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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

A modified invasion percolation model for low-capillary number immiscible displacements in horizontal rough-walled fractures: Influence of local in-plane

Description: The authors develop and evaluate a modified invasion percolation (MIP) model for quasi-static immiscible displacement in horizontal fractures. The effects of contact angle, local aperture field geometry, and local in-plane interracial curvature between phases are included in the calculation of invasion pressure for individual sites in a discretized aperture field. This pressure controls the choice of which site is invaded during the displacement process and hence the growth of phase saturation structure within the fracture. To focus on the influence of local in-plane curvature on phase invasion structure, they formulate a simplified nondimensional pressure equation containing a dimensionless curvature number (C) that weighs the relative importance of in-plane curvature and aperture-induced curvature. Through systematic variation of C, they find in-plane interracial curvature to greatly affect the phase invasion structure. As C is increased from zero, phase invasion fronts transition from highly complicated (IP results) to microscopically smooth. In addition, measurements of fracture phase saturations and entrapped cluster statistics (number, maximum size, structural complication) show differential response between wetting and nonwetting invasion with respect to C that is independent of contact angle hysteresis. Comparison to experimental data available at this time substantiates predicted behavior.
Date: January 28, 2000
Creator: GLASS JR.,ROBERT J.; NICHOLL,MICHAEL J. & YARRINGTON,LANE
Partner: UNT Libraries Government Documents Department

San Juan Fracture Characterization Project: Status and current results

Description: The overall objectives of this report are to extend current state-of-the-art 3-D imaging to extract the optimal information for fracture quantification and to develop next generation capability in fracture imaging for true 3-D imaging of the static and dynamic fracture properties.
Date: February 26, 2001
Creator: Majer, E.L.; Daley, T.M.; Myer, L.R.; Nihei, K.; Queen, J.; Sinton, J. et al.
Partner: UNT Libraries Government Documents Department

Factors controlling satiated relative permeability in a partially-saturated horizontal fracture

Description: Recent work demonstrates that phase displacements within horizontal fractures large with respect to the spatial correlation length of the aperture field lead to a satiated condition that constrains the relative permeability to be less than one. The authors use effective media theory to develop a conceptual model for satiated relative permeability, then compare predictions to existing experimental measurements, and numerical solutions of the Reynolds equation on the measured aperture field within the flowing phase. The close agreement among all results and data show that for the experiments considered here, in-plane tortuosity induced by the entrapped phase is the dominant factor controlling satiated relative permeability. They also find that for this data set, each factor in the conceptual model displays an approximate power law dependence on the satiated saturation of the fracture.
Date: February 16, 2000
Creator: NICHOLL,M.J.; RAJARAM,H. & GLASS JR.,ROBERT J.
Partner: UNT Libraries Government Documents Department

Stress-dependent permeability of fractured rock masses: A numerical study

Description: We investigate the stress-dependent permeability issue in fractured rock masses considering the effects of nonlinear normal deformation and shear dilation of fractures using a two-dimensional distinct element method program, UDEC, based on a realistic discrete fracture network realization. A series of ''numerical'' experiments were conducted to calculate changes in the permeability of simulated fractured rock masses under various loading conditions. Numerical experiments were conducted in two ways: (1) increasing the overall stresses with a fixed ratio of horizontal to vertical stresses components; and (2) increasing the differential stresses (i.e., the difference between the horizontal and vertical stresses) while keeping the magnitude of vertical stress constant. These numerical experiments show that the permeability of fractured rocks decreases with increased stress magnitudes when the stress ratio is not large enough to cause shear dilation of fractures, whereas permeability increases with increased stress when the stress ratio is large enough. Permeability changes at low stress levels are more sensitive than at high stress levels due to the nonlinear fracture normal stress-displacement relation. Significant stress-induced channeling is observed as the shear dilation causes the concentration of fluid flow along connected shear fractures. Anisotropy of permeability emerges with the increase of differential stresses, and this anisotropy can become more prominent with the influence of shear dilation and localized flow paths. A set of empirical equations in closed-form, accounting for both normal closure and shear dilation of the fractures, is proposed to model the stress-dependent permeability. These equations prove to be in good agreement with the results obtained from our numerical experiments.
Date: April 30, 2004
Creator: Min, Ki-Bok; Rutqvist, J.; Tsang, Chin-Fu & Jing, Lanru
Partner: UNT Libraries Government Documents Department

The interplay of fractures and sedimentary architecture: Natural gas from reservoirs in the Molina sandstones, Piceance Basin, Colorado

Description: The Molina Member of the Wasatch Formation produces natural gas from several fields along the Colorado River in the Piceance Basin, northwestern Colorado. The Molina Member is a distinctive sandstone that was deposited in a unique fluvial environment of shallow-water floods. This is recorded by the dominance of plane-parallel bedding in many of the sandstones. The Molina sandstones crop out on the western edge of the basin, and have been projected into the subsurface and across the basin to correlate with thinner sandy units of the Wasatch Formation at the eastern side of the basin. Detailed study, however, has shown that the sedimentary characteristics of the type-section Molina sandstones are incompatible with a model in which the eastern sandstones are its distal facies equivalent. Rather, the eastern sandstones represent separate and unrelated sedimentary systems that prograded into the basin from nearby source-area highlands. Therefore, only the subsurface {open_quotes}Molina{close_quotes} reservoirs that are in close proximity to the western edge of the basin are continuous with the type-section sandstones. Reservoirs in the Grand Valley and Rulison gas fields were deposited in separate fluvial systems. These sandstones contain more typical fluvial sedimentary structures such as crossbeds and lateral accretion surfaces. Natural fractures play an important role in enhancing the conductivity and permeability of the Molina and related sandstones of the Wasatch Formation.
Date: March 1, 1997
Creator: Lorenz, J.C.
Partner: UNT Libraries Government Documents Department

Predictive Modeling of MIU3-MIU2 Interference Tests

Description: The goal of this project is to predict the drawdown that will be observed in specific piezometers placed in the MIU-2 borehole due to pumping at a single location in the MIU-3 borehole. These predictions will be in the form of distributions obtained through multiple forward runs of a well-test model. Specifically, two distributions will be created for each pumping location--piezometer location pair: (1) the distribution of the times to 1.0 meter of drawdown and (2) the distribution of the drawdown predicted after 12 days of pumping at a discharge rates of 25, 50, 75 and 100 l/hr. Each of the steps in the pumping rate lasts for 3 days (259,200 seconds). This report is based on results that were presented at the Tono Geoscience Center on January 27th, 2000, which was approximately one week prior to the beginning of the interference tests. Hydraulic conductivity (K), specific storage (S{sub s}) and the length of the pathway (L{sub p}) are the input parameters to the well-test analysis model. Specific values of these input parameters are uncertain. This parameter uncertainty is accounted for in the modeling by drawing individual parameter values from distributions defined for each input parameter. For the initial set of runs, the fracture system is assumed to behave as an infinite, homogeneous, isotropic aquifer. These assumptions correspond to conceptualizing the aquifer as having Theis behavior and producing radial flow to the pumping well. A second conceptual model is also used in the drawdown calculations. This conceptual model considers that the fracture system may cause groundwater to move to the pumping well in a more linear (non-radial) manner. The effects of this conceptual model on the drawdown values are examined by casting the flow dimension (F{sub d}) of the fracture pathways as an uncertain variable between 1.0 (purely linear flow) ...
Date: February 1, 2001
Creator: MCKENNA, SEAN A. & ROBERTS, RANDALL M.
Partner: UNT Libraries Government Documents Department

Discussion of DNAPL Migration through a Fractured Perching Layer

Description: The visualization study of 1,1,1-trichloroethane (TCA) infiltration described by Stephens et al. (1998) was an elegant design, clearly demonstrating DNAPL behavior encountering a fractured perched layer. I question, however, their interpretation, stated in both abstract and conclusions, that rapid DNAPL penetration of the fracture was "in contrast to existing mathematical solutions of hydrostatic initial conditions and full saturation below the fracture." I also have a comment regarding the experimental conditions.
Date: January 13, 1999
Creator: Tuck, D.M.
Partner: UNT Libraries Government Documents Department

Naturally fractured tight gas reservoir detection optimization. Annual report, August 1994--July 1995

Description: This report details the field work undertaken Blackhawk Geosciences and Lynn, Inc. during August 1994 to July 1995 at a gas field in the Wind River Basin in central Wyoming. The work described herein consisted of four parts: 9C VSP in a well at the site; additional processing of the previously recorded 3D P-wave survey on the site and Minivibrator testing; and planning and acquisition of a 3-D, 3-C seismic survey. The objectives of all four parts were to characterize the nature of anisotropy in the reservoir. With the 9C VSP, established practices were used to achieve this objective in the immediate vicinity of the well. The additional processing of the 3-D uses developmental techniques to determine areas of fractures in 3-D surveys. With the multicomponent studies, tests were conducted to establish the feasibility of surface recording of the anisotropic reservoir rocks. The 3-D, 3-C survey will provide both compressional and shear wave data sets over areas of known fracturing to verify the research.
Date: September 1, 1995
Partner: UNT Libraries Government Documents Department

Fracture characterization and discrimination criteria for karst and tectonic fractures in the Ellenburger Group, West Texas: Implications for reservoir and exploration models

Description: In the Ellenburger Group fractured dolomite reservoirs of West Texas, it is extremely difficult to distinguish between multiple phases of karst-related fracturing, modifications to the karst system during burial, and overprinting tectonic fractures. From the analyses of drill core, the authors developed criteria to distinguish between karst and tectonic fractures. In addition, they have applied these criteria within the context of a detailed diagenetic cement history that allows them to further refine the fracture genesis and chronology. In these analyses, the authors evaluated the relationships between fracture intensity, morphologic attributes, host lithology, fracture cement, and oil-staining. From this analysis, they have been able to characterize variations in Ellenburger tectonic fracture intensity by separating these fractures from karst-related features. In general, the majority of fracturing in the Ellenburger is caused by karst-related fracturing although a considerable percentage is caused by tectonism. These findings underscore the importance of considering the complete geologic evolution of a karst reservoir during exploration and field development programs. The authors have been able to more precisely define the spatial significance of the fracture data sets by use of oriented core from Andector Field. They have also demonstrated the importance of these results for exploration and reservoir development programs in West Texas, and the potential to extrapolate these results around the globe. Given the historic interest in the large hydrocarbon reserves in West Texas carbonate reservoirs, results of this study will have tremendous implications for exploration and production strategies targeting vuggy, fractured carbonate systems not only in West Texas, but throughout the globe.
Date: December 31, 1998
Creator: Hoak, T.E.; Sundberg, K.R.; Deyhim, P. & Ortoleva, P.
Partner: UNT Libraries Government Documents Department

Characterization of fracture reservoirs using static and dynamic data: From sonic and 3D seismic to permeability distribution

Description: To characterize the Buena Vista Hills field, the authors have implemented methods of modeling, processing and interpretation. The modeling methods are based on deterministic and stochastic solutions. Deterministic solutions were developed in Phase 1 and applied in Phase 2 to simulate acoustic responses of laminated reservoirs. Specifically, the simulations were aimed at implementing processing techniques to correct P-wave and S-wave velocity logs for scattering effects caused by thin layering. The authors are also including a summary of the theory and the processing steps of this new method for predicting intrinsic dispersion and attenuation in Section 2. Since the objective for correcting velocity scattering effects is to predict intrinsic dispersion from velocity data, they are presenting an application to illustrate how to relate permeability anisotropy with intrinsic dispersion. Also, the theoretical solution for calculating full waveform dipole sonic that was developed in Phase 1 was applied to simulate dipole responses at different azimuthal source orientations. The results will be used to interpret the effects of anisotropy associated with the presence of vertical fractures at Buena Vista Hills. The results of the integration of core, well logs, and geology of Buena Vista Hills is also given in Section 2. The results of this integration will be considered as the input model for the inversion technique for processing production data. Section 3 summarizes accomplishments. In Section 4 the authors present a summary of the technology transfer and promotion efforts associated with this project. In the last section, they address the work to be done in the next six months and future work by applying the processing, modeling and inversion techniques developed in Phases 1 and 2 of this project.
Date: October 1, 1998
Creator: Parra, J.O.; Hackett, C.L.; Brown, R.L.; Collier, H.A. & Datta-Gupta, A.
Partner: UNT Libraries Government Documents Department

A new and superior ultrafine cementitious grout

Description: Sealing fractures in nuclear waste repositories concerns all programs investigating deep burial as a means of disposal. Because the most likely mechanism for contaminant migration is by dissolution and movement through groundwater, sealing programs are seeking low-viscosity sealants that are chemically, mineralogically, and physically compatible with the host rock. This paper presents the results of collaborative work directed by Sandia National Laboratories (SNL) and supported by Whiteshell Laboratories, operated by Atomic Energy of Canada, Ltd. The work was undertaken in support of the Waste Isolation Pilot Plant (WIPP), an underground nuclear waste repository located in a salt formation east of Carlsbad, NM. This effort addresses the technology associated with long-term isolation of nuclear waste in a natural salt medium. The work presented is part of the WIPP plugging and sealing program, specifically the development and optimization of an ultrafine cementitious grout that can be injected to lower excessive, strain-induced hydraulic conductivity in the fractured rock termed the Disturbed Rock Zone (DRZ) surrounding underground excavations. Innovative equipment and procedures employed in the laboratory produced a usable cement-based grout; 90% of the particles were smaller than 8 microns and the average particle size was 4 microns. The process involved simultaneous wet pulverization and mixing. The grout was used for a successful in situ test underground at the WIPP. Injection of grout sealed microfractures as small as 6 microns (and in one rare instance, 3 microns) and lowered the gas transmissivity of the DRZ by up to three orders of magnitude. Following the WIPP test, additional work produced an improved version of the grout containing particles 90% smaller than 5 microns and averaging 2 microns. This grout will be produced in dry form, ready for the mixer.
Date: April 1, 1997
Creator: Ahrens, E.H.
Partner: UNT Libraries Government Documents Department

A comprehensive study of fracture patterns and densities in the Geysers geothermal reservoir using microearthquake shear-wave splitting tomography. [Quarterly progress report 03/16/1998 - 06/15/1998]

Description: We completed the process of identifying shear-wave splitting in the Geyser area. A total of 2700 observations were recorded with about 1700 observations from the 1988 data and about 1000 observations from 1994. Fast polarization direction map in Figure 1 shows that most of the stations in the Geyser area display consistent direction throughout the main field, between 0{degree} azimuth to 40{degree} azimuth. Some exemptions to the consistent crack alignment (fast polarization direction) can be seen in stations 9 and station 3, and also in stations 13 and 14 outside the field. Since the stations are in boreholes it is possible that some of the station orientations, calculated using P-wave arrivals from located events, are erroneous. If we treat measurements of polarization direction as a statistical process, same as deep of layer measurement, we can say that in the small area of the station we have aligned cracks. Figures 2 and 3 show results of the crack density inversion assuming regional crack azimuth of 20{degree}. Almost 2400 raypaths were used to perform this tomographic inversion. There is weak dependency of the results on the regional crack direction, but the main areas of high and low crack density are the same. The changes are mainly in the size of the anomalies. Since the amplitudes of those anomalies depend mainly on the damping parameter we use in the inversion, exact regional crack direction is not a critical parameter of the inversion. The map in figure 2 and cross-sections in Figure 3 show two areas of high crack density at the top 1 km one at station 8 and the other between stations 6 and 5. At greater depth of 1 to 2 km those two area converge to one high crack density anomaly between stations 3, 4, 11, and 10.
Date: March 17, 1999
Creator: Malin, P.E. & Shalev, E.
Partner: UNT Libraries Government Documents Department

A comprehensive study of fracture patterns and densities in the Geysers geothermal reservoir using microearthquake shear-wave splitting tomography [Quarterly progress report 06/16/1998 - 09/15/1998]

Description: We completed the process of locating events and identifying shear-wave splitting in the mammoth area. A total of 2250 split shear wave observations were recorded in the four month period that our network was in place. Fast polarization direction map in Figure 1 shows that most of the stations in the mammoth area display consistent direction throughout the main field, between 300{degree} azimuth to 0{degree} azimuth. Some exemptions to the consistent crack alignment (fast polarization direction) can be seen in station M19, and some stations display inconsistent trend as can be observed in stations M25, M18, and M07. It is possible that station M19 was misaligned during installment. Figure 2 shows the cumulative rose diagram for all observations with a clear preferred direction. Figure 3 also shows that most of the observations of fast split shear wave are in the same direction and that those observation are distributed throughout the target area. If we treat measurements of polarization direction as a statistical process, same as deep of layer measurement, we can say that in the small area of the station we have aligned cracks. Figures 4 and 5 show results of the crack density inversion assuming regional crack azimuth of 340{degree}. Almost 2000 raypaths were used to perform this tomographic inversion. There is weak dependency of the results on the regional crack direction, but the main areas of high and low crack density are the same. The changes are mainly in the size of the anomalies. Since the amplitudes of those anomalies depend mainly on the damping parameter we use in the inversion, exact regional crack direction is not a critical parameter of the inversion. The map in figure 4 and cross-sections in Figure 5 show two areas of high crack density: one northeast of the Casa Diablo area at ...
Date: March 26, 1999
Creator: Malin, P.E. & Shalev, E.
Partner: UNT Libraries Government Documents Department

Analecta of structures formed during the 28 June 1992 Landers-Big Bear, California earthquake sequence (including maps of shear zones, belts of shear zones, tectonic ridge, duplex en echelon fault, fault elements, and thrusts in restraining steps)

Description: The June 28, 1992, M{sub s} 7.5 earthquake at Landers, California, which occurred about 10 km north of the community of Yucca Valley, California, produced spectacular ground rupturing more than 80 km in length (Hough and others, 1993). The ground rupturing, which was dominated by right-lateral shearing, extended along at least four distinct faults arranged broadly en echelon. The faults were connected through wide transfer zones by stepovers, consisting of right-lateral fault zones and tension cracks. The Landers earthquakes occurred in the desert of southeastern California, where details of ruptures were well preserved, and patterns of rupturing were generally unaffected by urbanization. The structures were varied and well-displayed and, because the differential displacements were so large, spectacular. The scarcity of vegetation, the aridity of the area, the compactness of the alluvium and bedrock, and the relative isotropy and brittleness of surficial materials collaborated to provide a marvelous visual record of the character of the deformation zones. The authors present a series of analecta -- that is, verbal clips or snippets -- dealing with a variety of structures, including belts of shear zones, segmentation of ruptures, rotating fault block, en echelon fault zones, releasing duplex structures, spines, and ramps. All of these structures are documented with detailed maps in text figures or in plates (in pocket). The purpose is to describe the structures and to present an understanding of the mechanics of their formation. Hence, most descriptions focus on structures where the authors have information on differential displacements as well as spatial data on the position and orientation of fractures.
Date: December 31, 1997
Creator: Johnson, A.M.; Johnson, N.A.; Johnson, K.M.; Wei, W.; Fleming, R.W.; Cruikshank, K.M. et al.
Partner: UNT Libraries Government Documents Department

Calculation of discrete fracture flow paths in dual-continuum models

Description: Movement of water through fractures plays an important role in performance assessments of the potential high-level nuclear waste repository at Yucca Mountain, Nevada. The magnitude and frequency of water flowing through individual fractures impacts predictions of the near-field environment and waste-package corrosion. Discrete fracture flow paths, referred to as ``weeps``, have been derived from dual continuum models of fracture flow. The required parameters include the geometric fracture spacing, an assumed width of each weep, and a scaling factor that accounts for reduced flow between fracture and matrix elements in dual continuum models. The formulation provides a convenient means to determine discrete weep spacing and flow rates that are mathematically consistent with the dual continuum model. Specific applications and examples related to seepage into drifts are also discussed.
Date: December 1, 1997
Creator: Ho, C.K. & Wilson, M.L.
Partner: UNT Libraries Government Documents Department

Discriminating effects of heterogeneity and matrix diffusion by alternative tracer designs

Description: Flow and transport calculations are carried out by numerical simulation for different tracer designs: single-well radially diverging/converging (huff-puff), single well radially converging, and two-well injection-withdrawal (doublet) in a 2D fracture zone. The fractured rocks are conceptualized as a dual-continuum: the well-connected fractures forming a heterogeneous continuum for advective transport, and the less permeable matrix forming a second continuum for tracer diffusion. Results show that the huff-puff design can be a good diagnostic test for matrix diffusion. The two-well doublet design averages over a large volume and corrects for the extreme sensitivity to spatial heterogeneities of the single well converging test, but requires prior knowledge of presence or absence of matrix diffusion to give reliable estimate of transport parameters. Results of this study demonstrate that using a suite of different tracer designs is important to reduce the uncertainty in association with solving the inverse problem of tracer test interpretation to characterize transport in fractured rocks.
Date: March 1, 1995
Creator: Tsang, Y.Y.W.
Partner: UNT Libraries Government Documents Department

Discrete Feature Approach for Heterogeneous Reservoir Production Enhancement

Description: This progress report describes activities during the period January 1, 1999 to June 30, 1999. Work was carried out on 21 tasks. The major activity during the reporting period was the development and preliminary application of discrete fracture network (DFN) models for Stoney Point, South Oregon Basin, and North Oregon Basins project study sites. In addition, research was carried out on analysis algorithms for discrete future orientation.
Date: September 6, 2001
Creator: Dershowitz, William S. & Cladouhos, Trenton
Partner: UNT Libraries Government Documents Department

Tectonic Setting and Characteristics of Natural Fractures in MesaVerde and Dakota Reservoirs of the San Juan Basin

Description: The Cretaceous strata that fill the San Juan Basin of northwestern New Mexico and southwestern Colorado were shortened in a generally N-S to NN13-SSW direction during the Laramide orogeny. This shortening was the result of compression of the strata between southward indentation of the San Juan Uplift at the north edge of the basin and northward to northeastward indentation of the Zuni Uplift from the south. Right-lateral strike-slip motion was concentrated at the eastern and western basin margins of the basin to form the Hogback Monocline and the Nacimiento Uplift at the same time, and small amounts of shear may have been pervasive within the basin as well. Vertical extension fractures, striking N-S to NNE-SSW with local variations (parallel to the Laramide maximum horizontal compressive stress), formed in both Mesaverde and Dakota sandstones under this system, and are found in outcrops and in the subsurface of the San Juan Basin. The immature Mesaverde sandstones typically contain relatively long, irregular, vertical extension fractures, whereas the quartzitic Dakota sandstones contain more numerous, shorter, sub-parallel, closely spaced, extension fractures. Conjugate shear planes in several orientations are also present locally in the Dakota strata.
Date: December 20, 2000
Creator: Lorenz, John C. & Cooper, Scott P.
Partner: UNT Libraries Government Documents Department