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A physically based numerical approach for modeling fracture-matrix interaction in fractured reservoirs

Description: Modeling fracture-matrix interaction within a multiple-phase flow system is a key issue for fractured reservoir simulation. Commonly used mathematical models for dealing with such interactions employ dual- or multiple-continuum concepts, in which fractures and matrix are represented as overlapping, different, but interconnected continua, described by parallel sets of conservation equations. The conventional single-point upstream weighting scheme is most commonly used to estimate flow mobility for fracture-matrix flow. However, such a scheme may have serious limitations or flaws, which lead to unphysical solutions or significant numerical errors. To overcome the limitations of the conventional upstream weighting scheme, this paper presents a physically based modeling approach for estimating physically correct relative permeability in calculating multiphase flow between fractures and the matrix, using continuity of capillary pressure at the fracture-matrix interface. The proposed approach has been implemented into two multiphase reservoir simulators and verified using analytical solutions and laboratory experimental data. The new method is demonstrated to be accurate, numerically efficient, and easy to implement in dual- or multiple-continuum reservoir simulators.
Date: May 4, 2004
Creator: Wu, Yu-Shu & Pruess, Karsten
Partner: UNT Libraries Government Documents Department

Development of Reservoir Characterization Techniques and Production Models for Exploiting Naturally Fractured Reservoirs

Description: This report focuses on integrating geoscience and engineering data to develop a consistent characterization of the naturally fractured reservoirs. During this reporting period, effort was focused on relating seismic data to reservoir properties of naturally fractured reservoirs, scaling well log data to generate interwell descriptors of these reservoirs, enhancing and debugging a naturally fractured reservoir simulator, and developing a horizontal wellbore model for use in the simulator.
Date: March 28, 2001
Creator: Wiggins, M.L.; Evans, R.D.; Brown, R.L. & Gupta, A.
Partner: UNT Libraries Government Documents Department

Advanced Characterization of Fractured Reservoirs in Carbonate Rocks: The Michigan Basin

Description: The main objective of this project is for a university-industry consortium to develop a comprehensive model for fracture carbonate reservoirs based on the ''data cube'' concept using the Michigan Basin as a prototype. This project combined traditional historical data with 2D and 3D seismic data as well as data from modern logging tools in a novel way to produce a new methodology for characterizing fractured reservoirs in carbonate rocks. Advanced visualization software was used to fuse the data and to image it on a variety of scales, ranging from basin-scale to well-scales.
Date: October 24, 2000
Creator: Wood, James R. & Harrison, William B.
Partner: UNT Libraries Government Documents Department

Aligned vertical fractures, HTI reservoir symmetry, and Thomsenseismic anisotropy parameters

Description: The Sayers and Kachanov (1991) crack-influence parametersare shown to be directly related to Thomsen (1986) weak-anisotropyseismic parameters for fractured reservoirs when the crack density issmall enough. These results are then applied to seismic wave propagationin reservoirs having HTI symmetry due to aligned vertical fractures. Theapproach suggests a method of inverting for fracture density from wavespeed data.
Date: June 27, 2007
Creator: Berryman, James G.
Partner: UNT Libraries Government Documents Department

Coupled thermohydromechanical analysis of a heater test in unsaturated clay and fractured rock at Kamaishi Mine

Description: The recent interest in coupled thermohydromechanical (THM) processes associated with geological disposal of spent nuclear fuel, and in particular the issue of resaturation of a clay buffer around a waster canister, has encouraged major development of the finite element computer program ROCMAS in the past three years. The main objective is to develop a tool for analysis of THM processes in practical field scale, including fractured rock masses and detailed behavior of the near-field, nonisothermal and unsaturated system composed of rock fractures and clay buffer. In this report, the ROCMAS code is presented and applied for modeling of coupled THM processes in small laboratory samples of bentonite clay as well as a larg in situ THM experiment in fractured rocks, at Kamaishi Mine, Japan.
Date: August 1, 1999
Creator: Rutqvist, Jonny; Noorishad, Jahan & Tsang, Chin-Fu
Partner: UNT Libraries Government Documents Department

Investigation of Efficiency Improvements During CO2 Injection in Hydraulically and Naturally Fractured Reservoirs

Description: The objective of this project was to perform unique laboratory experiments with artificial fractured cores (AFCs) and X-ray CT to examine the physical mechanisms of bypassing in HFR and NFR that eventually result in less efficient CO2 flooding in heterogeneous or fracture-dominated reservoirs. This report provided results of the second semi-annual technical progress report that consists of three different topics.
Date: March 10, 2003
Creator: Schechter, David S. & Vance, Harold
Partner: UNT Libraries Government Documents Department

Experimental and Analytical Study of Multidimensional Imbibition in Fractured Porous Media, SUPRI TR-129

Description: Using an X-ray computerized tomography (CT) scanner, and a novel, CT-compatible core holder, performed a series of experiments to study air and oil expulsion from rock samples by capillary imbibition of water in a three-dimensional geometry. The air-water system was useful in that a relatively large number of experiments can be conducted to delineate physical processes. Different injection rates and fracture apertures were utilized. Two different fracture flow regimes were identified. The ''filling-fracture'' regime shows a plane source that grows in length due to relatively slow water flow through fractures. In the second, ''instantly-filled fracture'' regime, the time to fill the fracture is much less than the imbibition time. Here, imbibition performance scales as the square root of time. In the former regime, the mass of water imbibed scales linearly with time.
Date: April 24, 2002
Creator: Rangel-German, E.R. & Kovscek, A.R.
Partner: UNT Libraries Government Documents Department

HOW DUAL-SCALE DIFFUSIVE PROPERTY HETEROGENEITY AFFECTS EFFECTIVE MATRIX DIFFUSION COEFFICIENT IN FRACTURED ROCK

Description: Matrix diffusion can significantly retard solute transport in fractured formations. Understanding matrix diffusion is crucial for predicting the arrival time, peak concentration, and tail of a contaminant breakthrough curve. Previous studies show that the effective matrix diffusion coefficient may be scale dependent. This study examines how heterogeneities of diffusion properties affect the effective matrix diffusion coefficient. Two types of heterogeneity in a channelized flow system are considered in the study: (1) interchannel heterogeneity, and (2) intrachannel heterogeneity. The objectives of this study are (1) to examine if it is appropriate to use a single, effective matrix diffusion coefficient in a standard solution model to predict breakthrough curves (BTC) in a fractured formation, (2) if so, how this effective value is related to the degree of the matrix diffusion coefficient variability; and (3) to examine if the observed scale dependence of the effective matrix-diffusion coefficient is caused by heterogeneity in diffusion properties. The results show that the use of a single effective matrix diffusion coefficient is appropriate only if the inter- and intrachannel variability of diffusion properties is small. The scale dependence of the effective matrix diffusion coefficient is not caused by either type of the studied heterogeneity.
Date: September 7, 2005
Creator: Zhang, Y.; Liu, H.; Zhou, Q. & Finsterle, S.
Partner: UNT Libraries Government Documents Department

Research program on fractured petroleum reservoirs. [Quarterly report], October 1--December 31, 1995

Description: A number of experiments have been performed to study water injection in fractured porous media. These experiments reveal that: (1) the co-current imbibition may be the primary flow process in water-wet fractured media, and (2) the imbibition may result in over 20 percent recovery from very tight rock (Austin Chalk with K{sub ma} of the order of 0.01 md) for an imbibition period of about 2 months. Theoretical consideration reveal that the exponential function of Aronofsky et al. [``A Model for the Mechanism of Oil Recovery from Porous Matrix Due to Water Invasion In Fractured Reservoirs,`` Trans. AIME (1958) 213, 17-19] does not describe the early-time, but may represent the late-time recovery.
Date: January 31, 1996
Creator: Firoozabadi, A.
Partner: UNT Libraries Government Documents Department

Fractured petroleum reservoirs

Description: Total compressibility in a fractured reservoir is estimated using the pressure response due to gravitational potential variations. Both the moon and the sun gravitational potentials are accounted for using the full expression by inclusion of longer-period components. The semi-diurnal and diurnal pressure data show substantial long-term variations. The gravitational potential also contains the same variation trend; the ratio between the potential and pressure has a fairly uniform value over successive cycles. The computed total compressibility is also fairly constant and independent of the cycle. Results show the effects of the time interval over which the pressure measurements are performed as well as the location.
Date: January 10, 2000
Creator: Firoozabadi, A.; Chang, E. & Tang, G.Q.
Partner: UNT Libraries Government Documents Department

Numerical simulation of single-phase and multiphase non-Darcy flowin porous and fractured reservoirs

Description: A numerical method as well as a theoretical study of non-Darcy fluid flow of through porous and fractured reservoirs is described. The non-Darcy flow is handled in a three-dimensional, multiphase flow reservoir simulator, while the model formulation incorporates the Forchheimer equation for describing single-phase or multiphase non-Darcy flow and displacement. The numerical scheme has been verified by comparing its results against those of analytical methods. Numerical solutions are used to obtain some insight into the physics of non-Darcy flow and displacement in reservoirs. In addition, several type curves are provided for well-test analyses of non-Darcy flow to demonstrate a methodology for modeling this type of flow in porous and fractured rocks, including flow in geothermal reservoirs.
Date: June 2, 2000
Creator: Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department

Development of Reservoir Characterization Techniques and Production Models for Exploiting Naturally Fractured Reservoirs

Description: This research was directed toward developing a systematic reservoir characterization methodology which can be used by the petroleum industry to implement infill drilling programs and/or enhanced oil recovery projects in naturally fractured reservoir systems in an environmentally safe and cost effective manner. It was anticipated that the results of this research program will provide geoscientists and engineers with a systematic procedure for properly characterizing a fractured reservoir system and a reservoir/horizontal wellbore simulator model which can be used to select well locations and an effective EOR process to optimize the recovery of the oil and gas reserves from such complex reservoir systems.
Date: February 11, 2003
Creator: Wiggins, Michael L.; Brown, Raymon L.; Civan, Faruk & Hughes, Richard G.
Partner: UNT Libraries Government Documents Department

Effects of non-condensible gases on fluid recovery in fracturedgeothermal reservoirs

Description: Numerical simulations are performed in order to investigate the effects of noncondensible gases, (CO{sub 2}) on fluid recovery and matrix depletion in fractured geothermal reservoirs. The model used is that of a well producing at a constant bottomhole pressure from a two-phase fractured reservoir. The results obtained have revealed a complex fracture-matrix interaction due to the thermodynamics of H{sub 2}O-CO{sub 2} mixtures. Although the matrix initially contributes fluids (liquid and gas) to the fractures, later on, the flow directions reverse and the fractures backflow fluids into the matrix. The amount of backflow depends primarily upon the flowing gas saturation in the fractures; the lower the flowing gas saturation in the fractures the more backflow. It is shown that the recoverable fluid reserves depend strongly on the amount of CO{sub 2} present in the reservoir system.
Date: January 1, 1986
Creator: Bodvarsson, Gudmundur S. & Gaulke, Scott
Partner: UNT Libraries Government Documents Department

Reviving Abandoned Reservoirs with High-Pressure Air Injection: Application in a Fractured and Karsted Dolomite Reservoir

Description: The field operator, Goldrus Producing Company, has been unable to secure funding needed to continue the field demonstration phase of the project. Accordingly, we have temporarily halted all project activities until necessary funding is obtained. Goldrus is confident that funds can be acquired by third quarter 2005 at which time it will be necessary to request a project extension to complete the originally designed study.
Date: March 31, 2005
Creator: Loucks, Robert & Ruppel, Stephen C.
Partner: UNT Libraries Government Documents Department

Modeling Wettability Alteration using Chemical EOR Processes in Naturally Fractured Reservoirs

Description: The objective of our search is to develop a mechanistic simulation tool by adapting UTCHEM to model the wettability alteration in both conventional and naturally fractured reservoirs. This will be a unique simulator that can model surfactant floods in naturally fractured reservoir with coupling of wettability effects on relative permeabilities, capillary pressure, and capillary desaturation curves. The capability of wettability alteration will help us and others to better understand and predict the oil recovery mechanisms as a function of wettability in naturally fractured reservoirs. The lack of a reliable simulator for wettability alteration means that either the concept that has already been proven to be effective in the laboratory scale may never be applied commercially to increase oil production or the process must be tested in the field by trial and error and at large expense in time and money. The objective of Task 1 is to perform a literature survey to compile published data on relative permeability, capillary pressure, dispersion, interfacial tension, and capillary desaturation curve as a function of wettability to aid in the development of petrophysical property models as a function of wettability. The new models and correlations will be tested against published data. The models will then be implemented in the compositional chemical flooding reservoir simulator, UTCHEM. The objective of Task 2 is to understand the mechanisms and develop a correlation for the degree of wettability alteration based on published data. The objective of Task 3 is to validate the models and implementation against published data and to perform 3-D field-scale simulations to evaluate the impact of uncertainties in the fracture and matrix properties on surfactant alkaline and hot water floods.
Date: September 30, 2007
Creator: Delshad, Mojdeh; Pope, Gary A. & Sepehrnoori, Kamy
Partner: UNT Libraries Government Documents Department

Inversion of multicomponent seismic data and rock-physics intepretation for evaluating lithology, fracture and fluid distribution in heterogeneous anisotropic reservoirs

Description: Within the framework of this collaborative project with the Lawrence Livermore National Laboratory (LLNL) and Stanford University, the Colorado School of Mines (CSM) group developed and implemented a new efficient approach to the inversion and processing of multicomponent, multiazimuth seismic data in anisotropic media. To avoid serious difficulties in the processing of mode-converted (PS) waves, we devised a methodology for transforming recorded PP- and PS-wavefields into the corresponding SS-wave reflection data that can be processed by velocity-analysis algorithms designed for pure (unconverted) modes. It should be emphasized that this procedure does not require knowledge of the velocity model and can be applied to data from arbitrarily anisotropic, heterogeneous media. The azimuthally varying reflection moveouts of the PP-waves and constructed SS-waves are then combined in anisotropic stacking-velocity tomography to estimate the velocity field in the depth domain. As illustrated by the case studies discussed in the report, migration of the multicomponent data with the obtained anisotropic velocity model yields a crisp image of the reservoir that is vastly superior to that produced by conventional methods. The scope of this research essentially amounts to building the foundation of 3D multicomponent, anisotropic seismology. We have also worked with the LLNL and Stanford groups on relating the anisotropic parameters obtained from seismic data to stress, lithology, and fluid distribution using a generalized theoretical treatment of fractured, poroelastic rocks.
Date: November 17, 2004
Creator: Tsvankin, Ilya & Larner, Kenneth L.
Partner: UNT Libraries Government Documents Department

Dilute Surfactant Methods for Carbonate Formations Quarterly Report

Description: There are many carbonate reservoirs in US (and the world) with light oil and fracture pressure below its minimum miscibility pressure (or reservoir may be naturally fractured). Many carbonate reservoirs are naturally fractured. Waterflooding is effective in fractured reservoirs, if the formation is water-wet. Many fractured carbonate reservoirs, however, are mixed-wet and recoveries with conventional methods are low (less than 10%). Thermal and miscible tertiary recovery techniques are not effective in these reservoirs. Surfactant flooding (or huff-n-puff) is the only hope, yet it was developed for sandstone reservoirs in the past. The goal of this research is to evaluate dilute (hence relatively inexpensive) surfactant methods for carbonate formations and identify conditions under which they can be effective. Laboratory imbibition tests show about 61% oil recovery in the case of Alf-38 and 37% in the case of DTAB. A numerical model has been developed that fits the rate of imbibition of the laboratory experiment. Field-scale fracture block simulation shows that as the fracture spacing increases, so does the time of recovery. Plans for the next quarter include simulation studies.
Date: April 1, 2005
Creator: Mohanty, Kishore K.
Partner: UNT Libraries Government Documents Department

Interpreting Fracture Patterns in Sandstones Interbedded with Ductile Strata at the Salt Valley Anticline, Arches National Park, Utah

Description: Sandstones that overlie or that are interbedded with evaporitic or other ductile strata commonly contain numerous localized domains of fractures, each covering an area of a few square miles. Fractures within the Entrada Sandstone at the Salt Valley Anticline are associated with salt mobility within the underlying Paradox Formation. The fracture relationships observed at Salt Valley (along with examples from Paleozoic strata at the southern edge of the Holbrook basin in northeastern Arizona, and sandstones of the Frontier Formation along the western edge of the Green River basin in southwestern Wyoming), show that although each fracture domain may contain consistently oriented fractures, the orientations and patterns of the fractures vary considerably from domain to domain. Most of the fracture patterns in the brittle sandstones are related to local stresses created by subtle, irregular flexures resulting from mobility of the associated, interbedded ductile strata (halite or shale). Sequential episodes of evaporite dissolution and/or mobility in different directions can result in multiple, superimposed fracture sets in the associated sandstones. Multiple sets of superimposed fractures create reservoir-quality fracture interconnectivity within restricted localities of a formation. However, it is difficult to predict the orientations and characteristics of this type of fracturing in the subsurface. This is primarily because the orientations and characteristics of these fractures typically have little relationship to the regional tectonic stresses that might be used to predict fracture characteristics prior to drilling. Nevertheless, the high probability of numerous, intersecting fractures in such settings attests to the importance of determining fracture orientations in these types of fractured reservoirs.
Date: December 1, 2001
Creator: LORENZ, JOHN C. & COOPER, SCOTT P.
Partner: UNT Libraries Government Documents Department

An Integrated Approach to Characterizing Bypassed Oil in Heterogeneous and Fractured Reservoirs Using Partitioning Tracers

Description: We explore the use of efficient streamline-based simulation approaches for modeling and analysis partitioning interwell tracer tests in heterogeneous and fractured hydrocarbon reservoirs. We compare the streamline-based history matching techniques developed during the first two years of the project with the industry standard assisted history matching. We enhance the widely used assisted history matching in two important aspects that can significantly improve its efficiency and effectiveness. First, we utilize streamline-derived analytic sensitivities to relate the changes in reservoir properties to the production response. These sensitivities can be computed analytically and contain much more information than that used in the assisted history matching. Second, we utilize the sensitivities in an optimization procedure to determine the spatial distribution and magnitude of the changes in reservoir parameters needed to improve the history-match. By intervening at each iteration during the optimization process, we can retain control over the history matching process as in assisted history matching. This allows us to accept, reject, or modify changes during the automatic history matching process. We demonstrate the power of our method using two field examples with model sizes ranging from 10{sup 5} to 10{sup 6} grid blocks and with over one hundred wells. We have also extended the streamline-based production data integration technique to naturally fractured reservoirs using the dual porosity approach. The principal features of our method are the extension of streamline-derived analytic sensitivities to account for matrix-fracture interactions and the use of our previously proposed generalized travel time inversion for history matching. Our proposed workflow has been demonstrated by using both a dual porosity streamline simulator and a commercial finite difference simulator. Our approach is computationally efficient and well suited for large scale field applications in naturally fractured reservoirs with changing field conditions. This considerably broadens the applicability of the streamline-based analysis of tracer data …
Date: August 1, 2005
Creator: Datta-Gupta, Akhil
Partner: UNT Libraries Government Documents Department
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