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Offshore Angola has to date delivered recoverable reserves in excess of 20 billion barrels of oil equivalent. This has been encountered in two distinct play systems: the Upper Cretaceous Pinda carbonates sourced by Lower Creatceous lacustrine mudstones and Tertiary deepwater slope turbidite sands sourced by underlying Upper Cretaceous marine mudstones. An extension of the Girassol play into Block 18 to the south will be used to describe how high quality 3D seismic data coupled with a detailed analysis of rock properties led to an unprecedented 6 successes out of 6 wells in the block, including the giant Plutonio discovery. Industry is turning once more to the carbonate play potential - this time in deepwater. It would seem that the Angola offshore success story is set to continue for some time to come.

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Desktop /Portals/0/images/_site/AAPG-newlogo-vertical-morepadding.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Oil Exploration Offshore Angola: Past, Present & Future
We describe the structure, microstructure, and petrophysical properties of fault rocks from two normal fault zones formed in low-porosity turbiditic arkosic sandstones, in deep diagenesis conditions similar to those of deeply buried reservoirs. These fault rocks are characterized by a foliated fabric and quartz-calcite sealed veins, which formation resulted from the combination of the (1) pressure solution of quartz, (2) intense fracturing sealed by quartz and calcite cements, and (3) neoformation of synkinematic white micas derived from the alteration of feldspars and chlorite. Fluid inclusion microthermometry in quartz and calcite cements demonstrates fault activity at temperatures of 195degC to 268degC. Permeability measurements on plugs oriented parallel with the principal axes of the finite strain ellipsoid show that the Y axis (parallel with the foliation and veins) is the direction of highest permeability in the foliated sandstone (10–2 md for Y against 10–3 md for X, Z, and the protolith, measured at a confining pressure of 20 bars). Microstructural observations document the localization of the preferential fluid path between the phyllosilicate particles forming the foliation. Hence, the direction of highest permeability in these fault rocks would be parallel with the fault and subhorizontal, that is, perpendicular to the slickenlines representing the local slip direction on the fault surface. We suggest that a similar relationship between kinematic markers and fault rock permeability anisotropy may be found in other fault zone types (reverse or strike-slip) affecting feldspar-rich lithologies in deep diagenesis conditions.
Show more American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/Bulletin-hero-2013-07jul.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Influence of fault rock foliation on fault zone permeability: The case of deeply buried arkosic sandstones (Gres d'Annot, southeastern France)
The shrinkage or swelling of coal as a result of gas desorption or adsorption is a well-accepted phenomenon. Its impact on permeability changes has also been recognized for two decades. Its importance has increased significantly because of the potential of coals that are not likely to be mined and depleted or nearly depleted coalbed methane reservoirs to serve as CO2 repositories. This article proposes a new theoretical technique to model the volumetric changes in the coal matrix during gas desorption or adsorption using the elastic properties, sorption parameters, and physical properties of coal. The proposed model is based on the theory of changes in surface energy as a result of sorption. The results show that the proposed model is in excellent agreement with the laboratory volumetric strain data presented in the literature during the last 50 yr. Furthermore, the proposed model can be extended to describe mixed-gas sorption behavior, which can be applied to enhanced coalbed methane and CO2 sequestration operations.
Show more American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/a-new-theoretical-approach-to-model-sorption.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true A new theoretical approach to model sorption-induced coal shrinkage or swelling
We study the effects of planform dome shape on fault patterns developing with and without concurrent regional extension oriented oblique to the long axis of the dome. The motivation was the need to understand fault and fracture patterns in two adjacent mature hydrocarbon fields in the Middle East: one, an elliptical dome, and one, an irregularly shaped dome. The largest faults have throws of approximately 30 m (sim98 ft), which is close to the resolution limit of older two-dimensional seismic reflection data. The known fault trends are not parallel to the highest transmissivity direction but could form compartment boundaries. Fault and fracture patterns developed over the modeled domes provide insight into the populations of faults and fractures that are likely to exist in the reservoirs but have been undetected because they are at or below the resolution limit of reflection seismic data. Major domal structural elements, crestal fault systems, end splay systems, and radial faults are observed in modeled domes rising both with and without concurrent regional extension. Experimental results indicate that fault and fracture patterns are influenced by the effects of dome shape, regional extension, and relative timing of uplift with respect to regional extension. The expression of particular sets of faults and fractures associated with concurrent doming and regional extension depends on the interaction among regional extension, outer arc extension over the dome, and tangential extension around the dome margins. Our results also indicate that the two adjacent natural domes possibly experienced different kinematic histories from those previously interpreted.
Show more American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/analog-modeling-of-normal-faulting-above.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Analog modeling of normal faulting above Middle East domes during regional extension
Transfer zones in rift basins are classified into convergent, divergent, and synthetic, based on the relative dip directions of adjacent faults within the transfer zone. Experimental models were constructed to determine the geometry, evolution, and fault patterns associated with each of these transfer zones. In addition, basement faults with initially approaching, laterally offset, and overlapping geometries were modeled. The models consisted of two layers, with stiff clay representing basement and soft clay representing the sedimentary cover. Laser scanning and three-dimensional surface modeling were used to determine the map geometry to compare the models with examples of natural structures. The experimental models showed many similarities with conceptual models but also showed more details and a few significant differences. Typically, divergent transfer zones are narrower than convergent transfer zones, for the same initial spacing between basement faults. The differences between the different initial fault configurations (approaching, laterally offset, or overlapping) are the degree of interaction of the secondary faults, the amount of overlap between the fault zones, and in some cases, the width of the transfer zone. The main faults propagate laterally and upward and curve in the direction of dip of the faults, so that the faults curve toward each other in convergent transfer zones, away from each other in divergent transfer zones, and in the same direction in synthetic transfer zones. A primary difference with schematic models is the significant component of extensional fault propagation folding (drape folding), accompanied by secondary faulting within the sedimentary cover, especially in the early stages of fault propagation. Therefore, all three types of transfer zones are characterized by significant folding and related variations in the shapes of structures. The transfer zones are marked by a progressive change in relief from the footwall to the hanging wall, resulting in a saddle-shaped geometry. The hanging walls of the faults are marked by a gentle flexure or rollover into the fault, with the amount of flexure increasing with fault throw away from the fault tip. The geometries and fault patterns of the experimental structures match some of the observations in natural structures and also provide predictive analogs for interpretation of surface and subsurface structures and the delineation of structural traps in rift basins.
Show more American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/Experimental-models-of-transfer-zones-in-rift.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Experimental models of transfer zones in rift systems
The geometries of clay smears produced in a series of direct shear experiments on composite blocks containing a clay-rich seal layer sandwiched between sandstone reservoir layers have been analyzed in detail. The geometries of the evolving shear zones and volume clay distributions are related back to the monitored hydraulic response, the deformation conditions, and the clay content and strength of the seal rock. The laboratory experiments were conducted under 4 to 24 MPa (580–3481 psi) fault normal effective stress, equivalent to burial depths spanning from less than approximately 0.8 to 4.2 km (0.5 to 2.6 mi) in a sedimentary basin. The sheared blocks were imaged using medical-type x-ray computed tomography (CT) imaging validated with optical photography of sawn blocks. The interpretation of CT scans was used to construct digital geomodels of clay smears and surrounding volumes from which quantitative information was obtained. The distribution patterns and thickness variations of the clay smears were found to vary considerably according to the level of stress applied during shear and to the brittleness of the seal layer. The stiffest seal layers with the lowest clay percentage formed the most segmented clay smears. Segmentation does not necessarily indicate that the fault seal was breached because wear products may maintain the seal between the individual smear segments as they form. In experiments with the seal layer formed of softer clays, a more uniform smear thickness is observed, but the average thickness of the clay smear tends to be lower than in stiffer clays. Fault drag and tapering of the seal layer are limited to a region close to the fault cutoffs. Therefore, the comparative decrease of sealing potential away from the cutoff zones differs from predictions of clay smear potential type models. Instead of showing a power-law decrease away from the cutoffs toward the midpoint of the shear zone, the clay smear thickness is either uniform, segmented, or undulating, reflecting the accumulated effects of kinematic processes other than drag. Increased normal stress improved fault sealing in the experiments mainly by increasing fault zone thickness, which led to more clay involvement in the fault zone per unit of source layer thickness. The average clay fraction of the fault zone conforms to the prediction of the shale gouge ratio (SGR) model because clay volume is essentially preserved during the deformation process. However, the hydraulic seal performance does not correlate to the clay fraction or SGR but does increase as the net clay volume in the fault zone increases. We introduce a scaled form of SGR called SSGR to account for increased clay involvement in the fault zone caused by higher stress and variable obliquity of the seal layer to the fault zone. The scaled SGR gives an improved correlation to seal performance in our samples compared to the other algorithms.
Show more American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/Three-dimensional-structure-of-experimentally-produced.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Three-dimensional structure of experimentally produced clay smears: Implications for fault seal analysis
We use samples from undeformed and deformed sandstones (single deformation band, deformation band cluster, slip-surface cataclasite, and fault core slip zone) to characterize their petrophysical properties (porosity, permeability, and capillary pressure). Relationships between permeability and porosity are described by power-law regressions where the power-law exponent (D) decreases with the increasing degree of deformation (strain) experienced by the sample from host rock (D, sim9) to fault core (D, sim5). The approaches introduced in this work will allow geologists to use permeability and/or porosity measurements to estimate the capillary pressures and sealing capacity of different fault-related rocks without requiring direct laboratory measurements of capillary pressure. Results show that fault core slip zones have the highest theoretical sealing capacity (gt140-m [459-ft] oil column in extreme cases), although our calculations suggest that deformation bands can locally act as efficiently as fault core slip zones in sealing nonwetting fluids (in this study, oil and CO2). Higher interfacial tension between brine and CO2 (because of the sensitivity of CO2 to temperature and pressure) results in higher capillary pressure and sealing capacity in a brine and CO2 system than a brine and oil system for the same samples.
Show more American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/insight-into-petrophysical-properties.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Insight into petrophysical properties of deformed sandstone reservoirs
Emission of carbon dioxide (CO2) from fossil-fueled power generation stations contributes to global climate change. Capture of CO2 from such stationary sources and storage within the pores of geologic strata (geologic carbon storage) is one approach to mitigating anthropogenic climate change. The large storage volume needed for this approach to be effective requires injection into pore space saturated with saline water in reservoir strata overlain by cap rocks. One of the main concerns regarding storage in such rocks is leakage via faults. Such leakage requires, first, that the CO2 plume encounter a fault and, second, that the properties of the fault allow CO2 to flow upward. Considering only the first step of encounter, fault population statistics suggest an approach to calculate the probability of a plume encountering a fault, particularly in the early site-selection stage when site-specific characterization data may be lacking. The resulting fault encounter probability approach is applied to a case study in the southern part of the San Joaquin Basin, California. The CO2 plume from a previously planned injection was calculated to have a 4.1% chance of encountering a fully seal offsetting fault and a 9% chance of encountering a fault with a throw half the seal thickness. Subsequently available information indicated the presence of a half-seal offsetting fault at a location 2.8 km (1.7 mi) northeast of the injection site. The encounter probability for a plume large enough to encounter a fault with this throw at this distance from the injection site is 25%, providing a single before and after test of the encounter probability estimation method.
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Desktop /Portals/0/PackFlashItemImages/WebReady/measuring-and-modeling-fault-density.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Measuring and modeling fault density for CO2 storage plume-fault encounter probability estimation
Volumetric restoration can provide crucial insights into the structural evolution of three-dimensional (3-D) petroleum systems. A major limitation to its widespread application is the need to include complex architectures and realistic mechanics such as flexural slip. We apply an implicit approach that allows for, including unconformities, thin and/or pinched-out layers in the models but that cannot explicitly localize slip along horizons. To take advantage of this approach while accounting for flexural slip in 3-D restoration, we investigate new geomechanical properties. We consider flexural slip folding as a result of stacked rigid and thin weak layers, which can be modeled using transversely isotropic properties. We compare restorations of an anticline using transversely isotropic properties, isotropic properties, and a stack of rigid isotropic layers with nonfrictional slip between the layers. Our results show that transversely isotropic properties reasonably approximate flexural slip folding. We use these new tools to model the evolution of a complex system located in the Niger Delta toe. The system includes a detachment fold, a fault-bend fold, and a structural wedge formed in series. Growth stratigraphy and erosional surfaces delimit the kinematics of deformation. Regional erosive surfaces, 3-D gradients of fault slip, and vertical variations in mechanical strength motivated the use of our new restoration techniques. Restoring two growth units results not only in reinforcing the interpretation that the area is behaving as a deforming thrust sheet at critical taper, but also in highlighting coeval activity on both the hinterland structures and the toe of the thrust belt.
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Desktop /Portals/0/PackFlashItemImages/WebReady/Handling-natural-complexity-in-three-dimensional.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Handling natural complexity in three-dimensional geomechanical restoration, with application to the recent evolution of the outer fold and thrust belt, deep-water Niger Delta

Early detection: A Canadian geophysicist is finding success by incorporating existing 3-D data to determine fracture networks in the Bakken Shale.

American Association of Petroleum Geologists (AAPG)
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Online Training
21 August, 2014 21 August, 2099 10831 Desktop /Portals/0/PackFlashItemImages/WebReady/esymp-mexicos-oil-and-gas-history-new-discoveries-opportunities-and-energy-reform-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true
21 August 2014 - 21 August 2099
The goal of this e-symposium is to review the status of the Mexican upstream sector, and to provide a review of the most prolific and prospective areas in Mexico, with a focus on opportunities for international participation, given the upcoming energy reform in Mexico. 
19 August, 2010 19 August, 2010 1462 Desktop /Portals/0/PackFlashItemImages/WebReady/oc-es-challenging-the-paradigm-missing-section-normal-fault.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true
19 August 2010

This presentation will show where there are cases of missing sections, but none of them can be attributed to normal faulting.

14 February, 3000 14 February, 3000 7817 Desktop /Portals/0/PackFlashItemImages/WebReady/oc-es-generic-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true
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The following short course option was developed for geology and geophysics students that have not had much exposure to how geoscience is applied in industry. It can be tailored for undergraduate juniors and seniors or graduate students. The agenda can be modified to meet specific needs and time constraints. to discuss options.

Request a visit from Fred Schroeder!

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