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Fakcharoenphol P.,Royal Dutch Shell | Torcuk M.,EOG Resources. Inc. | Kazemi H.,Colorado School of Mines | Wu Y.-S.,Colorado School of Mines
Journal of Natural Gas Science and Engineering | Year: 2016

Some shale gas and oil wells undergo month-long shut-in times after multi-stage hydraulic fracturing well stimulation. Field data indicate that in some wells, such shut-in episodes surprisingly increase the gas and oil flow rate. In this paper, we report a numerical simulation study that supports such observations and provides a potentially viable underlying imbibition and drainage mechanism. In the simulation, the shale reservoir is represented by a triple-porosity fracture-matrix model, where the fracture forms a continuum of interconnected network created during the well stimulation while the organic and inorganic matrices are embedded in the fracture continuum. The effect of matrix wettability, capillary pressure, relative permeability, and osmotic pressure, that is, chemical potential characteristics are included in the model.The simulation results indicate that the early lower flow rates are the result of obstructed fracture network due to high water saturation. This means that the injected fracturing fluid fills such fractures and blocks early gas or oil flow. Allowing time for the gravity drainage and imbibition of injected fluid in the fracture-matrix network is the key to improving the hydrocarbon flow rate during the shut-in period. © 2016 Elsevier B.V. Source


Cox R.T.,University of Memphis | Harris J.,Millsaps College | Forman S.,University of Illinois at Chicago | Brezina T.,University of Memphis | And 3 more authors.
Special Paper of the Geological Society of America | Year: 2013

A fundamental goal of intraplate tectonics research is to understand the role of crustal discontinuities in the distribution of Quaternary surface ruptures. Geophysical studies of southern North America on the Gulf of Mexico Coastal Plain reveal a buried Cambrian craton margin (Alabama-Oklahoma transform) that strikes southeast beneath Mesozoic and Cenozoic passive-margin sediments and Paleozoic thrust sheets. Seismic-refl ection profiles show a graben system (Saline River fault zone) related to an episode of Triassic rifting above this transform margin during initial opening of the Gulf of Mexico. Post-Triassic reactivation of the Saline River fault zone produced normal and reverse faulting and strike-slip fl ower structures that can be linked to Quaternary surface deformation. We investigated surface and shallow Quaternary faulting along the Saline River fault system in south-central North America. Our field sites show late Pleistocene to late Holocene surface and near-surface deformation along lineaments and scarps of the Saline River fault zone. Age constraints from three sites are consistent with a surface rupture as long as 70 km ca. 6-5 ka. Mid-Holocene sand blows in the region may record strong shaking from such a large earthquake about the same time, but available ages provide only broad constraints on the timing of large earthquakes in the Saline River fault zone. The Saline River fault zone significantly expands the known area of paleoseismicity in midcontinent North America. This study builds upon our understanding of the Saline River fault zone's relationship to a transform craton margin and thus advances our understanding of active intraplate deformation. © 2012 The Geological Society of America. All rights reserved. Source


Cho Y.,Colorado School of Mines | Apaydin O.G.,EOG Resources. Inc. | Ozkan E.,Colorado School of Mines
Proceedings - SPE Annual Technical Conference and Exhibition | Year: 2012

This paper presents the results of an experimental study of pressure-dependent natural-fracture permeability in tight, unconventional reservoirs. Bakken cores are used in the experiments. For the purpose of this paper, pressure-related permeability losses in hydraulic fractures and matrix system are not considered. Experimental data are used to screen the stress-dependent matrix-permeability correlations available in the literature for application to shale fractures. Selected correlations are matched with the data to delineate the reasonable ranges of the correlation coefficients for shale fractures. The applications of the correlations over practical ranges of pressure drop in shale reservoirs indicate over 80% reduction in fracture permeability, with most of the permeability loss occurring during the initial pressure drop. To appraise the effect of pressure-dependent natural-fracture permeability on shale-gas production, experimentally developed correlations are incorporated in an analytical model of a fractured horizontal well surrounded by a stimulated reservoir volume. The model is used to history match the performances of two wells in the Barnett and Haynesville formations. It is shown that the effect of pressure-dependent natural-fracture permeability on shale-gas-well production is a function of the permeability of the matrix system. If the matrix system is too tight, then the retained permeability of the natural fractures may still be sufficient for the available volume of the fluid when the system pressure drops. Copyright 2012, Society of Petroleum Engineers. Source


Cox R.T.,University of Memphis | Hall J.L.,University of Memphis | Gardner C.S.,EOG Resources. Inc.
Tectonophysics | Year: 2013

Although the northwest-striking Saline River fault system of southeastern Arkansas is not defined by microseismicity, it is associated with sand blows and shows evidence of Pleistocene and Holocene surface ruptures, suggesting a significant seismogenic potential. This fault system is within the northern Gulf of Mexico interior coastal plain, a region only recently recognized as containing seismogenic faults. To better characterize this active fault system, we reconstructed its post-Paleozoic history using petroleum and coal industry wire-line well log and seismic reflection subsurface data.The Saline river fault system initiated as a series of northwest-striking grabens during Triassic/Jurassic uplift and incipient Gulf of Mexico rifting along the basement Alabama-Oklahoma transform margin of the North American Proterozoic craton. During post-rift subsidence, these grabens were buried by Gulf sediments until mid-Cretaceous uplift and igneous activity resulted in minor extensional reactivation of graben faults. Faulting style changed from extension to transpression during the Late Cretaceous due to compression of eastern North America as the North Atlantic rapidly widened and due to thermal weakening of the Alabama-Oklahoma transform lithospheric discontinuity as it obliquely crossed a mantle hot spot. In the Late Cretaceous, graben faults experienced contractional reactivation and steep, deeply-rooted transpressional faults developed within and parallel to the graben system. These transpressional faults locally displace Eocene, Pleistocene, and Holocene sediments.Fault activity continues on the Saline River fault system due to thin crust along the Alabama-Oklahoma transform and to high heat flow, which act together to weaken the crust and promote seismogenic tectonism. The fault system may lack appreciable microseismicity because the aftershock sequence of the last large earthquake has had time to dissipate. © 2013 Elsevier B.V. Source


Dunlap D.B.,University of Texas at Austin | Wood L.J.,University of Texas at Austin | Weisenberger C.,EOG Resources. Inc. | Jabour H.,National Office of Hydrocarbons and Mining
AAPG Bulletin | Year: 2010

The lower continental slope of Morocco's west coast consists of Triassic-age salt manifested in the form of diapirs, tongues, sheets, canopies, and toe thrusts. Active salt diapirism and regional tectonics greatly influence the morphology of the modern sea floor, forming a severely rugose expression with ongoing minibasin development and episodic submarine failure. Detailed mapping of a 1064-km2 (411 -mi2) seismic survey acquired in the Safi Haute Mer area revealed that Jurassic to Holocene salt mobilization continually affected distribution of sediment, causing a range of depositional flow styles, from slumps to sheet slides and mass-transport complexes (MTCs). Large sediment waves (20 km [12 mi] long, 1.5-km [0.9-mi] wavelength) were also documented at the end of the Aptian. An east-west-trending structural anticline downdip of the salt activated during initiation of the Atlas uplift in the latest Cretaceous to earliest Tertiary and shaped much of the lower slope into the Tertiary with a persistent canyon system and slope channels. The largest of the debris flows is a Cretaceous-age MTC, a 500-m (1640-ft)thick flow that spans an area of up to 20,000 km2 (7722 mi2). Composing the MTC are (1) chaotic, mounded seismic faciès; (2) internal syndepositional thrusts; and (3) transported megablocks (3.3 km2 [1.3 mi 2]) witb preserved internal stratigraphy. The MTC originated from an upslope collapse of a narrow shelf during the earliest phases of the Alpine orogeny. Copyright ©2010. The American Assotiation of Petroleum Geologists. All rights reserved. Source

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