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Structural Analysis - Other

29 Apr

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Bulletin Article

Geometry, kinematics, and displacement characteristics of tear-fault systems: An example from the deep-water Niger Delta

We use three-dimensional seismic reflection data and new map-based structural restoration methods to define the displacement history and characteristics of a series of tear faults in the deep-water Niger Delta. Deformation in the deep-water Niger Delta is focused mostly within two fold-and-thrust belts that accommodate downdip shortening produced by updip extension on the continental shelf. This shortening is accommodated by a series of thrust sheets that are locally cut by strike-slip faults. Through seismic mapping and interpretation, we resolve these strike-slip faults to be tear faults that share a common detachment level with the thrust faults. Acting in conjunction, these structures have accommodated a north –south gradient in westward-directed shortening. We apply a map-based restoration technique implemented in Gocad to restore an upper stratigraphic horizon of the late Oligocene and use this analysis to calculate slip profiles along the strike-slip faults. The slip magnitudes and directions change abruptly along the lengths of the tear faults as they interact with numerous thrust sheets. The discontinuous nature of these slip profiles reflects the manner in which they have accommodated differential movement between the footwall and hanging-wall blocks of the thrust sheets. In cases for which the relationship between a strike-slip fault and multiple thrust faults is unclear, the recognition of this type of slip profile may distinguish thin-skinned tear faults from more conventional deep-seated, throughgoing strike-slip faults.

Added on 28 February, 2014

Bulletin Article

Influence of fault rock foliation on fault zone permeability: The case of deeply buried arkosic sandstones (Gres d'Annot, southeastern France)

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 195C to 268C. 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.

Added on 30 June, 2013

Bulletin Geologic Note

A new theoretical approach to model sorption-induced coal shrinkage or swelling

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.

Added on 30 June, 2013

Bulletin GeoHorizon

Analog modeling of normal faulting above Middle East domes during regional extension

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 (98 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.

Added on 31 May, 2013

Bulletin Article

Experimental models of transfer zones in rift systems

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.

Added on 30 April, 2013

Bulletin Article

Three-dimensional structure of experimentally produced clay smears: Implications for fault seal analysis

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.

Added on 30 April, 2013

Bulletin Article

Insight into petrophysical properties of deformed sandstone reservoirs

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, 9) to fault core (D, 5). 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 (140-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.

Added on 31 March, 2013

Bulletin Article

Measuring and modeling fault density for CO2 storage plume-fault encounter probability estimation

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.

Added on 31 March, 2013

Bulletin Article

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

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.

Added on 31 December, 2012

Explorer Emphasis Article By Diane Freeman

Integrated Data Helps Spot High EUR Wells

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

Added on 01 June, 2012

Webinar By Kevin Hill,Peter Grant

Virtual Webinar

Thursday, 2 July 2020, 4:00 p.m.–5:00 p.m.

The Bight Basin, South Australia, One of the World's Largest Unexplored Deltas. Evolution and Prospectivity; Seismic, Structure, and Balanced Sections

Presented by Kevin C. Hill, Associate Professor, University of Melbourne Gravity modelling of Australia's southern margin reveals that the initial rift with Antarctica was beneath the current Ceduna Delta. A regional, high-quality seismic traverse from the coast to oceanic crust across the Bight Basin has been assembled and interpreted in detail, then balanced, restored, decompacted, and replaced at paleo-water depths. The Late Cretaceous Ceduna Delta developed above a Late Jurassic-Early Cretaceous rift basin in three stages punctuated by significant pulses of uplift and erosion across areas >100 km wide and with up to 1 km of erosion. The Cenomanian White Pointer delta prograded into deepening water and hence underwent gravitational collapse. This was terminated in the Santonian when the Antarctic margin was pulled out from below, thus supplying heat to a remnant thicker outer margin crust, causing doming and erosion. Importantly, this established the saucer-shaped geometry of the Ceduna Delta that persisted throughout its development, so that any hydrocarbons generated in the southern half of the basin would have migrated towards this outer margin high. The Tiger Formation was deposited in shallow water in a full rift basin prior to breakup, which was followed by regional thermal subsidence. The Hammerhead delta developed on the newly formed passive margin but was terminated by another pulse of uplift and erosion, perhaps associated with a change in plate motion at the end of the Cretaceous. The finite element modelling of this proposed tectonic evolution will test its validity and predict hydrocarbon generation and migration through time.

Added on 02 July, 2020

Online e-Symposium

Tuesday, 9 September 2014, 2:00 p.m.–3:00 p.m.

Fluid Migration and Accumulation within the Mississippian: Why 2% Oil Cut Here, 15% One Mile Away?

Water cut is a big factor in gauging the success of horizontal drilling in the Mississippi Lime Play (MLP). The contributing factors are related in part to the spectrum of producing lithofacies and reservoir quality encountered that varies laterally and vertically, sometimes dramatically.

Added on 20 June, 2014

Online e-Symposium

Thursday, 4 October 2012, 12:00 a.m.–12:00 a.m.

Microseismic Imaging of Hydraulic Fractures: Snap, Crackle and Pops of Shale Reservoirs

Effective hydraulic fracture stimulation is critical for shale development, and microseismic is the only technology able to map the growth of these hydraulic fracture networks.

Added on 11 December, 2013

Online e-Symposium

Thursday, 17 March 2011, 12:00 a.m.–12:00 a.m.

Basic Tools for Shale Exploration

This e-symposium will provide information on which tools, processes, and procedures all geoscientists, engineers, and technical professionals working in shale plays need to understand and implement.

Added on 02 December, 2013

Online e-Symposium

Thursday, 3 June 2010, 12:00 a.m.–12:00 a.m.

Marcellus & Utica in the Field: Northern Appalachian Basin

Upon successful completion of this course, you will be able to describe faults and fractures in carbonates, black shales, and coarser clastics as they occur in the northern Appalachian Basin.

Added on 02 December, 2013

Online e-Symposium

Thursday, 16 February 2012, 12:00 a.m.–12:00 a.m.

Seismically Driven Characterization of Unconventional Shale Plays

This presentation describes a proven workflow that uses a standard narrow azimuth 3D seismic, conventional logs, image logs and core data to build five key reservoir properties required for an optimal development of shale plays.

Added on 11 December, 2013

Online e-Symposium

Friday, 20 January 2012, 12:00 a.m.–12:00 a.m.

Eagle Ford Shale Prospecting with 3D Seismic Data within a Tectonic and Depositional System Framework

The Eagle Ford Shale in South Texas is one of the more exciting shale plays in the United States at the current time.

Added on 11 December, 2013

Online e-Symposium

Thursday, 19 August 2010, 12:00 a.m.–12:00 a.m.

Challenging the Paradigm 'Missing Section = Normal Fault' and Implications for Hydrocarbon Exploration

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

Added on 02 December, 2013

Webinar By Susan Morrice

Virtual Webinar

Tuesday, 9 June 2020, 4:00 p.m.–5:00 p.m.

Bringing your own Energy to the Energy Business: First Discovery of Oil in Belize is the empowerment of the people of Belize

Visiting Geoscientist Susan Morrice shares her personal experience and insight in this talk about opportunities for geoscientists. “Geoscientists have advantages ... They are Time Travellers and have open minds. Bringing this creativity and innovation to your company or starting your own! Challenging times bring silver linings!”

Added on 28 May, 2020

Online e-Symposium

Thursday, 8 December 2011, 12:00 a.m.–12:00 a.m.

Connectivity in Fluvial Systems

This e-symposium focuses on methods for predicting connectivity within clastic fluvial systems.

Added on 11 December, 2013

DL Abstract By John Suppe

Probing What Makes the Crust Strong (or Weak): Insight from Boreholes, Earthquakes, Active Fault Systems, and Toy Models

For well over a century there have been conflicting indications of the strength of the crust and of faults and what controls them. Much of our ignorance comes quite naturally from the general inaccessibility of the crust to measurement--in contrast with our understanding of the atmosphere, which is much more accessible to observation as well as more rapidly changing. Crustal strength is best understood in deforming sedimentary basins where the petroleum industry has made great contributions, particularly in deforming petroleum basins because of the practical need to predict. In this talk we take a broad look at key issues in crustal strength and deformation and what we can learn from boreholes, earthquakes, active fault systems, and toy models.

Request a visit from John Suppe!

Added on 14 September, 2023

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