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Trondheim, Norway

Tora G.,Norwegian University of Science and Technology | Hansen A.,Norwegian University of Science and Technology | Oren P.-E.,Numerical Rocks AS
Proceedings - SPE Annual Technical Conference and Exhibition | Year: 2010

We present numerical results of electrical resistivity of two-phase flow in reservoir rocks using a dynamic network model. The model accounts for viscous and capillary forces, as well as wetting layers in the crevices of the pore space. It can be used as a unified model for drainage, imbibition and steady-state displacement. We use the model to study viscous effects on electrical resistivity for two-phase flow under strongly water-wet conditions. The pore network is extracted from a realistic pore space of a sandstone. For unsteady drainage and imbibition, our numerical results display capillary number dependent non-Archie behavior and hysteresis of the resistivity index. For steady-state displacement the resistivity index exhibits no significant hysteresis. For increasing capillary number we observe a higher degree of non-Archie (negative curvature) behavior. The simulated data are compared with relevant experimental data, and are in good agreement. Our conclusion is that the dynamic network model successfully reproduces viscous effects on the resistivity index in drainage, imbibition and steady-state displacement processes. Copyright 2010, Society of Petroleum Engineers. Source

Tora G.,Norwegian University of Science and Technology | Oren P.-E.,Numerical Rocks AS | Hansen A.,Norwegian University of Science and Technology
Transport in Porous Media | Year: 2012

We present a dynamic model of immiscible two-phase flow in a network representation of a porous medium. The model is based on the governing equations describing two-phase flow in porous media, and can handle both drainage, imbibition, and steady-state displacement. Dynamic wetting layers in corners of the pore space are incorporated, with focus on modeling resistivity measurements on saturated rocks at different capillary numbers. The flow simulations are performed on a realistic network of a sandpack which is perfectly water-wet. Our numerical results show saturation profiles for imbibition in agreement with experiments. For free spontaneous imbibition we find that the imbibition rate follows the Washburn relation, i. e., the water saturation increases proportionally to the square root of time. We also reproduce rate effects in the resistivity index for drainage and imbibition. © 2011 Springer Science+Business Media B.V. Source

Fichler C.,Statoil | Odinsen T.,Statoil | Rueslatten H.,Numerical Rocks AS | Olesen O.,Geological Survey of Norway | And 2 more authors.
Tectonophysics | Year: 2011

A new crustal model for the northern North Sea was developed by gravity and magnetic modeling along the deep seismic line NSDP84-1. Utilizing vertical gradients allowed distinguishing between shallow and deep crustal sources. The upper crust is characterized by low magnetic susceptibilities and low densities, which is typical for felsic rocks. A new finding was that the deep crust below the western Viking Graben and the East Shetland Basin is the source of high magnetic anomalies combined with low gravity anomalies, which was interpreted to represent rocks with very high magnetic susceptibilities and low to intermediate densities. Such rock parameters may indicate serpentinites, but intermediate intrusives or a combination of both is also possible. Honoring the string of three near equidistant magnetic maxima, which follow the trend of the NNE-SSW striking East Shetland Basin in the map plane, it is suggested that this area is part of an island arc of the Iapetus Ocean which has been assembled during the collision between Laurentia and Baltica in late Silurian times. Partly serpentinized peridotites and intermediate intrusives will relate in such a model to slab dehydration of the subducting oceanic plate below the island arc. These inherited or synorogenic serpentinites are expected to persist in the geothermal regime of the Caledonian orogeny to a depth of at least 50. km. Increased heat flow by later rift phases will have caused metamorphism of the remaining serpentinites to meta-peridotites at depth below the present day Moho. Fluid release related to dehydration of the serpentinites may have triggered further serpentinization of the inherited, partly serpentinized rocks at shallower depth. An alternative origin for the suggested serpentinites, valid only for the area under the western part of the Viking Graben, may be synrift serpentinization due to the heavy faulting during the Jurassic rift phase. © 2011 Elsevier B.V. Source

Weltje G.J.,Technical University of Delft | Alberts L.J.H.,Numerical Rocks AS
Sedimentary Geology | Year: 2011

The question being tackled in this study is to which extent grain rearrangement contributes to porosity reduction in very well sorted quartzose sands (ideal reservoir sands). A numerical model, RAMPAGE (an acronym of random packing generator), has been developed to address this long-standing problem. RAMPAGE represents a synthesis of various algorithms designed to simulate packing of equal-sized spheres, which have been used to represent ideal solids, liquids, and gases, as well as natural porous media. The results of RAMPAGE simulations compare favourably to theoretical and experimental data from various disciplines and allow delineation of the field of gravitationally stable random packing of equal-sized spheres in the 2-D state space of porosity (P) versus mean coordination number (N). Three end-member packing states have been identified: random loose packing (RLP: P= 45.4%, N= 5.2), random close packing (RCP: P= 36.3%, N= 7.0), and bridged random close packing (Bridged RCP: P= 39.5%, N= 5.2). Unlike previously proposed models, RAMPAGE can simulate the transition from RLP to any other point in the stability field. The RLP state is fully consistent with wet-packed porosities of synthetic sands with lognormal mass-size distributions reported in the literature. The much higher in-situ porosity values reported for modern (air-packed) sands are unlikely to be preserved at depth on geological time scales. Data on the relation between intergranular volume and burial depth indicate that the observed intergranular volume reduction in the upper ~. 800. m of the sediment column corresponds to the evolution of RLP to RCP, and is thus fully explained by non-destructive grain rearrangement. © 2011 Elsevier B.V. Source

Roth S.,Numerical Rocks AS | Biswal B.,University of Stuttgart | Biswal B.,University of Delhi | Afshar G.,University of Stuttgart | And 4 more authors.
AAPG Bulletin | Year: 2011

A continuum-based pore-scale representation of a dolomite reservoir rock is presented, containing several orders of magnitude in pore sizes within a single rock model. The macroscale rock fabric from a low-resolution x-ray microtomogram was combined with microscale information gathered from high-resolution two-dimensional electron microscope images. The low-resolution x-ray microtomogram was segmented into six separate rock phases in terms of mineralogy, matrix appearances, and open- versus crystal-filled molds. These large-scale rock phases were decorated (modeled) with geometric objects, such as different dolomite crystal types and anhydrite, according to the high-resolution information gathered from the electron microscope images. This procedure resulted in an approximate three-dimensional representation of the diagenetically transformed rock sample with respect to dolomite crystal sizes, porosity, appearance, and volume of different matrix phases and pore/matrix/cement ratio. The resulting rock model contains a pore-size distribution ranging from moldic macropores (several hundred micrometers in diameter) down to mudstone micropores (<1 μm in diameter). This allows us to study the effect and contribution of different pore classes to the petrophysical properties of the rock. Higher resolution x-ray tomographs of the same rock were used as control volumes for the pore-size distribution of the model. The pore-size analysis and percolation tests performed in three dimensions at various discretization resolutions indicate pore-throat radii of 1.5 to 6 μm for the largest interconnected pore network. This also highlights the challenge to determine appropriate resolutions for x-ray imaging when the exact rock microstructure is not known. Copyright ©2011. The American Assodation of Petroleum Geologists. All rights reserved. Source

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