 62, no. 1, p. 350–388, doi: 10.1111/sed.12153.</ref> The formation is up to 170 m (558 ft) thick in the Troll Field and consists of five, vertically stacked regressive–transgressive successions bounded by major flooding surfaces (informally referred to as the 2-, 3-, 4-, 5- and 6-series in the reservoir; [[:File:BLTN13190fig12.jpg|Figure 12C]]).<ref name=Dryr2005 /> Each regressive–transgressive succession exhibits internal stratigraphic variability across the lateral extent of the reservoir, such that it can be interpreted as a sequence with constituent systems tracts and parasequences.<ref name=Dryr2005 /> The reservoir volume to be modeled contains seven, vertically stacked parasequences. The lower parasequences were deposited by regression of wave-dominated delta-fronts, whereas the upper parasequences comprise more tide-influenced delta-front deposits.<ref name=Dryr2005 />

The clinoform-modeling algorithm is now applied to construct a model of the Upper Jurassic Sognefjord Formation reservoir in a fault-bounded sector of the Troll Field, offshore Norway ([[:File:BLTN13190fig12.jpg|Figure 12A, B]]). The Troll Field is a supergiant gas field that initially hosted about 40% of the total gas reserves on the Norwegian continental shelf and still contains ca. 1000 x 10⁹ S m³ (35 tcf) of gas.<ref>Norwegian Petroleum Directorate, 2013, [http://www.npd.no/en/Topics/Resource-accounts-and--analysis/Temaartikler/Resource-accounts/2011/ Positive resource accounts for the Norwegian shelf in 2011].</ref> The western and eastern parts of the Troll Field accumulation occur in different structures, Troll West and Troll East. The Sognefjord Formation is interpreted to record deposition in a mixed fluvial-, tide-, and wave-influenced delta system.<ref name=Dryr2005 /><ref name=Ptrno>Patruno, S., G. J. Hampson, C. A.-L. Jackson, and T. Dreyer, 2015, Clinoform geometry, geomorphology, facies character and stratigraphic architecture of a sand-rich subaqueous delta: Jurassic Sognefjord Formation, offshore Norway: Sedimentology, v. 62, no. 1, p. 350–388, doi: 10.1111/sed.12153.</ref> The formation is up to 170 m (558 ft) thick in the Troll Field and consists of five, vertically stacked regressive–transgressive successions bounded by major flooding surfaces (informally referred to as the 2-, 3-, 4-, 5- and 6-series in the reservoir; [[:File:BLTN13190fig12.jpg|Figure 12C]]).<ref name=Dryr2005 /> Each regressive–transgressive succession exhibits internal stratigraphic variability across the [[lateral]] extent of the reservoir, such that it can be interpreted as a sequence with constituent systems tracts and parasequences.<ref name=Dryr2005 /> The reservoir volume to be modeled contains seven, vertically stacked parasequences. The lower parasequences were deposited by regression of wave-dominated delta-fronts, whereas the upper parasequences comprise more tide-influenced delta-front deposits.<ref name=Dryr2005 />

Reservoir zones in the Troll West accumulation are defined by alternating layers of fine-grained, micaceous sandstone and coarse-grained sandstone (informally referred to as m sands and c sands, respectively). The coarse-grained sandstones have higher porosity and permeability (hundreds to thousands of millidarcys) than the fine-grained, micaceous sandstones (tens to hundreds of millidarcys).<ref name=Gbbns /><ref name=Dryr2005 /> Each couplet of fine-grained, micaceous sandstone and overlying coarse-grained sandstones corresponds to the lower and upper part of a single delta-front parasequence.<ref name=Dryr2005 /> The 3-D seismic data image laterally extensive (up to 30 km [19 mi] along depositional strike), near-linear, north-northeast–south-southwest-trending clinoforms that dip west-northwestward at 1.5°–4°.<ref name=Dryr2005 /><ref name=Ptrno /> The structure of the Troll West reservoir is defined by two rotated fault blocks that formed after reservoir deposition, and the reservoir is further segmented by smaller postdepositional faults that trend west-northwest–east-southeast to north-northwest–south-southeast<ref name=Dryr2005 /> ([[:File:BLTN13190fig12.jpg|Figure 12B]]).

Reservoir zones in the Troll West accumulation are defined by alternating layers of fine-grained, micaceous sandstone and coarse-grained sandstone (informally referred to as m sands and c sands, respectively). The coarse-grained sandstones have higher porosity and permeability (hundreds to thousands of millidarcys) than the fine-grained, micaceous sandstones (tens to hundreds of millidarcys).<ref name=Gbbns /><ref name=Dryr2005 /> Each couplet of fine-grained, micaceous sandstone and overlying coarse-grained sandstones corresponds to the lower and upper part of a single delta-front parasequence.<ref name=Dryr2005 /> The 3-D seismic data image laterally extensive (up to 30 km [19 mi] along depositional strike), near-linear, north-northeast–south-southwest-trending clinoforms that dip west-northwestward at 1.5°–4°.<ref name=Dryr2005 /><ref name=Ptrno /> The structure of the Troll West reservoir is defined by two rotated fault blocks that formed after reservoir deposition, and the reservoir is further segmented by smaller postdepositional faults that trend west-northwest–east-southeast to north-northwest–south-southeast<ref name=Dryr2005 /> ([[:File:BLTN13190fig12.jpg|Figure 12B]]).

Troll West contains a thin oil column (11–26 m [36–85 ft]) that is exploited through the use of horizontal wells,<ref name=Dryr2005 /> the productivity of which is sensitive to the ratio of vertical-to-horizontal permeability (cf. Joshi<ref>Joshi, S. D., 1987, A review of horizontal well and drain hole technology: SPE Paper 16868, 17 p.</ref>). This ratio is predicted to be influenced by the calcite-cemented concretionary beds that are abundant in the Sognefjord Formation.<ref>Kantorowicz, J. D., I. D. Bryant, and J. M. Dawans, 1987, Controls on the geometry and distribution of carbonate cements in Jurassic sandstones: Bridport Sands, southern England and Viking Group, Troll Field, Norway, inJ. D. Marshall, ed., Diagenesis of sedimentary sequences: Geological Society, London, Special Publication 36, p. 103–118.</ref><ref>Lien, S. C., H. H. Haldorsen, and M. Manner, 1992, Horizontal wells: Still appealing in formations with discontinuous vertical permeability barriers?: Journal of Petroleum Technology, v. 44, no. 12, p. 1364–1370, doi: 10.2118/20962-PA.</ref><ref>Evensen, J. E., M. Skaug, and P. Goodyear, 1993, Production geological challenges of characterizing the thin oil rims in the Troll Field: OTC Paper 7172, Proceedings from the Offshore Technology Conference, Houston, Texas, USA, May 3–6, 1993, 12 p.</ref> These are present within delta-front parasequences, which are seismically imaged as clinoform sets, and along their bounding flooding surfaces.<ref name=Gbbns /><ref>Bakke, N. E., E. T. Ertresvåg, A. Næss, A. C. MacDonald, and L. M. Fält, 1996, Application of seismic data and sequence stratigraphy for constraining a stochastic model of calcite cementation: SPE Paper 35487, 13 p.</ref><ref name=Dryr2005 /><ref>Holgate, N. E., G. J. Hampson, C. A.-L. Jackson, and S. A. Petersen, 2014, [http://archives.datapages.com/data/bulletns/2014/12dec/BLTN13152/BLTN13152.html Constraining uncertainty in interpretation of seismically imaged clinoforms in deltaic reservoirs, Troll Field, Norwegian North Sea: Insights from forward seismic models of outcrop analogs]: AAPG Bulletin, v. 98, no. 12, p. 2629–2663, doi: 10.1306/05281413152.</ref><ref name=Ptrno /> The Jurassic Bridport Sand Formation, a close sedimentologic analog present onshore United Kingdom, contains similarly abundant calcite-cemented concretionary beds. These are observed at the outcrop to be laterally extensive (>80% areal coverage) along bedding planes and in a producing subsurface reservoir; their presence is marked by breaks in pressure and fluid saturation within seismically imaged clinoform sets.<ref>Hampson, G. J., J. E. Morris, and H. D. Johnson, 2014, Synthesis of time-stratigraphic relationships and their impact on hydrocarbon reservoir distribution and performance, Bridport Sand Formation, Wessex Basin, UK, inD. G. Smith, R. J. Bailey, P. M. Burgess, and A. J. Fraser, eds., Strata and time: Probing the gaps in our understanding: Geological Society, London, Special Publication 404, first published online on March 19, 2014, doi: 10.1144/SP404.2.</ref><ref>Morris, J. E., G. J. Hampson, and H. D. Johnson, 2006, A sequence stratigraphic model for an intensely bioturbated shallow-marine sandstone: The Bridport Sand Formation, Wessex basin, UK: Sedimentology, v. 53, no. 6, p. 1229–1263, doi: 10.1111/j.1365-3091.2006.00811.x.</ref> Thus it appears probable that permeability barriers and baffles in the form of calcite-cemented concretionary layers occur along clinoforms in the Troll Field reservoir and could influence drainage patterns and recovery from the thin oil zone;<ref name=Gbbns /> this may have been recognized previously and shown to impact on well test interpretations.<ref>Lien, S. C., K. Seines, S. O. Havig, and T. Kydland, 1991, The first long-term horizontal-well test in the Troll thin oil zone: Journal of Petroleum Technology, v. 43, no. 8, p. 914–973, doi: 10.2118/20715-PA.</ref><ref>Haug, B. T., 1992, The second long-term horizontal well test in Troll: Successful production from a 13-in. oil column with the well partly completed in the water zone: SPE Paper 24943, 10 p.</ref> However, to date, the heterogeneity associated with clinoforms has not been explicitly included in reservoir or flow-simulation models of the Sognefjord Formation in the Troll Field. Dilib et al.<ref name=Dlb>Dilib, F. A., M. D. Jackson, A. Mojaddam Zadeh, R. Aasheim, K. Årland, A. J. Gyllensten, and S. M. Erlandsen, 2015, Closed-loop feedback control in intelligent wells: Application to a heterogeneous, thin oil-rim reservoir in the North Sea: SPE Reservoir Evaluation and Engineering, v. 18, no. 1, 15 p., doi: 10.2118/159550-PA.</ref> created a sector model of the Sognefjord Formation (dimensions: 3200 × 750 × 150 m [10,499 × 2461 × 492 ft]) to investigate production optimization using intelligent wells for a range of uncertainty in geologic parameters and their model, extracted and refined from the existing full field geological model, was used here as the context in which to apply the clinoform-modeling algorithm.

Troll West contains a thin oil column (11–26 m [36–85 ft]) that is exploited through the use of [[horizontal well]]s,<ref name=Dryr2005 /> the productivity of which is sensitive to the ratio of vertical-to-horizontal permeability (cf. Joshi<ref>Joshi, S. D., 1987, A review of horizontal well and drain hole technology: SPE Paper 16868, 17 p.</ref>). This ratio is predicted to be influenced by the calcite-cemented concretionary beds that are abundant in the Sognefjord Formation.<ref>Kantorowicz, J. D., I. D. Bryant, and J. M. Dawans, 1987, Controls on the geometry and distribution of carbonate cements in Jurassic sandstones: Bridport Sands, southern England and Viking Group, Troll Field, Norway, inJ. D. Marshall, ed., Diagenesis of sedimentary sequences: Geological Society, London, Special Publication 36, p. 103–118.</ref><ref>Lien, S. C., H. H. Haldorsen, and M. Manner, 1992, Horizontal wells: Still appealing in formations with discontinuous vertical permeability barriers?: Journal of Petroleum Technology, v. 44, no. 12, p. 1364–1370, doi: 10.2118/20962-PA.</ref><ref>Evensen, J. E., M. Skaug, and P. Goodyear, 1993, Production geological challenges of characterizing the thin oil rims in the Troll Field: OTC Paper 7172, Proceedings from the Offshore Technology Conference, Houston, Texas, USA, May 3–6, 1993, 12 p.</ref> These are present within delta-front parasequences, which are seismically imaged as clinoform sets, and along their bounding flooding surfaces.<ref name=Gbbns /><ref>Bakke, N. E., E. T. Ertresvåg, A. Næss, A. C. MacDonald, and L. M. Fält, 1996, Application of seismic data and sequence stratigraphy for constraining a stochastic model of calcite cementation: SPE Paper 35487, 13 p.</ref><ref name=Dryr2005 /><ref>Holgate, N. E., G. J. Hampson, C. A.-L. Jackson, and S. A. Petersen, 2014, [http://archives.datapages.com/data/bulletns/2014/12dec/BLTN13152/BLTN13152.html Constraining uncertainty in interpretation of seismically imaged clinoforms in deltaic reservoirs, Troll Field, Norwegian North Sea: Insights from forward seismic models of outcrop analogs]: AAPG Bulletin, v. 98, no. 12, p. 2629–2663, doi: 10.1306/05281413152.</ref><ref name=Ptrno /> The Jurassic Bridport Sand Formation, a close sedimentologic analog present onshore United Kingdom, contains similarly abundant calcite-cemented concretionary beds. These are observed at the outcrop to be laterally extensive (>80% areal coverage) along bedding planes and in a producing subsurface reservoir; their presence is marked by breaks in pressure and fluid saturation within seismically imaged clinoform sets.<ref>Hampson, G. J., J. E. Morris, and H. D. Johnson, 2014, Synthesis of time-stratigraphic relationships and their impact on hydrocarbon reservoir distribution and performance, Bridport Sand Formation, Wessex Basin, UK, inD. G. Smith, R. J. Bailey, P. M. Burgess, and A. J. Fraser, eds., Strata and time: Probing the gaps in our understanding: Geological Society, London, Special Publication 404, first published online on March 19, 2014, doi: 10.1144/SP404.2.</ref><ref>Morris, J. E., G. J. Hampson, and H. D. Johnson, 2006, A sequence stratigraphic model for an intensely bioturbated shallow-marine sandstone: The Bridport Sand Formation, Wessex basin, UK: Sedimentology, v. 53, no. 6, p. 1229–1263, doi: 10.1111/j.1365-3091.2006.00811.x.</ref> Thus it appears probable that permeability barriers and baffles in the form of calcite-cemented concretionary layers occur along clinoforms in the Troll Field reservoir and could influence drainage patterns and recovery from the thin oil zone;<ref name=Gbbns /> this may have been recognized previously and shown to impact on well test interpretations.<ref>Lien, S. C., K. Seines, S. O. Havig, and T. Kydland, 1991, The first long-term horizontal-well test in the Troll thin oil zone: Journal of Petroleum Technology, v. 43, no. 8, p. 914–973, doi: 10.2118/20715-PA.</ref><ref>Haug, B. T., 1992, The second long-term horizontal well test in Troll: Successful production from a 13-in. oil column with the well partly completed in the water zone: SPE Paper 24943, 10 p.</ref> However, to date, the heterogeneity associated with clinoforms has not been explicitly included in reservoir or flow-simulation models of the Sognefjord Formation in the Troll Field. Dilib et al.<ref name=Dlb>Dilib, F. A., M. D. Jackson, A. Mojaddam Zadeh, R. Aasheim, K. Årland, A. J. Gyllensten, and S. M. Erlandsen, 2015, Closed-loop feedback control in intelligent wells: Application to a heterogeneous, thin oil-rim reservoir in the North Sea: SPE Reservoir Evaluation and Engineering, v. 18, no. 1, 15 p., doi: 10.2118/159550-PA.</ref> created a sector model of the Sognefjord Formation (dimensions: 3200 × 750 × 150 m [10,499 × 2461 × 492 ft]) to investigate production optimization using intelligent wells for a range of uncertainty in geologic parameters and their model, extracted and refined from the existing full field geological model, was used here as the context in which to apply the clinoform-modeling algorithm.

===Model Construction===

===Model Construction===