Paul "Mitch" Harris hails from West Virginia University where he earned his BS and MS in Geology. Mitch migrated to the University of Miami, for his PhD where he focused on the sequence of modern sediments. Mitch joined Getty Oil briefly then Gulf Oil until they merged with Chevron and Mitch moved to California. Mitch has spent his career thus far linking modern and ancient systems and has worked everything from the Permian Basin to Super Giants like Tengiz, while making countless trips to the modern to teach, ask questions, observe and apply concepts to the subsurface. Mitch is adjunct professor at the University of Miami and Rice. In 2010-2011, Mitch served as President of SEPM, and he’s been awarded SEPM Honorary Membership, Honorary Life Award from PBSEPM, AAPG Honorary Membership, Wallace E. Pratt Memorial Award, Robert H.Dott, Sr. Memorial Award twice and John W. Shelton Search & Discovery Award.
Paul "Mitch" Harris hails from West Virginia University where he earned his BS and MS in Geology. Mitch migrated to the University of Miami, for his PhD where he focused on the sequence of modern sediments. Mitch joined Getty Oil briefly then Gulf Oil until they merged with Chevron and Mitch moved to California. Mitch has spent his career thus far linking modern and ancient systems and has worked everything from the Permian Basin to Super Giants like Tengiz, while making countless trips to the modern to teach, ask questions, observe and apply concepts to the subsurface. Mitch is adjunct professor at the University of Miami and Rice. In 2010-2011, Mitch served as President of SEPM, and he’s been awarded SEPM Honorary Membership, Honorary Life Award from PBSEPM, AAPG Honorary Membership, Wallace E. Pratt Memorial Award, Robert H.Dott, Sr. Memorial Award twice and John W. Shelton Search & Discovery Award.
Panel_14392
Panel_14392
1:15 PM
5:05 PM
1:15 p.m.
Introductory Remarks
Four Seasons Ballroom 1
Panel_15765
Panel_15765
1:15 PM
12:00 AM
1:20 p.m.
Characterizing Carbonate Grainstone Geobodies
Four Seasons Ballroom 1
By C. Kerans
Oolitic, peloidal, and skeletal grainstones are a key element of carbonate reservoir heterogeneity in many ramp crest and shelf-margin settings. Imaging the aerial and vertical (stratigraphic) distribution of grainstone geobodies is essential for understanding distribution of primary and secondary porosity and fluid flow pathways in reservoirs like the prolific San Andres/Grayburg and Horseshoe Atoll trends of the Permian Basin. Typical grainstone elements are contained within individual depositional cycles of 2-10 m thickness. When stacked vertically there is an opportunity to image these seismically, but commonly intermediate-scale landward or seaward translation of facies tracts keeps porosity zones thin and distributed, thus below seismic resolution. Modern examples like the well-documented Joulter’s Cay complex described by Harris (1979) highlight the complexity of these deposits in both time and space, and detailed outcrop mapping of successive intra-cycle bar complexes demonstrates a range of dip-extents rarely > 1 km. Outcrop and subsurface studies of Paleozoic (14) and Mesozoic (7) outcrops and reservoirs (each averaging 10 discrete grainstone geobodies) highlight differences between land-attached and shelf-edge complexes. Land-attached grainstone geobodies include foreshore-shoreface, lagoon-inlet-barrier, and sharp-based shoreface. Fair-weather and storm waves provide current energy; wind-driven longshore currents are secondary. Shelf-edge grainstones include back-reef aprons (skeletal only), tidal bars (oolitic), mixed tide-wave systems, and wind-wave bars. The most extensive ancient examples have a strong tidal influence, stable tectonics and minimal eustatic signal. The presence of a shelf-interior lagoon to allow tidal exchange is critical, and persistent longshore or trade-wind current dominates some settings. Tide-dominated grainstones show complex paleocurrents with distinct ebb-domination, large (>1m) bedforms, and oolitic composition. The Ambergris shoal (Caicos) is an analog for low-energy grainstones with maximum 10-20 cm cross-bed size such as the Jurassic Arab D. Storm-ridge wave-dominated grainstones like the shelf-crest of the Capitan system and the caprinid beaches of the Stuart City trend are characteristically coarse-grained, have significant vadose profiles, and are distinctly strike-elongate and dip limited. Tuning next-generation stochastic models to these depositional assemblages should constrain the universe of realizations.
Oolitic, peloidal, and skeletal grainstones are a key element of carbonate reservoir heterogeneity in many ramp crest and shelf-margin settings. Imaging the aerial and vertical (stratigraphic) distribution of grainstone geobodies is essential for understanding distribution of primary and secondary porosity and fluid flow pathways in reservoirs like the prolific San Andres/Grayburg and Horseshoe Atoll trends of the Permian Basin. Typical grainstone elements are contained within individual depositional cycles of 2-10 m thickness. When stacked vertically there is an opportunity to image these seismically, but commonly intermediate-scale landward or seaward translation of facies tracts keeps porosity zones thin and distributed, thus below seismic resolution. Modern examples like the well-documented Joulter’s Cay complex described by Harris (1979) highlight the complexity of these deposits in both time and space, and detailed outcrop mapping of successive intra-cycle bar complexes demonstrates a range of dip-extents rarely > 1 km. Outcrop and subsurface studies of Paleozoic (14) and Mesozoic (7) outcrops and reservoirs (each averaging 10 discrete grainstone geobodies) highlight differences between land-attached and shelf-edge complexes. Land-attached grainstone geobodies include foreshore-shoreface, lagoon-inlet-barrier, and sharp-based shoreface. Fair-weather and storm waves provide current energy; wind-driven longshore currents are secondary. Shelf-edge grainstones include back-reef aprons (skeletal only), tidal bars (oolitic), mixed tide-wave systems, and wind-wave bars. The most extensive ancient examples have a strong tidal influence, stable tectonics and minimal eustatic signal. The presence of a shelf-interior lagoon to allow tidal exchange is critical, and persistent longshore or trade-wind current dominates some settings. Tide-dominated grainstones show complex paleocurrents with distinct ebb-domination, large (>1m) bedforms, and oolitic composition. The Ambergris shoal (Caicos) is an analog for low-energy grainstones with maximum 10-20 cm cross-bed size such as the Jurassic Arab D. Storm-ridge wave-dominated grainstones like the shelf-crest of the Capitan system and the caprinid beaches of the Stuart City trend are characteristically coarse-grained, have significant vadose profiles, and are distinctly strike-elongate and dip limited. Tuning next-generation stochastic models to these depositional assemblages should constrain the universe of realizations.
Panel_14757
Panel_14757
1:20 PM
1:40 PM
1:40 p.m.
Geostatistical Modeling Trends for Oolitic Tidal Sand Shoals
Four Seasons Ballroom 1
By J. Rush, E. C. Rankey
To assess prospective modeling parameters and trends for oolitic tidal sand shoals, this study examines the cycle-scale architecture of the mobile, oolitic tidal bar belt at Schooner Cays, Bahamas. Process-based, stratigraphic trends are captured in quantitative, geocellular models of the shoal from analyses of satellite imagery, 2-D high-frequency seismic (Chirp), and sediment cores. Observations reveal recurring trends in geomorphic shapes and sedimentation patterns across this oolitic bar belt. For example, longitudinal tidal sand ridges repetitively extend up to 8 km along depositional dip gradually transforming backward into channel-bound, compound barforms consisting of linear, parabolic, and shoulder bars before terminating into a laterally extensive (<10 km), strike-elongate, sand sheet. Detailed geologic models of the shoal integrate facies probability curves, facies probability maps, facies probability cubes, bar and channel centerlines, locally varying azimuthal trends, satellite imagery, 2-D seismic, and core. To enhance confidence in this approach, we first quantify and demonstrate spatial trends in grain size, type, sorting, and barform orientation across the ooid shoal. A geocellular facies model—conditioned to multiple 3-D trends across the shoal—is built from which end-member barforms are extracted for 3-D visualization, quantitative analyses, and validation of geostatistical trends at different scales. Co-rendering of satellite imagery and bathymetric grids reveals that barforms are largely low-angle (<6°) and laterally gradational with adjacent shoal environments. As such, sequential indicator simulation (SIS) techniques are preferred. Facies proportion curves are well-ordered with respect to water depth facilitating distribution of upward-shallowing trends within barforms across the shoal. Inclusion of geometrical trends, anisotropic variograms, and 3-D facies probability grids during SIS generates gradational lithofacies tracts that are appropriately juxtaposed and consistently elongate parallel to bar crests and channels. Analyses of bootstrapped end-member barforms validates modeling techniques and reveals locally predicted facies distributions consistent with field and core observations. Although the modeling trends and methods presented here are for a specific style of modern oolitic sand shoal, similar trends might be discovered for ancient oolitic reservoirs through integrative studies of core and advanced seismic attributes.
To assess prospective modeling parameters and trends for oolitic tidal sand shoals, this study examines the cycle-scale architecture of the mobile, oolitic tidal bar belt at Schooner Cays, Bahamas. Process-based, stratigraphic trends are captured in quantitative, geocellular models of the shoal from analyses of satellite imagery, 2-D high-frequency seismic (Chirp), and sediment cores. Observations reveal recurring trends in geomorphic shapes and sedimentation patterns across this oolitic bar belt. For example, longitudinal tidal sand ridges repetitively extend up to 8 km along depositional dip gradually transforming backward into channel-bound, compound barforms consisting of linear, parabolic, and shoulder bars before terminating into a laterally extensive (<10 km), strike-elongate, sand sheet. Detailed geologic models of the shoal integrate facies probability curves, facies probability maps, facies probability cubes, bar and channel centerlines, locally varying azimuthal trends, satellite imagery, 2-D seismic, and core. To enhance confidence in this approach, we first quantify and demonstrate spatial trends in grain size, type, sorting, and barform orientation across the ooid shoal. A geocellular facies model—conditioned to multiple 3-D trends across the shoal—is built from which end-member barforms are extracted for 3-D visualization, quantitative analyses, and validation of geostatistical trends at different scales. Co-rendering of satellite imagery and bathymetric grids reveals that barforms are largely low-angle (<6°) and laterally gradational with adjacent shoal environments. As such, sequential indicator simulation (SIS) techniques are preferred. Facies proportion curves are well-ordered with respect to water depth facilitating distribution of upward-shallowing trends within barforms across the shoal. Inclusion of geometrical trends, anisotropic variograms, and 3-D facies probability grids during SIS generates gradational lithofacies tracts that are appropriately juxtaposed and consistently elongate parallel to bar crests and channels. Analyses of bootstrapped end-member barforms validates modeling techniques and reveals locally predicted facies distributions consistent with field and core observations. Although the modeling trends and methods presented here are for a specific style of modern oolitic sand shoal, similar trends might be discovered for ancient oolitic reservoirs through integrative studies of core and advanced seismic attributes.
Panel_14759
Panel_14759
1:40 PM
2:00 PM
2:00 p.m.
Accommodation Space on an Isolated Carbonate Platform — Patterns and Implications
Four Seasons Ballroom 1
By S. J. Purkis, P. Harris
Great Bahama Bank (GBB) is ‘the’ modern example of a flat-topped, isolated carbonate platform. It is a major modern location of non-skeletal carbonate deposition that stands behind much of our understanding of modern processes of carbonate sedimentation and is the basis for geological models that serve as reservoir analogs. GBB provides valuable insight into the extent and patterns of sediment fill of accommodation space across the platform top. Satellite imagery (Landsat TM and ETM+) and an extensive set of water-depth measurements (n = 5,723) were used to map bathymetry across GBB. Analysis of the resulting digital terrain model (DTM) reveals the maximum variation in depth-elevation over this vast (>100,000 sq. km) platform extends from the -30 m platform break to the highest Pleistocene eolianite ridge of 63 m on Cat Island. It is noteworthy, however, that although islands atop the GBB are numerous (n = 1,427) they occupy only 7.5%, or 7,716 sq. km, of the platform-top. Since islands represent the portion of the platform where accommodation has been overfilled, their rarity emphasizes the challenges to filling accommodation space across such a large platform despite the diverse grain factories producing carbonate detritus atop GBB (mud precipitation through whitings, ooids along the platform margins, skeletal sediments, and non-skeletal grains such as pellets, peloids and aggregate grains). It should be noted that aerial coverage of the GBB’s islands is in fact an overestimate of overfilled accommodation; although many Holocene islands are built from storm ridge and eolianite deposits, the contribution of sub-tidal facies deposited during higher sea level are also important structuring components to Pleistocene islands. Considering the bathymetric variation of the GBB, the DTM brings to light the fact that only 7% (7,237 sq. km) of the awash platform has aggraded to sea level in the form of sand shoals or mud flats (<1 m water depth) and therefore the majority of available accommodation (~87,600 sq. km or > 85% of the platform top) remains under-filled with sediment. Areas of filled accommodation mostly extend platformward from the westerly coastlines of islands, which in turn are preferentially distributed along the eastern (windward) margin of the GBB. The bathymetric patterns highlight the irregular filling of accommodation space and graphically emphasize the challenges of correlating depositional cycles of variable thickness across a platform.
Great Bahama Bank (GBB) is ‘the’ modern example of a flat-topped, isolated carbonate platform. It is a major modern location of non-skeletal carbonate deposition that stands behind much of our understanding of modern processes of carbonate sedimentation and is the basis for geological models that serve as reservoir analogs. GBB provides valuable insight into the extent and patterns of sediment fill of accommodation space across the platform top. Satellite imagery (Landsat TM and ETM+) and an extensive set of water-depth measurements (n = 5,723) were used to map bathymetry across GBB. Analysis of the resulting digital terrain model (DTM) reveals the maximum variation in depth-elevation over this vast (>100,000 sq. km) platform extends from the -30 m platform break to the highest Pleistocene eolianite ridge of 63 m on Cat Island. It is noteworthy, however, that although islands atop the GBB are numerous (n = 1,427) they occupy only 7.5%, or 7,716 sq. km, of the platform-top. Since islands represent the portion of the platform where accommodation has been overfilled, their rarity emphasizes the challenges to filling accommodation space across such a large platform despite the diverse grain factories producing carbonate detritus atop GBB (mud precipitation through whitings, ooids along the platform margins, skeletal sediments, and non-skeletal grains such as pellets, peloids and aggregate grains). It should be noted that aerial coverage of the GBB’s islands is in fact an overestimate of overfilled accommodation; although many Holocene islands are built from storm ridge and eolianite deposits, the contribution of sub-tidal facies deposited during higher sea level are also important structuring components to Pleistocene islands. Considering the bathymetric variation of the GBB, the DTM brings to light the fact that only 7% (7,237 sq. km) of the awash platform has aggraded to sea level in the form of sand shoals or mud flats (<1 m water depth) and therefore the majority of available accommodation (~87,600 sq. km or > 85% of the platform top) remains under-filled with sediment. Areas of filled accommodation mostly extend platformward from the westerly coastlines of islands, which in turn are preferentially distributed along the eastern (windward) margin of the GBB. The bathymetric patterns highlight the irregular filling of accommodation space and graphically emphasize the challenges of correlating depositional cycles of variable thickness across a platform.
Panel_14764
Panel_14764
2:00 PM
2:20 PM
2:20 p.m.
Influence of Neo-Tectonic Activity in the Cuban Fold and Thrust Belt on the Slope and Margin Failures of Cay Sal and Great Bahama Bank
Four Seasons Ballroom 1
By G. P. Eberli, D. Kula, A. Jo, J. L. Massaferro, T. Lüdmann, C. Betzler
The Bahamian archipelago is considered tectonically inactive but a fold growth analysis on the most distal anticline of the Cuban fold and thrust belt indicates continuous shortening throughout the Neogene. In addition, several structural elements around of Cay Sal Bank document recent movements. Deep-rooted faults with both thrust and wrench fault characteristics separate the platform from the adjacent basin. Two of these faults reach the seafloor, forming 30 km long and 50 m high scars on the seafloor. Anticlines that are dissected by faults display Holocene fold-growth strata. Both these features, together with recent earthquakes, document the neo-tectonic activity in this part of the archipelago. Multi-channel seismic and multi-beam data reveal for the first time a tectonic influence on the slope sedimentation of Great Bahama Bank (GBB) and Cay Sal Bank (CSB). Neo-tectonics does not change the general bank morphology but it is reflected in the slope development. GBB with its 450 km long margin that is nearly perpendicular to the Cuban fold and thrust belt displays the decreasing tectonic influence from south to north. In the proximity of the fold and thrust belt, large margin collapse features and associated mass transport complexes are common. Away from plate boundary only slope failures are observed that are likely not triggered by tectonic processes. Along eastern CSB the neo-tectonic activity is recognized in lateral displacements of slope canyons and vertical scars on the sea floor. On the north and eastern side of CSB, multichannel seismic data display deep-rooted faults terminating at various stratigraphic horizons, documenting the ongoing deformation related to the Cuban fold and thrust belt. Some of the faults displace the seafloor on the slope and in the basin. Bathymetric maps of the slopes display asymmetric canyons that are oriented oblique to smaller slope gullies and are in some places displaced laterally. This canyon geometry is interpreted to reflect an underlying fault pattern. The connection of faults to large mass wasting events is seen on seismic data where chaotic slump units terminate against buried faults. These slow tectonic movements in the Cuban fold and thrust belt are not enough to change overall platform architecture but influences the type and location of slope and margin failure.
The Bahamian archipelago is considered tectonically inactive but a fold growth analysis on the most distal anticline of the Cuban fold and thrust belt indicates continuous shortening throughout the Neogene. In addition, several structural elements around of Cay Sal Bank document recent movements. Deep-rooted faults with both thrust and wrench fault characteristics separate the platform from the adjacent basin. Two of these faults reach the seafloor, forming 30 km long and 50 m high scars on the seafloor. Anticlines that are dissected by faults display Holocene fold-growth strata. Both these features, together with recent earthquakes, document the neo-tectonic activity in this part of the archipelago. Multi-channel seismic and multi-beam data reveal for the first time a tectonic influence on the slope sedimentation of Great Bahama Bank (GBB) and Cay Sal Bank (CSB). Neo-tectonics does not change the general bank morphology but it is reflected in the slope development. GBB with its 450 km long margin that is nearly perpendicular to the Cuban fold and thrust belt displays the decreasing tectonic influence from south to north. In the proximity of the fold and thrust belt, large margin collapse features and associated mass transport complexes are common. Away from plate boundary only slope failures are observed that are likely not triggered by tectonic processes. Along eastern CSB the neo-tectonic activity is recognized in lateral displacements of slope canyons and vertical scars on the sea floor. On the north and eastern side of CSB, multichannel seismic data display deep-rooted faults terminating at various stratigraphic horizons, documenting the ongoing deformation related to the Cuban fold and thrust belt. Some of the faults displace the seafloor on the slope and in the basin. Bathymetric maps of the slopes display asymmetric canyons that are oriented oblique to smaller slope gullies and are in some places displaced laterally. This canyon geometry is interpreted to reflect an underlying fault pattern. The connection of faults to large mass wasting events is seen on seismic data where chaotic slump units terminate against buried faults. These slow tectonic movements in the Cuban fold and thrust belt are not enough to change overall platform architecture but influences the type and location of slope and margin failure.
Panel_14758
Panel_14758
2:20 PM
2:40 PM
2:40 p.m.
Break
Four Seasons Ballroom 1
Panel_15766
Panel_15766
2:40 PM
12:00 AM
3:25 p.m.
Comparative Geomorphology and Dynamics of Holocene Isolated Carbonate Buildups, South China Sea
Four Seasons Ballroom 1
By E. C. Rankey
Carbonate strata form important reservoirs in southeast Asia, including Eocene-Miocene isolated buildups. Although seismic data from some platforms illustrate internal geometries such as platformward progradation of reef sand aprons, in most, such direct facies indicators are absent. In such scenarios, analogs provide both conceptual models and data to constrain facies dimensions, orientation, and configuration. The overall objective of this study is to use remote sensing data to systematically examine and quantify spatial facies patterns of Holocene isolated carbonate buildups (ICB) in the South China Sea. The fundamental data for the study are high-resolution (<2.4 m2 multispectral, 0.6 m2 panchromatic) remote sensing images of 27 ICB. Each ICB is captured by at least one image collected between 2003 and 2014; 11 ICB include two or more temporally distinct images that permit assessing temporal changes on these platforms. Analysis of remote sensing data of ICB of the South China Sea includes platforms ranging in size from 5 – 195 km2, and include circular, ovoid, and elongate shapes. The mean orientation of the long axis for ICB of both the Spratly (73°) and the Paracel (96°) chains are slightly different, probably related to tectonic framework. ICB facies bodies include reefs and reef sand aprons that are non-uniformly distributed within and among platforms. Platforms range from incipiently drowned to almost fully aggraded, and include reef sand aprons and reefs that can exceed 1500 m width. Despite the variability, a pronounced trend of marked asymmetry of the spatial distribution reef sand aprons is evident: 89% of ICB include the widest reef sand apron on the north- or west-facing flank. These systems are not static. Although some ICB show no changes between multi-temporal images, several ICB illustrate rather pronounced changes; in one case (Mischief), reef-derived debris migrated over 300 m towards the platform interior in 8 years (2004-2012). A database of processes (characteristics of waves, tides, currents, and winds, for example) provides a process-based understanding of the genesis and potential evolution of these systems. These results provide conceptual models and data that could be used as input on facies attributes for geologic models.
Carbonate strata form important reservoirs in southeast Asia, including Eocene-Miocene isolated buildups. Although seismic data from some platforms illustrate internal geometries such as platformward progradation of reef sand aprons, in most, such direct facies indicators are absent. In such scenarios, analogs provide both conceptual models and data to constrain facies dimensions, orientation, and configuration. The overall objective of this study is to use remote sensing data to systematically examine and quantify spatial facies patterns of Holocene isolated carbonate buildups (ICB) in the South China Sea. The fundamental data for the study are high-resolution (<2.4 m2 multispectral, 0.6 m2 panchromatic) remote sensing images of 27 ICB. Each ICB is captured by at least one image collected between 2003 and 2014; 11 ICB include two or more temporally distinct images that permit assessing temporal changes on these platforms. Analysis of remote sensing data of ICB of the South China Sea includes platforms ranging in size from 5 – 195 km2, and include circular, ovoid, and elongate shapes. The mean orientation of the long axis for ICB of both the Spratly (73°) and the Paracel (96°) chains are slightly different, probably related to tectonic framework. ICB facies bodies include reefs and reef sand aprons that are non-uniformly distributed within and among platforms. Platforms range from incipiently drowned to almost fully aggraded, and include reef sand aprons and reefs that can exceed 1500 m width. Despite the variability, a pronounced trend of marked asymmetry of the spatial distribution reef sand aprons is evident: 89% of ICB include the widest reef sand apron on the north- or west-facing flank. These systems are not static. Although some ICB show no changes between multi-temporal images, several ICB illustrate rather pronounced changes; in one case (Mischief), reef-derived debris migrated over 300 m towards the platform interior in 8 years (2004-2012). A database of processes (characteristics of waves, tides, currents, and winds, for example) provides a process-based understanding of the genesis and potential evolution of these systems. These results provide conceptual models and data that could be used as input on facies attributes for geologic models.
Panel_14760
Panel_14760
3:25 PM
3:45 PM
3:45 p.m.
Changing Carbonate Sedimentation During the Holocene Transgression: New Providence Platform, Bahamas
Four Seasons Ballroom 1
By K. L. Jackson, G. P. Eberli, P. Harris, D. F. McNeill
The sedimentary record of New Providence Platform (NPP) and the Exumas windward margin portions of Great Bahama Bank reveals complex, shifting sediment patterns during the Holocene sea-level transgression. Understanding these patterns provides a more robust analog for interpreting and correlating depositional cycles in subsurface examples. Sea-level changes drive sediment dynamics in shallow-water carbonate settings, producing facies indicative of relative sea-level positions and making them excellent sea-level archives. Rising sea level and concomitant sedimentation constantly change the energy distribution and locations of sedimentation and erosion. A shift in the energy balance across NPP during the Holocene transgression is recorded in the coarsening-upwards sedimentary succession documented in the platform interior (Yellow Banks). This succession indicates an increase in energy with increasing water depth, changing the once restricted platform to high-energy, open-marine conditions (i.e. change from muddy to high-energy, grapestone/skeletal sediments). The preservation potential varies from the platform interior (highest preservation potential) eastwards towards the outermost Exuma Cays platform margin (poorest preservation potential). The Exumas windward platform margin features islands dissected by high-energy channels and ooid shoals. Pleistocene antecedent topography acts as a barrier to the erosion caused by the Holocene transgression and also provides a template for complex Holocene carbonate sediment deposition and accretion. Eastward of the islands, very little Holocene sediment is preserved; sediments on this sloping margin are either transported towards the platform or into Exuma Sound. In many places, the sloping outer margin is eroded down to the Pleistocene surface. Locally, the windward margins of the islands contain steep, eroding sea cliffs and small relicts of older Holocene eolianites. On leeward sides of the islands towards the platform interior, the erosion is minimal and a more complete record of Holocene sedimentation is commonly present. The Pleistocene islands mark the boundary between low and high sediment preservation. In addition, in the present-day energy situation, they are also focusing the tidal currents, producing high-energy environments with increased sedimentation. These sediments are deposited in ooid shoals or as accreting beaches on both the open-ocean and the bankside of the Pleistocene islands.
The sedimentary record of New Providence Platform (NPP) and the Exumas windward margin portions of Great Bahama Bank reveals complex, shifting sediment patterns during the Holocene sea-level transgression. Understanding these patterns provides a more robust analog for interpreting and correlating depositional cycles in subsurface examples. Sea-level changes drive sediment dynamics in shallow-water carbonate settings, producing facies indicative of relative sea-level positions and making them excellent sea-level archives. Rising sea level and concomitant sedimentation constantly change the energy distribution and locations of sedimentation and erosion. A shift in the energy balance across NPP during the Holocene transgression is recorded in the coarsening-upwards sedimentary succession documented in the platform interior (Yellow Banks). This succession indicates an increase in energy with increasing water depth, changing the once restricted platform to high-energy, open-marine conditions (i.e. change from muddy to high-energy, grapestone/skeletal sediments). The preservation potential varies from the platform interior (highest preservation potential) eastwards towards the outermost Exuma Cays platform margin (poorest preservation potential). The Exumas windward platform margin features islands dissected by high-energy channels and ooid shoals. Pleistocene antecedent topography acts as a barrier to the erosion caused by the Holocene transgression and also provides a template for complex Holocene carbonate sediment deposition and accretion. Eastward of the islands, very little Holocene sediment is preserved; sediments on this sloping margin are either transported towards the platform or into Exuma Sound. In many places, the sloping outer margin is eroded down to the Pleistocene surface. Locally, the windward margins of the islands contain steep, eroding sea cliffs and small relicts of older Holocene eolianites. On leeward sides of the islands towards the platform interior, the erosion is minimal and a more complete record of Holocene sedimentation is commonly present. The Pleistocene islands mark the boundary between low and high sediment preservation. In addition, in the present-day energy situation, they are also focusing the tidal currents, producing high-energy environments with increased sedimentation. These sediments are deposited in ooid shoals or as accreting beaches on both the open-ocean and the bankside of the Pleistocene islands.
Panel_14763
Panel_14763
3:45 PM
4:05 PM
4:05 p.m.
New Approaches for Diagenetic Characterization of Carbonate Reservoirs: Examples From Tengiz Field, Republic of Kazakhstan
Four Seasons Ballroom 1
By T. Playton, J. W. Bishop*, N. Hurley, C. Miller, M. Seibel, P. Harris, D. Katz, J. Collins
Characterizing diagenesis, in addition to facies arrangements and stratigraphic architecture, is critical for predicting the distribution of reservoir quality in many carbonate reservoirs. Carbonate diagenetic histories are often extremely complex, reflecting syndepositional to deep burial processes with multiple superimposed cementation and dissolution events. Traditionally, these records are captured in paragenetic charts that focus only on the presence of the various phases in a rock but lack linkage to reservoir quality. We here propose an approach for carbonate diagenetic characterization that, in addition to traditional documentation of the paragenetic sequence of cements and pore types, also 1) distills the multifaceted paragenesis into the event(s) that most impacted present-day reservoir quality (Key Paragenetic Step, KPS); 2) graphically depicts the starting point, diagenetic path, and end-product for a particular rock (Paragenogram); and 3) links to the distribution of reservoir quality (flow units) through integration of diagenetic profiles, cumulative-thickness plots, depositional facies, and sequence stratigraphy. To demonstrate this approach, we present examples from carbonate margin and slope facies of the Paleozoic Tengiz field in the Republic of Kazakhstan, where a complex diagenetic history heavily impacted matrix reservoir quality and non-matrix flow characteristics. The dataset consists of 16 cores with thin sections that sample margin grainstone/boundstone-, upper slope boundstone-, middle slope breccia/grainstone-, and lower slope grainstone/mudstone facies assemblages. Using our new approach, we developed a framework that ties diagenetic styles to resulting rock types and improves the linkages between depositional facies, diagenetic overprints, volumetrically significant pore families, and the origins and distribution of enhanced matrix reservoir quality. For example, this work underscored the importance of burial dissolution and its link to improved matrix porosity, permeability, and flow behavior. These findings provide geological context to better understand MICP-derived pore throat data, porosity-permeability distributions, and vertical flow behavior along the borehole, as well as valuable input for log-based Petrophysical Rock Typing.
Characterizing diagenesis, in addition to facies arrangements and stratigraphic architecture, is critical for predicting the distribution of reservoir quality in many carbonate reservoirs. Carbonate diagenetic histories are often extremely complex, reflecting syndepositional to deep burial processes with multiple superimposed cementation and dissolution events. Traditionally, these records are captured in paragenetic charts that focus only on the presence of the various phases in a rock but lack linkage to reservoir quality. We here propose an approach for carbonate diagenetic characterization that, in addition to traditional documentation of the paragenetic sequence of cements and pore types, also 1) distills the multifaceted paragenesis into the event(s) that most impacted present-day reservoir quality (Key Paragenetic Step, KPS); 2) graphically depicts the starting point, diagenetic path, and end-product for a particular rock (Paragenogram); and 3) links to the distribution of reservoir quality (flow units) through integration of diagenetic profiles, cumulative-thickness plots, depositional facies, and sequence stratigraphy. To demonstrate this approach, we present examples from carbonate margin and slope facies of the Paleozoic Tengiz field in the Republic of Kazakhstan, where a complex diagenetic history heavily impacted matrix reservoir quality and non-matrix flow characteristics. The dataset consists of 16 cores with thin sections that sample margin grainstone/boundstone-, upper slope boundstone-, middle slope breccia/grainstone-, and lower slope grainstone/mudstone facies assemblages. Using our new approach, we developed a framework that ties diagenetic styles to resulting rock types and improves the linkages between depositional facies, diagenetic overprints, volumetrically significant pore families, and the origins and distribution of enhanced matrix reservoir quality. For example, this work underscored the importance of burial dissolution and its link to improved matrix porosity, permeability, and flow behavior. These findings provide geological context to better understand MICP-derived pore throat data, porosity-permeability distributions, and vertical flow behavior along the borehole, as well as valuable input for log-based Petrophysical Rock Typing.
Panel_14761
Panel_14761
4:05 PM
4:25 PM
4:25 p.m.
Reservoir Quality Variations in the Oligocene Kirkuk Group in Southeast Kurdistan, Iraq
Four Seasons Ballroom 1
By J. Hsieh
This abstract is submitted to the session in celebration of the career of Paul “Mitch” Harris. Mitch has taught me that to understand carbonates, you need to investigate all aspects of its depositional and diagenetic history by using core, well logs, seismic interpretation, biostratigraphy, geochemistry, petrography, outcrop analogs and anything else that you can. This project is my attempt to apply his teachings in order to understand the complex reservoir. Significant oil and gas discoveries in the Topkhana and Kurdamir blocks of southeast Kurdistan are primarily contained within the Oligocene Kirkuk group. This group is regionally composed of middle ramp foraminiferal and red algae grainstones as well as coral boundstones/rudstones that likely form small bioherms. Reservoir quality is highly dependent on both the original depositional facies as well as the overprint of dolomitization. Predicting the spatial distribution of the best reservoir quality is challenging. Earlier studies (Hsieh et al., 2013) suggest that the best reservoir rock quality occurs where there is intense dolomitization along with dissolution of the foraminiferal tests. Original intergranular porosity was often occluded by marine cement and thus, non-dolomitized grainstones were considered poorer quality and not the primary target. Based on Sr-isotope geochemistry, dolomitization was shown to occur primarily in the earliest Miocene. This suggested a “top down” dolomitization of the Kirkuk Group where the dolomite geobody would be located beneath the dolomitizing fluid body. Early interpretation of the 3D seismic data supported this hypothesis. However, recently collected cores provided not only a down-dip limit to the dolomitization front, but also added a twist in the reservoir quality story. Dolomitization only improved reservoir quality if the process was complete while partially dolomitized rocks were in fact poorer quality than non-dolomitized rocks. Additionally, coral boundstone and rudstones that seem to preserve the depositional porosity have similar flow properties as the best dolomitized rock. The spatial distribution of the best reservoir quality is therefore a combination of where there is thorough dolomitization as well as where original depositional porosity and permeability is preserved. Isotopic analyses of the new core samples may help to refine the paragenesis and provide a new framework for interpretation of the 3D seismic data.
This abstract is submitted to the session in celebration of the career of Paul “Mitch” Harris. Mitch has taught me that to understand carbonates, you need to investigate all aspects of its depositional and diagenetic history by using core, well logs, seismic interpretation, biostratigraphy, geochemistry, petrography, outcrop analogs and anything else that you can. This project is my attempt to apply his teachings in order to understand the complex reservoir. Significant oil and gas discoveries in the Topkhana and Kurdamir blocks of southeast Kurdistan are primarily contained within the Oligocene Kirkuk group. This group is regionally composed of middle ramp foraminiferal and red algae grainstones as well as coral boundstones/rudstones that likely form small bioherms. Reservoir quality is highly dependent on both the original depositional facies as well as the overprint of dolomitization. Predicting the spatial distribution of the best reservoir quality is challenging. Earlier studies (Hsieh et al., 2013) suggest that the best reservoir rock quality occurs where there is intense dolomitization along with dissolution of the foraminiferal tests. Original intergranular porosity was often occluded by marine cement and thus, non-dolomitized grainstones were considered poorer quality and not the primary target. Based on Sr-isotope geochemistry, dolomitization was shown to occur primarily in the earliest Miocene. This suggested a “top down” dolomitization of the Kirkuk Group where the dolomite geobody would be located beneath the dolomitizing fluid body. Early interpretation of the 3D seismic data supported this hypothesis. However, recently collected cores provided not only a down-dip limit to the dolomitization front, but also added a twist in the reservoir quality story. Dolomitization only improved reservoir quality if the process was complete while partially dolomitized rocks were in fact poorer quality than non-dolomitized rocks. Additionally, coral boundstone and rudstones that seem to preserve the depositional porosity have similar flow properties as the best dolomitized rock. The spatial distribution of the best reservoir quality is therefore a combination of where there is thorough dolomitization as well as where original depositional porosity and permeability is preserved. Isotopic analyses of the new core samples may help to refine the paragenesis and provide a new framework for interpretation of the 3D seismic data.
Panel_14765
Panel_14765
4:25 PM
4:45 PM
4:45 p.m.
Carbonate Eolianites in the Exumas — The Legacy of Vanishing Ebb Tidal Deltas During a Sea Level Rise
Four Seasons Ballroom 1
By P. Harris, K. L. Jackson, M. Petrie, G. P. Eberli
The high-energy platform margin in the Exumas Islands portion of Great Bahama Bank is dominated by a tidal delta depositional motif, typified by islands (Pleistocene or Holocene) bounding open circulating tidal channels within which vigorous tidal flow leads to the formation of flood and ebb tidal lobes formed of ooid and other types of carbonate sands. As shown by the robust example of this motif associated with the tidal channel between Shroud and Hawksbill Cays, significant amounts of sediment form fully aggraded flood and ebb lobes and adjacent sand flats, and are reworked from the ebb tidal lobe by longshore currents and storms to nourish adjacent beaches and form back-beach sand ridges that quickly become cemented by meteoric cements. Isolated Early Holocene (~5,000 years old) eolianites on several islands in the Exumas, e.g. Gaulin Cay, Bitter Guana Cay, Cambridge Cay, O’Brien’s Cay, and Warderick Wells Cay, are problematic, in that these significant relict deposits of ooid and peloid sands with large-scale foreset bedding clearly indicating sediment transport onto the platform are challenging to explain from the standpoint of the source of the carbonate sand. Age-related, coeval facies are lacking, and laterally adjacent shorelines generally lack appreciable Holocene sediment and commonly show signs of erosion and coastline retreat. We propose these eolianites are the result of ebb tidal lobe cannibalization by longshore currents and storms, and their apparent non-equilibrium state with the modern seaward coastline strongly suggests a major change in depositional conditions between time of deposition of the eolianites and present-day. It is likely that tidal delta lobe development occurred in these areas a few thousand years ago during a lower position of sea level when more vigorous tidal currents were concentrated in channels formed in deeper Pleistocene lows. Present sea level has resulted in less vigorous tidal currents in these areas and cannibalization through erosion (longshore currents and storms) of the ebb tidal delta lobe, beach sands, and the seaward portions of the eolianites themselves. The resultant, significant eolianite deposits at these localities are difficult to understand in the absence of their associated early Holocene facies belts, and would pose a very challenging dilemma to explain them in any ancient scenario. Associated facies are missing entirely or are severely truncated.
The high-energy platform margin in the Exumas Islands portion of Great Bahama Bank is dominated by a tidal delta depositional motif, typified by islands (Pleistocene or Holocene) bounding open circulating tidal channels within which vigorous tidal flow leads to the formation of flood and ebb tidal lobes formed of ooid and other types of carbonate sands. As shown by the robust example of this motif associated with the tidal channel between Shroud and Hawksbill Cays, significant amounts of sediment form fully aggraded flood and ebb lobes and adjacent sand flats, and are reworked from the ebb tidal lobe by longshore currents and storms to nourish adjacent beaches and form back-beach sand ridges that quickly become cemented by meteoric cements. Isolated Early Holocene (~5,000 years old) eolianites on several islands in the Exumas, e.g. Gaulin Cay, Bitter Guana Cay, Cambridge Cay, O’Brien’s Cay, and Warderick Wells Cay, are problematic, in that these significant relict deposits of ooid and peloid sands with large-scale foreset bedding clearly indicating sediment transport onto the platform are challenging to explain from the standpoint of the source of the carbonate sand. Age-related, coeval facies are lacking, and laterally adjacent shorelines generally lack appreciable Holocene sediment and commonly show signs of erosion and coastline retreat. We propose these eolianites are the result of ebb tidal lobe cannibalization by longshore currents and storms, and their apparent non-equilibrium state with the modern seaward coastline strongly suggests a major change in depositional conditions between time of deposition of the eolianites and present-day. It is likely that tidal delta lobe development occurred in these areas a few thousand years ago during a lower position of sea level when more vigorous tidal currents were concentrated in channels formed in deeper Pleistocene lows. Present sea level has resulted in less vigorous tidal currents in these areas and cannibalization through erosion (longshore currents and storms) of the ebb tidal delta lobe, beach sands, and the seaward portions of the eolianites themselves. The resultant, significant eolianite deposits at these localities are difficult to understand in the absence of their associated early Holocene facies belts, and would pose a very challenging dilemma to explain them in any ancient scenario. Associated facies are missing entirely or are severely truncated.
Panel_14762
Panel_14762
4:45 PM
5:05 PM