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Fracture imaging with converted elastic waves

Description: This paper examines the seismic signatures of discrete, finite-length fractures, and outlines an approach for elastic, prestack reverse-time imaging of discrete fractures. The results of this study highlight the importance of incorporating fracture-generated P-S converted waves into the imaging method, and presents an alternate imaging condition that can be used in elastic reverse-time imaging when a direct wave is recorded (e.g., for crosswell and VSP acquisition geometries).
Date: May 29, 2001
Creator: Nihei, K.T.; Nakagawa, S. & Myer, L.R.
Partner: UNT Libraries Government Documents Department

Quasi-static analysis of elastic behavior for some systems having higher fracture densities.

Description: Elastic behavior of geomechanical systems with interacting (but not intersecting) fractures is treated using generalizations of the Backus and the Schoenberg-Muir methods for analyzing layered systems whose layers are intrinsically anisotropic due to locally aligned fractures. By permitting the axis of symmetry of the locally anisotropic compliance matrix for individual layers to differ from that of the layering direction, we derive analytical formulas for interacting fractured regions with arbitrary orientations to each other. This procedure provides a systematic tool for studying how contiguous, but not yet intersecting, fractured domains interact, and provides a direct (though approximate) means of predicting when and how such interactions lead to more dramatic weakening effects and ultimately to failure of these complicated systems. The method permits decomposition of the system elastic behavior into specific eigenmodes that can all be analyzed, and provides a better understanding about which of these specific modes are expected to be most important to the evolving failure process.
Date: October 15, 2009
Creator: Berryman, J.G. & Aydin, A.
Partner: UNT Libraries Government Documents Department

Experimental and Analytical Research on Fracture Processes in ROck

Description: Experimental studies on fracture propagation and coalescence were conducted which together with previous tests by this group on gypsum and marble, provide information on fracturing. Specifically, different fracture geometries wsere tested, which together with the different material properties will provide the basis for analytical/numerical modeling. INitial steps on the models were made as were initial investigations on the effect of pressurized water on fracture coalescence.
Date: February 27, 2009
Creator: Einstein, Herbert H..; Miller, Jay & Silva, Bruno
Partner: UNT Libraries Government Documents Department

Results of a coupled fracture-flow test at the 0.5-m scale

Description: This report presents progress made on two experiments on 0.5-meter-scale blocks to determine thermohydromechanical (THM) behavior of fractured rock. We first present results for an experiment on sample SB3, including data for flow measurements through a horizontally oriented, artifical (saw-cut) fracture at a series of differential fluid pressures and temperatures under uniaxial stress conditions up to 14 MPa. We then present the experiment design and a progress report on the assembly of experiment SB4, flow through a vertically oriented fracture intersected by a line heat source.
Date: August 14, 1998
Creator: Costantino, M. S.
Partner: UNT Libraries Government Documents Department

Tracer mixing at fracture intersections

Description: Discrete network models are one of the approaches used to simulate a dissolved contaminant, which is usually represented as a tracer in modeling studies, in fractured rocks. The discrete models include large numbers of individual fractures within the network structure, with flow and transport described on the scale of an individual fracture. Numerical simulations for the mixing characteristics and transfer probabilities of a tracer through a fracture intersection are performed for this study. A random-walk, particle-tracking model is applied to simulate tracer transport in fracture intersections by moving particles through space using individual advective and diffusive steps. The simulation results are compared with existing numerical and analytical solutions for a continuous intersection over a wide range of Peclet numbers. This study attempts to characterize the relative concentration at the outflow branches for a continuous intersection with different flow fields. The simulation results demonstrate that the mixing characteristics at the fracture intersections are a function not only of the Peclet number but also of the flow field pattern.
Date: February 10, 2001
Creator: Li, Guomin
Partner: UNT Libraries Government Documents Department

3-D Reservoir and Stochastic Fracture Network Modeling for Enhanced Oil Recovery, Circle Ridge Phosphoria/Tensleep Reservoir, and River Reservation, Arapaho and Shoshone Tribes, Wyoming

Description: The goal of this project is to improve the recovery of oil from the Circle Ridge Oilfield, located on the Wind River Reservation in Wyoming, through an innovative integration of matrix characterization, structural reconstruction, and the characterization of the fracturing in the reservoir through the use of discrete fracture network models.
Date: September 9, 2002
Creator: La Pointe, Paul; Parney, Robert; Eiben, Thorsten; Dunleavy, Mike; Whitney, John & Eubanks, Darrel
Partner: UNT Libraries Government Documents Department

3-D Reservoir and Stochastic Fracture Network Modeling for Enhanced Oil Recovery, Circle Ridge Phosphoria/Tensleep Reservoir, and River Reservation, Arapaho and Shoshone Tribes, Wyoming

Description: The goal of this project is to improve the recovery of oil from the Circle Ridge Oilfield, located on the Wind River Reservation in Wyoming, through an innovative integration of matrix characterization, structural reconstruction, and the characterization of the fracturing in the reservoir through the use of discrete fracture network models.
Date: September 9, 2002
Creator: Pointe, La; Paul; Parney, Robert; Eiben, Thorsten; Dunleavy, Mike & Whitney, John
Partner: UNT Libraries Government Documents Department

3-D Reservoir and Stochastic Fracture Network Modeling for Enhanced Oil Recovery, Circle Ridge Phosphoria/Tensleep Reservoir, and River Reservation, Arapaho and Shoshone Tribes, Wyoming

Description: The goal of this project is to improve the recovery of oil from the Circle Ridge Oilfield, located on the Wind River Reservation in Wyoming, through an innovative integration of matrix characterization, structural reconstruction, and the characterization of the fracturing in the reservoir through the use of discrete fracture network models.
Date: September 9, 2002
Creator: La Pointe, Paul R. & Hermanson, Jan
Partner: UNT Libraries Government Documents Department

3-D Reservoir and Stochastic Fracture Network Modeling for Enhanced Oil Recovery, Circle Ridge Phosphoria/Tensleep Reservoir, and River Reservation, Arapaho and Shoshone Tribes, Wyoming

Description: The goal of this project is to improve the recovery of oil from the Circle Ridge Oilfield, located on the Wind River Reservation in Wyoming, through an innovative integration of matrix characterization, structural reconstruction, and the characterization of the fracturing in the reservoir through the use of discrete fracture network models.
Date: September 9, 2002
Creator: La Pointe, Paul R.; Hermanson, Jan & Eiben, Thorsten
Partner: UNT Libraries Government Documents Department

TEM Study of Fracturing in Spherical and Plate-like LiFePO4Particles

Description: An investigation of fracturing in LiFePO{sub 4} particles as a function of the particle morphology and history is presented. Two types of samples, one subjected to electrochemical cycling and another to chemical delithiation are compared. We observe the formation of micro fractures parallel to low indexed lattice planes in both samples. The fracture surfaces are predominantly parallel to (100) planes in the chemically delithiated powder and (100) and (010) planes in the electrochemically cycled powder. A consideration of the threshold stresses for dislocation glide shows that particle geometry plays an important role in the observed behavior.
Date: December 20, 2007
Creator: Gabrisch, H.; Wilcox, J. & Doeff, M.M.
Partner: UNT Libraries Government Documents Department

DNAPL invasion into a partially saturated dead-end fracture

Description: The critical height for DNAPL entry into a partially watersaturated, dead-end fracture is derived and compared to laboratoryobservations. Experiments conducted in an analog, parallel-plate fracturedemonstrate that DNAPL accumulates above the water until the height ofthe DNAPL overcomes the sum of the capillary forces at the DNAPL-airinterface and at the DNAPL-water interface. These experiments also showthat DNAPL preferentially enters the water at locations where DNAPL haspreviously entered, and the entry heights for these subsequent entriesare lower than the heights measured for the initial invasion. The wettingcontact angle at the DNAPL-water interface becomes larger at thelocations where the DNAPL has already entered the water because ofresidual DNAPL on the fracture walls, which results in lowering thecritical entry height at those locations. The experiments alsodemonstrate that a DNAPL lens can remain nearly immobile above the waterfor a period of time before eventually redistributing itself and enteringthe water.
Date: June 17, 2004
Creator: gwsu@lbl.gov
Partner: UNT Libraries Government Documents Department

Fracture Characteristics in a Disposal Pit on Mesita del Buey, Los Alamos National Laboratory

Description: The characteristics of fractures in unit 2 of the Tshirege Member of the Bandelier Tuff were documented in Pit 39, a newly excavated 13.7 m deep disposal pit at Material Disposal Area G on Mesita del Buey. The average spacing between fractures is about 1.0 to 1.3 m, the average fracture aperture is about 3 to 5 mm, and the average fracture dip is about 76o to 77o. Fracture spacing and dip in Pit 39 are generally consistent with that reported from other fracture studies on the Pajarito Plateau, although the fracture apertures in Pit 39 are less than reported elsewhere. Measured fracture orientations are strongly affected by biases imparted by the orientations of the pit walls, which, combined with a small data set, make identification of potential preferred orientations dlfflcult. The most prominent fracture orientations observed in Pit 39, about E-W and N20E, are often not well represented elsewhere on the Pajarito Plateau. Fracture fills contain smectite to about 3 m depth, and calcite and opal may occur at all depths, principally associated with roots or root fossils (rhizoliths). Roots of pifion pine extend in fractures to the bottom of the pit along the north side, perhaps indicating a zone of preferred infiltration of water. Finely powdered tuff with clay-sized particles occurs within a number of fractures and may record abrasive disaggregation associated with small amounts of displacement on minor local faults.
Date: December 1, 1998
Creator: Vaniman, David T. & Reneau, Steven L.
Partner: UNT Libraries Government Documents Department

Economic Recovery of Oil Trapped at Fan Margins Using High Angle Wells and Multiple Hydraulic Fractures

Description: The distal fan margin in the northeast portion of the Yowlumne field contains significant reserves but is not economical to develop using vertical wells. Numerous interbedded shales and deteriorating rock properties limit producibility. In addition, extreme depths (13,000 ft) present a challenging environment for hydraulic fracturing and artificial lift. Lastly, a mature waterflood increases risk because of the uncertainty with size and location of flood fronts. This project attempts to demonstrate the effectiveness of exploiting the distal fan margin of this slope-basin clastic reservoir through the use of a high-angle well completed with multiple hydraulic-fracture treatments. The combination of a high-angle (or horizontal) well and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional vertical wells while maintaining vertical communication between thin interbedded layers and the wellbore. The equivalent production rate and reserves of three vertical wells are anticipated at one-half to two-thirds the cost.
Date: May 30, 1997
Creator: Laue, Mike L.
Partner: UNT Libraries Government Documents Department

Advanced Reservoir Characterization and Evaluation of CO2 Gravity Drainage in the Naturally Fractured Spraberry Reservoir

Description: Natural fractures exert a strong influence over oil production in Spraberry Trend Area reservoirs in the Permian Basin of west Texas. The importance of the fracture network has been known since the 1950s, but until recently, there has been very little detailed study of the fractures themselves. In 1996, a horizontal Spraberry well was cored as part of a DOE Class III Field Demonstration Project. Fractures from the horizontal core as well as other fractures encountered in vertical Spraberry cores were analyzed in detail for information on both large scale features including orientation and spacing and small-scale features such as the relationships between fracture mineralization and matrix rock composition. At least three sets of fractures are found within the upper and middle Spraberry cores. These sets have distinct orientations, spacing, mineralization, distribution with respect to lithology, and surface characteristics (Lorenz, 1997). Fractures found in the 1U zone of the upper Spraberry have a NE strike, and tend to be partly mineralized with barite, quartz, and dolomite. Distribution of these mineral phases can greatly affect conductivity between the fractures and the rock matrix. The 5U zone of the upper Spraberry contains fractures with NNE and ENE orientations. The NNE set of fractures has stepped fracture surfaces indicating a shear origin, and minor amounts of quartz and dolomite mineralization. The ENE fracture set has smooth planar surfaces of tension origin with some calcite mineralization present. Natural fractures in black shales overlying both the 1U and the 5U have an ENE orientation similar to unmineralized fractures in the 5U. No fractures were encountered in similar shales underlying reservoir zones. A set of hairline fractures, most completely healed with calcite cement was also found in some Middle Spraberry cores. The unique nature of each of these fracture sets implies that fracturing probably occurred as ...
Date: December 17, 1997
Creator: Schechter, David S.
Partner: UNT Libraries Government Documents Department

SIZE SCALING RELATIONSHIPS IN FRACTURE NETWORKS

Description: Work focused on the program development phase, which has been successfully completed. A revised timetable has been prepared that reflects the June start date and other modifications associated with internal budgeting problems and the actual versus proposed start dates.
Date: July 27, 1998
Creator: WILSON, TOM
Partner: UNT Libraries Government Documents Department

Measurement of Fracture Aperture Fields Using Ttransmitted Light: An Evaluation of Measurement Errors and their Influence on Simulations of Flow and Transport through a Single Fracture

Description: Understanding of single and multi-phase flow and transport in fractures can be greatly enhanced through experimentation in transparent systems (analogs or replicas) where light transmission techniques yield quantitative measurements of aperture, solute concentration, and phase saturation fields. Here we quanti@ aperture field measurement error and demonstrate the influence of this error on the results of flow and transport simulations (hypothesized experimental results) through saturated and partially saturated fractures. find that precision and accuracy can be balanced to greatly improve the technique and We present a measurement protocol to obtain a minimum error field. Simulation results show an increased sensitivity to error as we move from flow to transport and from saturated to partially saturated conditions. Significant sensitivity under partially saturated conditions results in differences in channeling and multiple-peaked breakthrough curves. These results emphasize the critical importance of defining and minimizing error for studies of flow and transpoti in single fractures.
Date: May 6, 1999
Creator: Detwiler, Russell L.; Glass, Robert J. & Pringle, Scott E.
Partner: UNT Libraries Government Documents Department

Random polycrystals of grains containing cracks: Model ofquasistatic elastic behavior for fractured systems

Description: A model study on fractured systems was performed using aconcept that treats isotropic cracked systems as ensembles of crackedgrains by analogy to isotropic polycrystalline elastic media. Theapproach has two advantages: (a) Averaging performed is ensembleaveraging, thus avoiding the criticism legitimately leveled at mosteffective medium theories of quasistatic elastic behavior for crackedmedia based on volume concentrations of inclusions. Since crack effectsare largely independent of the volume they occupy in the composite, sucha non-volume-based method offers an appealingly simple modelingalternative. (b) The second advantage is that both polycrystals andfractured media are stiffer than might otherwise be expected, due tonatural bridging effects of the strong components. These same effectshave also often been interpreted as crack-crack screening inhigh-crack-density fractured media, but there is no inherent conflictbetween these two interpretations of this phenomenon. Results of thestudy are somewhat mixed. The spread in elastic constants observed in aset of numerical experiments is found to be very comparable to the spreadin values contained between the Reuss and Voigt bounds for thepolycrystal model. However, computed Hashin-Shtrikman bounds are much tootight to be in agreement with the numerical data, showing thatpolycrystals of cracked grains tend to violate some implicit assumptionsof the Hashin-Shtrikman bounding approach. However, the self-consistentestimates obtained for the random polycrystal model are nevertheless verygood estimators of the observed average behavior.
Date: July 8, 2006
Creator: Berryman, James G. & Grechka, Vladimir
Partner: UNT Libraries Government Documents Department