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Structural Analysis - Other

29 Apr

2nd Edition: Geological Process-Based Forward Modeling AAPG Call For Abstracts Expires in 3 days

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Explorer Geophysical Corner By Evan Staples,Kurt Marfurt,Satinder Chopra,Ze’ev Reches

Quantitative Curvature Analysis: A Case Study

Last month in this space we analyzed the relations of fracture patterns and layer curvature in clay models. This month we examine these relations in a central Oklahoma field developed by Pathfinder Exploration, Norman, Okla.

Added on 01 August, 2013

Explorer Emphasis Article By Diane Freeman

Changing North Africa

After decades spent visiting Morocco and neighboring Algeria, an AAPG member who's led countless field trips to some of the earth's most exotic places says the two old countries are evolving into modern times.

Added on 01 August, 2013

Bulletin Article

Mechanisms of shale gas storage: Implications for shale gas exploration in China

This article reviews the mechanisms of shale gas storage and discusses the major risks or uncertainties for shale gas exploration in China. At a given temperature and pressure, the gas sorption capacities of organic-rich shales are primarily controlled by the organic matter richness but may be significantly influenced by the type and maturity of the organic matter, mineral composition (especially clay content), moisture content, pore volume and structure, resulting in different ratios of gas sorption capacity (GSC) to total organic carbon content for different shales. In laboratory experiments, the GSC of organic-rich shales increases with increasing pressure and decreases with increasing temperature. Under geologic conditions (assuming hydrostatic pressure gradient and constant thermal gradient), the GSC increases initially with depth due to the predominating effect of pressure, passes through a maximum, and then decreases because of the influence of increasing temperature at greater depth. This pattern of variation is quite similar to that observed for coals and is of great significance for understanding the changes in GSC of organic-rich shales over geologic time as a function of burial history. At an elevated temperature and pressure and with the presence of moisture, the gas sorption capacities of organic-rich shales are quite low. As a result, adsorption alone cannot protect sufficient gas for high-maturity organic-rich shales to be commercial gas reservoirs. Two models are proposed to predict the variation of GSC and total gas content over geologic time as a function of burial history. High contents of free gas in organic-rich shales can be preserved in relatively closed systems. Loss of free gas during postgeneration uplift and erosion may result in undersaturation (the total gas contents lower than the sorption capacity) and is the major risk for gas exploration in marine organic-rich shales in China.

Added on 31 July, 2013

Bulletin Article

Building a three-dimensional near-surface geologic and petrophysical model based on borehole data: A case study from Chemery, Paris Basin, France

The fact that velocity models based on seismic reflection surveys commonly do not consider the near-surface geology necessitates filling the gap between the top of a velocity model and the surface of the Earth. In this study, we present a new workflow to build a shallow geologic model based exclusively on borehole data and corroborated by laboratory measurements. The study area is in Chemery (France), located at the southwestern border of the Paris Basin, where a large amount of borehole data is publicly available. The workflow starts with identifying lithologic interfaces in the boreholes and interpolating them between the boreholes. The three-dimensional (3-D) geometry of the lithologies then allows interpretation of the position, orientation, and offset of fault planes. Given the importance of the fault interpretation in the modeling process, a combination of different approaches is used to obtain the most reasonable structural framework. After creating a 3-D grid, the resulting 3-D structural model is populated with upscaled velocity logs from the boreholes, yielding the final near-surface P-wave velocity model. To better constrain the velocity model, we conducted laboratory measurements of P- and S-wave velocities in dry and water-saturated conditions on all lithologies in the model. The laboratory data were used to populate the 3-D near-surface model with VP/VS ratio values. The presented workflow accounts for one-dimensional borehole data and is much more iterative and time-consuming than workflows based on two-dimensional seismic sections. Nevertheless, the workflow results in a robust 3-D near-surface model allowing for structural interpretations and revealing the 3-D seismic velocity field.

Added on 31 July, 2013

Bulletin Article

Geothermal convection in South Atlantic subsalt lacustrine carbonates: Developing diagenesis and reservoir quality predictive concepts with reactive transport models

Prolific hydrocarbon discoveries in the subsalt, commonly known as the “presalt,” section of Brazil and the conjugate African margin have created a business imperative to predict reservoir quality in lacustrine carbonates. Geothermal convection is a style of groundwater flow known to occur in rift settings, which is capable of diagenetic modification of reservoir quality. We simulated variable density groundwater flow coupled with chemical reactions to evaluate the potential for diagenesis driven by convection in subsalt carbonates. Rates of calcite diagenesis are critically controlled by temperature gradient and fluid flux following the principles of retrograde solubility. Simulations predict that convection could operate in rift carbonates prior to salt deposition, but with rates of dissolution in the reservoir interval only on the order of 0.01 vol. %/m.y., which is too low to significantly modify reservoir quality. The exception is around permeable fault zones and/or unconformities where flow is focused and dissolution rates are amplified to 1 to 10 vol. %/m.y. and could locally modify reservoir quality. After salt deposition, simulations also predict convection with a critical function for salt rugosity. The greatest potential for dissolution at rates of 0.1 to 1 vol. %/m.y. occurs where salt welds, overlying permeable carbonates thin to 500 m (1640 ft) or less. With tens of million years residence times feasible, convection under these conditions could locally result in reservoir sweet spots with porosity modification of 1% to 10% and potentially an order of magnitude or more in reservoir permeability. Integrating quantitative model–derived predictive diagenetic concepts with traditional subsurface data sets refines exploration to production scale risking of carbonate reservoir presence and quality.

Added on 31 July, 2013

Bulletin E-P Note

Seismic geomorphological analysis and hydrocarbon potential of the Lower Cretaceous Cromer Knoll Group, Heidrun field, Norway

The Heidrun field, located on the Halten Terrace of the mid-Norwegian continental shelf, was one of the first giant oil fields found in the Norwegian Sea. Traditional reservoir intervals in the Heidrun field lie within the Jurassic synrift sequence. Most Norwegian continental shelf fields have been producing from these Jurassic reservoirs for the past 30 yr. Production has since declined in these mature fields, but recently, exploration for new reservoirs has resurged in this region. The Jurassic rifted fault blocks form a narrow continental shelf in Norway, thereby greatly reducing the areal extent for exploration and development within existing fields. As the rift axis is approached farther offshore, these Jurassic reservoirs become very deep, too risky to drill, and uneconomical. This risk has prompted exploration in more recent years of the shallower Cretaceous, postrift stratigraphic succession. Cretaceous turbidites have been found in the Norwegian and North Seas, and the discovery of the Agat field in the Norwegian North Sea confirms the existence of a working petroleum system capable of charging Cretaceous reservoirs. These Cretaceous reservoirs were deposited as slope- and basin-floor fans within a series of underfilled rifted deeps along the Norwegian continental shelf and are thought to be sourced from the localized erosion of Jurassic rifted highs. We use three-dimensional seismic and well data to document the geomorphology of a deep-water, Lower Cretaceous wedge (Cromer Knoll Group) within the hanging wall of a rift-related half graben formed on the Halten Terrace offshore mid-Norway. Seismic attribute extractions taken within this Lower Cretaceous wedge reveal the presence of several lobate to elongated bodies that seem to cascade over fault-bounded terraces associated with rifted structures. These high-amplitude, elongated bodies are interpreted as deep-water sedimentary conduits that are time equivalent to the Cretaceous basin-floor fans in more distal parts of the basin to the west. These half-graben fills have the potential to contain high-quality Cretaceous sandstones that might represent a potential new reservoir interval within the Heidrun field.

Added on 31 July, 2013

Explorer Historical Highlights By James Pindell

Origin of the Caribbean? Look Toward the Pacific

Were there enough arguments to champion a firm stand for a Pacific origin of the Caribbean lithosphere, as Kevin Burke, Bruce Malfait and others had suggested?

Added on 01 July, 2013

Explorer Geophysical Corner By Evan Staples,Kurt Marfurt,Satinder Chopra

Testing Curvature's Impact on Fractures

Fracture zones can be critical to improving or creating sufficient porosity and permeability in hydrocarbon reservoirs – with strain, along with lithology and thickness being the major controls.

Added on 01 July, 2013

Explorer Emphasis Article By Louise Durham

Geomechanics Helps Solve Horizontal Woes

Think fast: A new risk-based approach to geomechanics is being used to help solve horizontal drilling problems.

Added on 01 July, 2013

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

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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