Renaud Bouroullec

Quantitative outcrop characterization of an analog to weakly confined submarine channel systems: Morillo 1 member, Ainsa Basin, Spain

Weakly confined channel systems are common in low-relief minibasins on continental margins and are important hydrocarbon reservoirs. They are characterized by channels that diverge in the proximal part of the basin and converge because of topographic confinement in the distal part of the basin. The Morillo 1 member, in the Ainsa Basin, Spain, is an excellent outcrop analog of a weakly confined submarine channel system. Data from the Morillo 1 member are used to quantitatively document how reservoir characteristics vary laterally and longitudinally in weakly confined submarine channel reservoirs. The key axis-to-margin patterns are the proportions of channel elements, channel complexes, channel-complex sets, reservoir facies, and net sand content; static connectivity decreases laterally from the axis to the margins of the system. The key longitudinal patterns in the updip area are channel elements that have levees, are spatially dispersive, and have a radially divergent map pattern. In the downdip area, channel elements are spatially focused and have uniform orientations, and the proportion of channel elements does not change along the longitudinal profile. However, the size of channel elements, percentage of reservoir facies, and connectivity of channel elements are higher in the downdip area. Patterns identified herein are significant because they cannot be resolved using subsurface or sea-floor data. Results of this study can therefore be used to reduce uncertainty in the interpretation of subsurface data, provide input to constrain rule-based forward stratigraphic models, and provide input to constrain reservoir models.

The use of spectral recomposition in tailored forward seismic modeling of outcrop analogs

Spectral recomposition is an improved methodology for generating forward seismic models of outcrop analogs that make use of the full range of frequencies found within real-world seismic volumes. It overcomes the issue common to conventional forward seismic models in which single-peak frequencies are modeled, with the resultant models not capturing the range of frequency content that is found in the real world image. This variable frequency content of real-world seismic volumes has long been known to contain more detailed information within different spectral bands, which forms the basis of the spectral decomposition process, in which different spectral frequencies can correlate to different stratigraphic thicknesses, for example. In this article, we introduce and illustrate the use of a new method termed spectral recomposition. Spectral recomposition is a poststack seismic method operating in the frequency domain that recomposes forward seismic models generated at separate peak frequencies to derive a final image, which has a frequency spectrum similar to that of a targeted real-world image. Using this method, forward seismic models can be tailored to specific real-world images and be used as a more appropriate comparison between the known outcrop geometries and those that are imaged in the subsurface.

Integration of GPR with stratigraphic and lidar data to investigate behind-the-outcrop 3D geometry of a tidal channel reservoir analog, upper Ferron Sandstone, Utah

Highly compartmentalized reservoirs are commonly attributed to heterogeneous facies as well as vertical/horizontal stratigraphic trends associated with depositional cycles. Detailed information on stratigraphic heterogeneity is essential to fully exploit a reservoir. Subseismic-scale reservoir stratigraphy can be investigated in outcrop by integrating multiple high-resolution sedimentological data, lidar (light detection and ranging) data, and GPR (ground-penetrating radar) data. This combination of different data sets can help to characterize ancient tidal channels exposed in outcrops, which are considered to be heterogeneous compartmentalized sandstone reservoir analogs. This multidisciplinary approach not only attempts to describe rarely seen Cretaceous tidal-channel deposits at the Dry Wash outcrop (Figure 1) in three dimensions, but it also demonstrates how the different types of data can be integrated to better understand ancient complex shallow-marine depositional systems.

Geometry and kinematics of Neogene allochthonous salt systems in the Mississippi Canyon, Atwater Valley, western Lloyd Ridge, and western DeSoto Canyon protraction areas, northern deep-water Gulf of Mexico

The structural history of the Mississippi Canyon, Atwater Valley, westernDeSoto, and western Lloyd Ridge protraction areas in the northeastern deep-water Gulf of Mexico is of a basin influenced by complex salt tectonics that controlled the formation of intraslope minibasins and sediment distribution. Large volumes of Middle Jurassic autochthonous salt (Louann Salt) were successively mobilized upward into younger sediments, forming three distinctive allochthonous salt layers: At the top Barremian, at the top Cretaceous, and within the Neogene interval. Four types of Neogene allochthonous salt systems are identified based on the geometry of the allochthonous salt bodies and associated faults, folds, and minibasins: (1) basement-controlled, (2) counterregional, (3) roho, and (4) fold-belt-related salt systems. The allochthonous salt systems are defined based on salt-body geometry, salt-stem geometry, associated fault network, and associated stratigraphic geometries. The distribution of the Neogene allochthonous salt systems is controlled by the original autochthonous salt thickness, the basement configuration, and the regional sediment-loading pattern. The basement-controlled Neogene salt systems are present in the eastern and northern part of the study area where little basinward gravitational gliding occurred. The counterregional and roho allochthonous salt systems are associated with the basinward evacuation of salt in response to extensive sediment loading. The fold-belt-related allochthonous salt systems are present in the southern part of the salt province where extensive shortening remobilized salt into and onto contractional structures. The detailed study of those Neogene allochthonous salt systems is used to build conceptual kinematic models for each style of salt system. Copyright

Regional structural setting and evolution of the Mississippi Canyon, Atwater Valley, western Lloyd Ridge, and western DeSoto Canyon protraction areas, northern deep-water Gulf of Mexico

The structural framework and evolution from the Middle Jurassic to the present of the Mississippi Canyon, Atwater Valley, western DeSoto Canyon, and western Lloyd Ridge protraction areas consist of a complex history influenced by basement fabric, multiple stages of salt movement, and gravitational gliding. A detailed tectono-stratigraphic interpretation of the study area indicates that three main stages of salt movement controlled sediment dispersal patterns and the formation and evolution of intraslope minibasins. These three stages of salt movement occurred during the Cretaceous, the Paleogene, and the Neogene. Basement structures were the primary control on initial salt kinematics, affecting gravity-driven slope deformation and resulting in a wide variety of structural styles. Basement (acoustic basement) structures (horsts, grabens, and half grabens) formed prior to the deposition of the Middle Jurassic autochthonous Louann Salt. These features are interpreted to have controlled the original thickness of the autochthonous salt layer and subsequent salt-withdrawal patterns. Mesozoic structures, such as extensional-compressional gliding systems and expulsion rollovers, formed above the autochthonous salt. Three levels of allochthonous salt systems are identified: (1) approximate top Barremian, (2) top Cretaceous, and (3) intra-Neogene (between 10 and 4 Ma). Early emplacement of two allochthonous salt layers is present in the northeastern part of the study area, whereas the Neogene allochthonous salt system extends throughout the Mississippi Canyon, western DeSoto Canyon, and northern Atwater Valley protraction areas. Salt from the autochthonous and two deep allochthonous salt layers was expelled vertically and basinward during theNeogene, feeding the younger allochthonous salt systems. The autochthonous and deep allochthonous salt layers were detachments for many of the large Neogene extensional (growth faults and turtles) and contractional (anticlines and thrust faults) structures, whereas the Neogene allochthonous salt system accommodated suprasalt minibasins associated with counterregional and roho salt systems. These three allochthonous salt layers were successively loaded by gravity-flow sediments, resulting in deep (above autochthonous or deep allochthonous salt layers) and shallow (supra-Neogene allochthonous salt) minibasin formations and local development of extensive salt welds. Northwest-southeast-oriented strike-slip structures, active during the Neogene, are present in the salt province within the study area. They are related to basinwide heterogeneities in the salt distribution and are controlled by differential basinward movement of adjacent suprasalt minibasins. Copyright

An overview of the petroleum systems of the northern deep-water Gulf of Mexico

The northern deep-waterGulf ofMexico is one of themost active deep-water petroleum provinces in the world. This paper introduces the regional geologic setting for the northern deep-water Gulf of Mexico and briefly discusses the importance of technology in developing the areas resources. Exploration has focused on four major geologic provinces: Basins, Subsalt, Fold Belt, and Abyssal Plain. These provinces formed from the complex interactions between Mesozoic-Cenozoic sedimentation and tectonics. Improved understanding of the geology of these provinces has largely been accomplished by improvements in seismic acquisition and processing. In addition, advances in drilling technology have permitted drilling and field development in increasingly greater water depths. The 226 oil and gas fields and discoveries in the northern deep-water Gulf of Mexico are summarized in terms of their exploration and development history, producing facility, ages of reservoirs (Upper Jurassic, upper Paleocene-lower Eocene, Oligocene, lower Miocene-upper Pleistocene), and trap type (structural, combined structural-stratigraphic, and stratigraphic). In addition, the interpreted regional distribution of Upper Jurassic and possible Lower Cretaceous source, source rocks is shown, in part based on the 26wells that have penetrated these source rocks. The eight papers in this special issue review the geology of the Mississippi Canyon and northern Atwater Valley protraction areas. The first five papers review the subregional structural setting and the evolution of its tectonics and petroleumsystems. The final three papers summarize the geologic evolution of two economically important intraslope basins-ThunderHorse andMensa-in terms of their stratigraphy, structural evolution, and petroleumsystems. These two basins contain two of the larger oil and gas fields, respectively, in the northern deep-water Gulf of Mexico. Copyright

Petroleum geology of the Mississippi Canyon, Atwater Valley, western DeSoto Canyon, and western Lloyd Ridge protraction areas, northern deep-water Gulf of Mexico: Traps, reservoirs, and tectono-stratigraphic evolution

ABSTRACT The petroleum geology of the Mississippi Canyon, Atwater Valley, western DeSoto Canyon, and western Lloyd Ridge protraction areas, offshore northern Gulf of Mexico, is controlled by the interaction of salt tectonics and high sedimentation rate during the Neogene and resulted in a complex distribution of reservoirs and traps. We evaluate 87 fields and discoveries: 51 with combined structural/stratigraphic traps (three-way closures), 19 with structural traps (four-way closures), and 17 with stratigraphic traps. Three of these discoveries are in Upper Jurassic eolian reservoirs; the remaining discoveries are in Neogene deep-water reservoirs. The tectono-stratigraphic evolution of the area is analyzed at 11 discrete intervals between 24 Ma and the present. Four stratigraphic external forms—troughs, bowls, wedges, and sheets—are integrated with the structural geology to understand the changing shape of subbasins and minibasins, primarily in a slope setting. This analysis shows how the allochthonous salt systems evolved over time and how salt movement affected sedimentation patterns and subbasin evolution. The study area includes some of the largest fields in the northern deep-water Gulf of Mexico, such as the Thunder Horse field, which produces from an anticlinal (turtle) structure, or the Mars–Ursa and associated fields with greater than 1.5 billion BOE estimated ultimate recovery, which developed with a counterregional allochthonous salt system. The remaining fields have considerably smaller reserves, which are controlled by the area within closure and the number of reservoir intervals. Most of fields in the study area are contained within sheet-shaped or wedge-shaped stratigraphic external forms and have four-way or three-way trapping configurations. These findings indicate the profound effect of mobile salt on the petroleum geology of the region.

Sequence stratigraphic evolution of the Mensa and Thunder Horse intraslope basins, northern deep-water Gulf of Mexico—Lower Cretaceous through upper Miocene (8.2 Ma): A case study

Thunder Horse and Mensa are two of the largest fields of oil or gas, respectively, in the northern deep-water Gulf of Mexico. The fields are present in adjacent intraslope minibasins, located approximately 12 mi (19 km) apart in Mississippi Canyon. Both fields illustrate important complexities of deep-water sedimentation. Analysis is based on the integration of wire-line logs, biostratigraphy, and a 378-mi2 (979-km2), three-dimensional seismic data set. Thunder Horse and Mensa reservoirs were deposited during themiddle to lateMiocene.Changes in paleobathymetry controlled the reservoir deposition, initially as salt withdrawal and later as turtle structures. From 125 to 24 Ma, the lithologies in both intraslope basins are interpreted as dominantly deep-water marls with interbedded shales. From 24 to 14.35 Ma, major input of deep-water siliciclastic sediments began. Sands were deposited in amalgamated sheets and amalgamated channel-fill units within the two major paleobathymetric lows; by contrast, shales were deposited across paleobathymetric highs. Between 14.35 and 13.05 Ma, the Thunder Horse turtle formed, creating a paleobathymetric high. Channelized sands were diverted around and deposited on the flanks of the structure. Meanwhile, to the north at Mensa, thick channelfill sediments continued to be deposited. From 12.2 to 8.2 Ma, the lithologies throughout the entire area are dominantly overbank shales with thin channel-fill sands, suggesting that large volumes of sand bypassed the study area farther downslope to the south. Finally, at 9.0 Ma, Mensas sheet-sand reservoir represents a different setting; sands were deposited near the crest of the Mensa turtle, which had subtle bathymetric expression. Copyright

Structural setting and evolution of the Mensa and Thunder Horse intraslope basins, northern deep-water Gulf of Mexico: A case study

The Mensa and Thunder Horse intraslope minibasins in southcentralMississippi Canyon, northern deep-water Gulf ofMexico, had a linked structural evolution from the Early Cretaceous through the late Miocene. Analysis of the two minibasins illustrates the complexities of deep-water sedimentation and salt tectonics in intraslope minibasins. This study is based on the integration of a 378-mi2 (979-km2) three-dimensional seismic data set,wire-line logs, and biostratigraphic data. These two minibasins comprise several structural features that affected their geologic evolution: basement faults, autochthonous salt, three allochthonous salt systems (top Barremian, top Cretaceous, and Neogene), a growth fault and raft system, three major turtle structures with associated extensive crestal faults, and strike-slip faults. Remnant allochthonous salt pillows are present above the 125 Ma horizon (approximate top Barremian system) and on the 66 Ma horizon (top Cretaceous system) throughout the Mensa minibasin, whereas the top Cretaceous allochthonous salt system is identified regionally by a salt weld in the Thunder Horse area. These allochthonous salt systems formed weld surfaces beneath the Mensa and Thunder Horse turtle structures. Structural features and associated minibasins evolved during several discrete intervals. From the Early Cretaceous through the latest Oligocene (125 to 24 Ma), an extensive allochthonous salt canopy was present within the Mensa and Thunder Horse minibasins. During this interval, sediments loaded the salt, forming thinwedge-and sheet-formdeposits in theMensa area and a thick, northwest-Trending trough in the ThunderHorse area. A secondary allochthonous salt system extruded at the Top Cretaceous level, as seen by remnant salt bodies. Salt withdrawal from these allochthonous salt systems provided accommodation for bowl-and trough-shaped external stratigraphic forms to develop during the Miocene. High sedimentation rates produced salt evacuation from these allochthonous salt systems and initiated diapirism that formed the Neogene allochthonous salt level. The prominent turtle structures in the two minibasins, critical to the formation of traps to the two major fields, developed at slightly different times: Thunder Horse at 14.35 and Mensa at 11.4 Ma. Copyright

Three-dimensional petroleum systems modeling of the Mensa and Thunder Horse intraslope basins, northern deep-water Gulf of Mexico: A case study

The petroleum systems of two adjacent Miocene intraslope minibasins in the northern deep-water Gulf of Mexico are modeled to investigate why one of them produces primarily gas but the other produces oil. Specifically, the Mensa field produces gas from a faulted four-way closure that overlies a turtle structure, whereas the adjacent Thunder Horse field produces from a turtle structure with four-way structural closure. To resolve this issue, a three-dimensional petroleum-system model was constructed, whose results indicate that the Lower Cretaceous source interval, comprising type II kerogen, matured significantly earlier in the Mensa basin; the oil window was reached between 11.4 and 9.0 Ma, and the thermogenic gaswindowwas reached between 6.2 and 0.0Ma. By contrast, within the Thunder Horse basin, the source interval reached the oil window by 10.75 to 9.4Ma and largely remains in the oilwindow. TheThunderHorse trap had formed by 13.05Ma, which was before the end of the oil window. The Mensa trap (9.0-8.2Ma) was not in placewhen the source rock passed though the oil window. The primary control on the timing ofmaturation and charge is related to the original thickness of allochthonous salt that created the accommodation for the thick Miocene deep-water sediments. Originally, the Mensa minibasin contained thicker Cretaceous allochthonous salt than the Thunder Horse minibasin. Consequently, as the salt was loaded with sediment and completely evacuated, the turtle structure (trap) formed earlierin Thunder Horse field than in Mensa. By contrast, the source rocks matured earlier in Mensa, prior to the deposition of reservoir sands and the formation of the trap. The results indicate that turtle structures with similar appearances can have subtle differences in the timing of their petroleum systems, which ultimately control whether the feature is charged and with what fluid. These features must be modeled carefully in evaluating their exploration potential. Copyright