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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

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

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

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

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

Studies of injection into naturally fractured reservoirs

Description: A semi-analytical model for studies of cold water injectioninto naturally fractured reservoirs has been developed. The model can beused to design the flow rates and location of injection wells in suchsystems. The results obtained using the model show that initially thecold water will move very rapidly through the fracture system away fromthe well. Later on, conductive heat transfer from the rock matrix blockswill retard the advancement of the cold water front, and eventuallyuniform energy sweep conditions will prevail. Where uniform energy sweepconditions are reached the cold waer movement away from the injectionwell will be identical to that in a porous medium; consequently maximumenergy recovery from the rock matrix will be attained. The time ofuniform energy sweep and the radial distance from the injection wellwhere it occurs are greatly dependent upon the fracture spacing, butindependent of the fracture aperture.
Date: July 1, 1982
Creator: Bodvarsson, Gudmundur S. & Lai, Cheng Hsien
Partner: UNT Libraries Government Documents Department

An integrated methodology for characterizing flow and transportprocesses in fractured rock

Description: To investigate the coupled processes involved in fluid andheat flow and chemical transport in the highly heterogeneous,unsaturated-zone (UZ) fractured rock of Yucca Mountain, we present anintegrated modeling methodology. This approach integrates a wide varietyof moisture, pneumatic, thermal, and geochemical isotopic field data intoa comprehensive three-dimensional numerical model for modeling analyses.The results of field applications of the methodology show that moisturedata, such as water potential and liquid saturation, are not sufficientto determine in situ percolation flux, whereas temperature andgeochemical isotopic data provide better constraints to net infiltrationrates and flow patterns. In addition, pneumatic data are found to beextremely valuable in estimating large-scale fracture permeability. Theintegration of hydrologic, pneumatic, temperature, and geochemical datainto modeling analyses is thereby demonstrated to provide a practicalmodeling approachfor characterizing flow and transport processes incomplex fractured formations.
Date: August 31, 2007
Creator: Wu, Yu-Shu
Partner: UNT Libraries Government Documents Department

Tracer Recovery and Mixing from Two Geothermal Injection-Backflow Studies

Description: Injection-backflow tracer testing on a single well is not a commonly used procedure for geothermal reservoir evaluation, and, consequently, there is little published information on the character or interpretation of tracer recovery curves. Two field experiments were conducted to develop chemical tracer procedures for use with injection-backflow testing, one on the fracture-permeability Raft River reservoir and the other on the matrix-permeability East Mesa reservoir. Results from tests conducted with incremental increases in the injection volume at both East Mesa and Raft River suggests that, for both reservoirs, permeability remained uniform with increasing distance from the well bore. Increased mixing during quiescent periods, between injection and backflow, at Raft River suggest an area near the well bore that has a hydrologic character different from the far well bore environment. Increased flow rates for East Mesa testing resulted in a general decrease in mixing. Comparison of recovery curves from the Raft River reservoir with those from the East Mesa reservoir suggests that mixing is greatest, and therefore permeability is greatest, in the fractured reservoir. These test results indicate that injection-backflow testing with tracers can be used successfully to characterize flow in the near-well bore environment.
Date: December 15, 1983
Creator: Capuano, R.M.; Adams, M.C. & Wright, P.M.
Partner: UNT Libraries Government Documents Department

Italian Experience and Problems in Deep Geothermal Drilling

Description: Geothermal exploration at depth is being conducted in the Larderello area of Italy, in order to ascertain whether it is possible to extract geothermal fluids from the layers which underlie the reservoir now being exploited. The main operating problems are caused by the high thermality and the chemical corrosiveness of the fluids encountered; and by the practical problems involved in drilling without circulation to the surface in mainly hard but anhomogeneous fractured formations. The technology employed for deep geothermal well drilling plays an important role in this research. In deep geothermal well drilling it is essential that the equipment and the materials employed are suitable for use in areas which are characterized by high thermality and chemical corrosiveness. The results of the experiences gained in Italy concerning the materials and tools employed in deep geothermal exploration are presented. The various problems involved are described in detail and particular mention is made of drift control, fishing operations, cementation of the deep casing, control of the circulation fluid, and choice of the tubular materials.
Date: January 1, 1981
Creator: Cigni, U.; Del Gaudio, P. & Fabbri, F.
Partner: UNT Libraries Government Documents Department

An investigation of radial tracer flow in naturally fractured reservoirs

Description: This study presents a general solution for the radial flow of tracers in naturally fractured reservoirs. Continuous and finite step injection of chemical and radioactive tracers are considered. The reservoir is treated as being composed of two regions: a mobile region where longitudinal dispersion and convection take place and a stagnant region where only diffusion and adsorption are allowed. Radioactive decay is considered in both regions. The model of this study is thoroughly compared to those previously presented in literature by Moench and Ogata, Tang et al., Chen et al., and Hsieh et al. The solution is numerically inverted by means of the Crump algorithm. A detailed validation of the model with respect to solutions previously presented and/or simplified physical conditions solutions (i.e., homogeneous case) or limit solutions (i.e., for short times) was carried out. The influence of various dimensionless parameters that enter into the solution was investigated. A discussion of results obtained through the Crump and Stehfest algorithm is presented, concluding that the Crump method provides more reliable tracer concentrations.
Date: January 1, 1991
Creator: Jetzabeth, Ramirez-Sabag; Fernando, Samaniego V.; Jesus, Rivera R. & Rodriguez, Fernando
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

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

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 partitioning interwell tracer tests in hydrocarbon reservoirs. Specifically, we utilize the unique features of streamline models to develop an efficient approach for interpretation and history matching of field tracer response. A critical aspect here is the underdetermined and highly ill-posed nature of the associated inverse problems. We have investigated the relative merits of the traditional history matching ('amplitude inversion') and a novel travel time inversion in terms of robustness of the method and convergence behavior of the solution. We show that the traditional amplitude inversion is orders of magnitude more non-linear and the solution here is likely to get trapped in local minimum, leading to inadequate history match. The proposed travel time inversion is shown to be extremely efficient and robust for practical field applications. The streamline approach is generalized to model water injection in naturally fractured reservoirs through the use of a dual media approach. The fractures and matrix are treated as separate continua that are connected through a transfer function, as in conventional finite difference simulators for modeling fractured systems. A detailed comparison with a commercial finite difference simulator shows very good agreement. Furthermore, an examination of the scaling behavior of the computation time indicates that the streamline approach is likely to result in significant savings for large-scale field applications. We also propose a novel approach to history matching finite-difference models that combines the advantage of the streamline models with the versatility of finite-difference simulation. In our approach, we utilize the streamline-derived sensitivities to facilitate history matching during finite-difference simulation. The use of finite-difference model allows us to account for detailed process physics and compressibility effects. The approach is very fast and avoids much of the subjective judgments and time-consuming trial-and-errors associated with manual history matching. We ...
Date: December 31, 2006
Creator: Datta-Gupta, Akhil
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 felt confident that funds could be acquired by third quarter 2005 at which time it would have been necessary to request a project extension to complete the originally designed study. A project extension was granted but it appears Goldrus will have difficulty securing funds. We Bureau of Economic Geology are investigating a new approach on how to fulfill our initial objectives of promoting high-pressure air injection of Ellenburger reservoirs.
Date: February 1, 2006
Creator: Loucks, Robert & Ruppel, Stephen C.
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

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

Upscaling solute transport in naturally fractured porous media with the continuous time random walk method

Description: Solute transport in fractured porous media is typically 'non-Fickian'; that is, it is characterized by early breakthrough and long tailing and by nonlinear growth of the Green function-centered second moment. This behavior is due to the effects of (1) multirate diffusion occurring between the highly permeable fracture network and the low-permeability rock matrix, (2) a wide range of advection rates in the fractures and, possibly, the matrix as well, and (3) a range of path lengths. As a consequence, prediction of solute transport processes at the macroscale represents a formidable challenge. Classical dual-porosity (or mobile-immobile) approaches in conjunction with an advection-dispersion equation and macroscopic dispersivity commonly fail to predict breakthrough of fractured porous media accurately. It was recently demonstrated that the continuous time random walk (CTRW) method can be used as a generalized upscaling approach. Here we extend this work and use results from high-resolution finite element-finite volume-based simulations of solute transport in an outcrop analogue of a naturally fractured reservoir to calibrate the CTRW method by extracting a distribution of retention times. This procedure allows us to predict breakthrough at other model locations accurately and to gain significant insight into the nature of the fracture-matrix interaction in naturally fractured porous reservoirs with geologically realistic fracture geometries.
Date: April 1, 2010
Creator: Geiger, S.; Cortis, A. & Birkholzer, J.T.
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

A Physically Based Approach for Modeling Multiphase Fracture-Matrix Interaction in Fractured Porous Media

Description: Modeling fracture-matrix interaction within a complex multiple phase flow system is a key issue for fractured reservoir simulation. Commonly used mathematical models for dealing with such interactions employ a dual- or multiple-continuum concept, 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, in which the fracture relative permeability is used to represent the counterpart at the fracture-matrix interface, is the most common scheme by which to estimate flow mobility for fracture-matrix flow terms. However, such a scheme has a serious flaw, which may lead to unphysical solutions or significant numerical errors. To overcome the limitation 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 models.
Date: March 15, 2004
Creator: Wu, Yu-Shu; Pan, Lehua & Pruess, Karsten
Partner: UNT Libraries Government Documents Department

DILUTE SURFACTANT METHODS FOR CARBONATE FORMATIONS

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. We have acquired field oil and core samples and field brine compositions from Marathon. We have conducted preliminary adsorption and wettability studies. Addition of Na{sub 2}CO{sub 3} decreases anionic surfactant adsorption on calcite surface. Receding contact angles increase with surfactant adsorption. Plans for the next quarter include conducting adsorption, phase behavior and wettability studies.
Date: January 1, 2003
Creator: Mohanty, Kishore K.
Partner: UNT Libraries Government Documents Department

An example of using oil-production induced microseismicity in characterizing a naturally fractured reservoir

Description: Microseismic monitoring was conducted using downhole geophone tools deployed in the Seventy-Six oil field, Clinton County, Kentucky. Over a 7-month monitoring period, 3237 microearthquakes were detected during primary oil production; no injection operations were conducted. Gross changes in production rate correlate with microearthquake event rate with event rate lagging production-rate changes by about 2 weeks. Hypocenters and first-motion data have revealed low-angle, thrust fracture zones above and below the currently drained depth interval. Production history, well logs and drill tests indicate the seismically-active fractures are previously drained intervals that have subsequently recovered to hydrostatic pressure via brine invasion. The microseismic data have revealed, for the first time, the importance of the low-angle fractures in the storage and production of oil in the study area. The seismic behavior is consistent with poroelastic models that predict slight increases in compressive stress above and below currently drained volumes.
Date: June 1, 1996
Creator: Rutledge, J.T.; Phillips, W.S.; Schuessler, B.K. & Anderson, D.W.
Partner: UNT Libraries Government Documents Department