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Analytic crack solutions for tilt fields around hydraulic fractures

Description: The recent development of downhole tiltmeter arrays for monitoring hydraulic fractures has provided new information on fracture growth and geometry. These downhole arrays offer the significant advantages of being close to the fracture (large signal) and being unaffected by the free surface. As with surface tiltmeter data, analysis of these measurements requires the inversion of a crack or dislocation model. To supplement the dislocation models of Davis [1983], Okada [1992] and others, this work has extended several elastic crack solutions to provide tilt calculations. The solutions include constant-pressure 2D, penny-shaped, and 3D-elliptic cracks and a 2D-variable-pressure crack. Equations are developed for an arbitrary inclined fracture in an infinite elastic space. Effects of fracture height, fracture length, fracture dip, fracture azimuth, fracture width and monitoring distance on the tilt distribution are given, as well as comparisons with the dislocation model. The results show that the tilt measurements are very sensitive to the fracture dimensions, but also that it is difficult to separate the competing effects of the various parameters.
Date: January 5, 2000
Creator: Warpinski, N.R.
Partner: UNT Libraries Government Documents Department

The bridge permeameter; An alternative method for single-phase, steady-state permeability measurements

Description: Laboratory measurements of single-phase, steady-state permeability of porous rock are important for a number of different applications. The oil and gas industry uses permeability data as a key indicator of the producability of a hydrocarbon reservoir; effective containment of large volumes of oil in underground salt caverns is directly dependent upon the permeability of the adjacent cavern walls; and safe, long term underground isolation of radioactive and hazardous waste is contingent upon the flow and transport characteristics of the surrounding geologic formations. An alternative method for measuring single-phase, steady-state permeability of porous rock is presented. The use of troublesome and expensive mass flow meters is eliminated and replaced with a bridge configuration of flow resistors. Permeability values can be determined directly from differential pressures across the bridge network, resulting in potentially significant cost savings and simplification for conducting these types of measurements. Results from the bridge permeameter are compared with results obtained using conventional methods.
Date: March 1, 1994
Creator: Graf, D.C. & Warpinski, N.R.
Partner: UNT Libraries Government Documents Department

Microseismic and deformation imaging of hydraulic fracture growth and geometry in the C sand interval, GRI/DOE M-Site project

Description: Six hydraulic-fracture injections into a fluvial sandstone at a depth of 4300 ft were monitored with multi-level tri-axial seismic receivers in two wells and an inclinometer array in one well, resulting in maps of the growth and final geometry of each fracture injection. These diagnostic images show the progression of height and length growth with fluid volume, rate and viscosity. Complexities associated with shut downs and high treatment pressures can be observed. Validation of the seismic geometry was made with the inclinometers and diagnostic procedures in an intersecting well. Fracture information related to deformation, such as fracture closure pressure, residual widths, and final prop distribution, were obtained from the inclinometer data.
Date: August 1, 1997
Creator: Warpinski, N.R.; Uhl, J.E. & Engler, B.P.
Partner: UNT Libraries Government Documents Department

Geotechnology for low permeability gas reservoirs; [Progress report], April 1, 1992--September 30, 1993

Description: The objectives of this program are (1) to use and refine a basinal analysis methodology for natural fracture exploration and exploitation, and (2) to determine the important characteritics of natural fracture systems for their use in completion, stimulation and production operations. Continuing work on this project has demonstrated that natural fracture systems and their flow characteristics can be defined by a thorough study of well and outcrop data within a basin. Outcrop data provides key information on fracture sets and lithologic controls, but some fracture sets found in the outcrop may not exist at depth. Well log and core data provide the important reservoir information to obtain the correct synthesis of the fracture data. In situ stress information is then linked with the natural fracture studies to define permeability anisotropy and stimulation effectiveness. All of these elements require field data, and in the cases of logs, core, and well test data, the cooperation of an operator.
Date: November 1, 1993
Creator: Lorenz, J.C.; Warpinski, N.R. & Teufel, L.W.
Partner: UNT Libraries Government Documents Department

Fractures and stresses in Bone Spring sandstones

Description: This project is a collaboration between Sandia National Laboratories and Harvey E. Yates Company being conducted under the auspices of the Oil Recovery Technology Partnership. The project seeks to apply perspectives related to the effects of natural fractures, stress, and sedimentology to the simulation and production of low-permeability gas reservoirs to low-permeability oil reservoirs as typified by the Bone Spring sandstones of the Permian Basin, southeast New Mexico. This report presents the results and analysis obtained in 1989 from 233 ft of oriented core, comprehensive suite of logs, various in situ stress measurements, and detailed well tests conducted in conjunction with the drilling of two development wells. Natural fractures were observed in core and logs in the interbed carbonates, but there was no direct evidence of fractures in the sandstones. However, production tests of the sandstones indicated permeabilities and behavior typical of a dual porosity reservoir. A general northeast trend for the maximum principal horizontal stress was observed in an elastic strain recovery measurements and in strikes of drilling-induced fractures; this direction is subparallel to the principal fracture trend observed in the interbed carbonates. Many of the results presented are believed to be new information for the Bone Spring sandstones. 57 figs., 18 tabs.
Date: September 1, 1990
Creator: Lorenz, J.C.; Warpinski, N.R.; Sattler, A.R. & Northrop, D.A.
Partner: UNT Libraries Government Documents Department

Multiwell experiment: Overview

Description: This field laboratory has been established about 7 mi southwest of Rifle, Colorado. Here the Mesaverde formation lies at a depth of 4000 to 8250 ft. This interval contains different, distinct reservoir types depending upon their depositional environments. These different zones serve as the focus of the various testing and stimulation programs. One key to the Multiwell Experiment is three closely spaced wells. Their 110 to 215 ft separation at depth is less than the nominal dimensions of the lenses in the area. Core, log, well testing, and well-to-well seismic data are providing a far better definition of the geological setting than has been available previously. Comprehensive logging and core analysis programs were conducted. The closely spaced wells also allow interference and tracer tests to obtain in situ reservoir parameters. The vertical variation of in situ stress throughout the intervals of interest is being measured. A series of stimulation experiments is being conducted in one well and the other two wells are being used as observation wells for improved fracture diagnostics and well testing. Another key to achieving the Multiwell Experiment objectives is the synergism resulting from a broad spectrum of activities: geophysical surveys, sedimentological studies, core and log analyses, well testing, in situ stress determination, stimulation, fracture diagnostics, and reservoir analyses. The results from the various activities will define the reservoir and the hydraulic fracture. These, in turn, define the net pay stimulated: the intersection of a hydraulic fracture of known geometry with a reservoir of known morphology and properties. These definitions are further enhanced by the fact that most data will come from closely spaced wells. Thus, spatial variations in reservoir properties can be quantified. 10 refs.
Date: January 1, 1987
Creator: Lorenz, J.C.; Sattler, A.R.; Warpinski, N.R.; Thorne, B.J. & Branagan, P.T.
Partner: UNT Libraries Government Documents Department

Multiwell experiment

Description: The Multiwell Experiment is a research-oriented field laboratory. Its overall objectives are to characterize lenticular, low-permeability gas reservoirs and to develop technology for their production. This field laboratory has been established at a site in the east-central Piceance basin, Colorado. Here the Mesaverde formation lies at a depth of 4000 to 8250 ft. This interval contains different, distinct reservoir types depending upon their depositional environments. These different zones serve as the focus of the various testing and stimulation programs. Field work began in late 1981 and is scheduled through mid-1988. One key to the Multiwell Experiment is three closely spaced wells. Core, log, well testing, and well-to-well seismic data are providing a far better definition of the geological setting than has been available previously. The closely spaced wells also allow interference and tracer tests to obtain in situ reservoir parameters. The vertical variation of in situ stress throughout the intervals of interest is being measured. A series of stimulation experiments is being conducted in one well and the other two wells are being used as observation wells for improved fracture diagnostics and well testing. Another key to achieving the Multiwell Experiment objectives is the synergism resulting from a broad spectrum of activities: geophysical surveys, sedimentological studies, core and log analyses, well testing, in situ stress determination, stimulation, fracture diagnostics, and reservoir analyses. The results from the various activities will define the reservoir and the hydraulic fracture. These, in turn, define the net pay stimulated: the intersection of a hydraulic fracture of known geometry with a reservoir of known morphology and properties. Accomplishments of the past year are listed. 4 refs.
Date: January 1, 1985
Creator: Sattler, A.R.; Warpinski, N.R.; Lorenz, J.C.; Hart, C.M. & Branagan, P.T.
Partner: UNT Libraries Government Documents Department

Laboratory investigation on the effect of in situ stresses on hydraulic fracture containment

Description: Laboratory experiments have been conducted to determine the effect of in situ stress variations on hydraulic fracture containment. Fractures were initiated in layered rock samples with prescribed stress variations, and fracture growth characteristics were determined as a function of stress levels. Stress contrasts of 2-3 MPa were found to be sufficient to restrict fracture growth in laboratory samples of Nevada tuff and Tennessee and Nugget sandstones. The required stress level was found not to depend on mechanical rock properties. However, permeability and the resultant pore pressure effects were found to be important. Tests conducted at bimaterial interfaces between Nugget and Tennessee sandstone show that the resultant stresses set up near the interface due to the applied overburden stress affect the fracture behavior in the same way as the applied confining stresses. These results provide a guideline for determining the in situ stress contrast necessary to contain a fracture in a field treatment.
Date: January 1, 1981
Creator: Warpinski, N.R.; Clark, J.A.; Schmidt, R.A. & Huddle, C.W.
Partner: UNT Libraries Government Documents Department

Observations of broad-band micro-seisms during reservoir stimulation

Description: During hydrocarbon reservoir stimulation such as hydraulic fracturing, the cracking and slippage of the formation results in the emission of seismic energy. The objective of this study was to determine the properties of these induced micro-seisms. A hydraulic fracture experiment was performed in the Piceance Basin of Western Colorado to induce and record micro-seismic events. The formation was subjected to four processes; breakdown/ballout, step-rate test, KCL mini-fracture, and linear-gel mini-fracture. Micro-seisms were acquired with an advanced three-component wall-locked seismic accelerometer package, placed in an observation well 211 ft offset from the well. During the two hours of formation treatment, more than 1200 micro-seisms with signal-to-noise ratios in excess of 20 dB were observed. The observed micro-seisms had a nominally flat frequency from 100 Hz to 1500 Hz and lack the spurious tool-resonance effects evident in previous attempts to measure micro-seisms. Both p-wave and s-wave arrivals are clearly evident in the data set, and hodogram analysis yielded coherent estimates of the event locations. This paper describes the characteristics of the observed micro-seismic events (event occurrence, signal-to-noise ratios, and bandwidth) and illustrates that the new acquisition approach results in enhanced detectability and event location resolution.
Date: April 1, 1993
Creator: Sleefe, G. E.; Warpinski, N. R. & Engler, B. P.
Partner: UNT Libraries Government Documents Department

Comparison and verification of two models which predict minimum principal in situ stress from triaxial data

Description: This paper evaluates the correlation between values of minimum principal in situ stress derived from two different models which use data obtained from triaxial core tests and coefficient for earth at rest correlations. Both models use triaxial laboratory tests with different confining pressures. The first method uses a vcrified fit to the Mohr failure envelope as a function of average rock grain size, which was obtained from detailed microscopic analyses. The second method uses the Mohr-Coulomb failure criterion. Both approaches give an angle in internal friction which is used to calculate the coefficient for earth at rest which gives the minimum principal in situ stress. The minimum principal in situ stress is then compared to actual field mini-frac test data which accurately determine the minimum principal in situ stress and are used to verify the accuracy of the correlations. The cores and the mini-frac stress test were obtained from two wells, the Gas Research Institute`s (GRIs) Staged Field Experiment (SFE) no. 1 well through the Travis Peak Formation in the East Texas Basin, and the Department of Energy`s (DOE`s) Multiwell Experiment (MWX) wells located west-southwest of the town of Rifle, Colorado, near the Rulison gas field. Results from this study indicates that the calculated minimum principal in situ stress values obtained by utilizing the rock failure envelope as a function of average rock grain size correlation are in better agreement with the measured stress values (from mini-frac tests) than those obtained utilizing Mohr-Coulomb failure criterion.
Date: November 1, 1993
Creator: Harikrishnan, R.; Hareland, G. & Warpinski, N. R.
Partner: UNT Libraries Government Documents Department

Microseismic Monitoring of the Mounds Drill Cuttings Injection Tests

Description: This paper describes the microseismic mapping of repeated injections of drill cuttings into two separate formations at a test site near Mounds, OK. Injections were performed in sandstone and shale formations at depths of 830 and 595 m, respectively. Typical injection disposal was simulated using multiple small-volume injections over a three-day period, with long shut-in periods interspersed between the injections. Microseismic monitoring was achieved using a 5-level array of wireline-run, triaxial- accelerometer receivers in a monitor well 76 m from the disposed well. Results of the mapped microseismic locations showed that the disposal domti W= generally aligns with the major horizontal stress with some variations in azimuth and that wide variations in height and length growth occurred with continued injections. These experiments show that the cuttings injection process cm be adequately monitored from a downhole, wireline-run receiver array, thus providing process control and environmental assurance.
Date: January 25, 1999
Creator: Branagan, P.T.; Mahrer, K.D.; Moschovidis, Z.A.; Warpinski, N.R. & Wolhart, S.L.
Partner: UNT Libraries Government Documents Department

Core based stress measurements: A guide to their application. Topical report, July 1991--June 1993

Description: This report is a summary and a guide to core-based stress measurements. It covers anelastic strain recovery, circumferential velocity anistropy, differential strain curve analysis, differential wave velocity analysis, petrographic examination of microcracks, overcoring of archieved core, measurements of the Kaiser effect, strength anisotropy tests, and analysis of coring-induced fractures. The report begins with a discussion of the stored energy within rocks, its release during coring, and the subsequent formation of relaxation microcracks. The interogation or monitoring of these microcracks form the basis for most of the core-based techniques (except for the coring induced fractures). Problems that can arise due to coring or fabric are also presented, Coring induced fractures are discussed in some detail, with the emphasis placed on petal (and petal-centerline) fractures and scribe-knife fractures. For each technique, a short description of the physics and the analysis procedures is given. In addition, several example applications have also been selected (where available) to illustrate pertinent effects. This report is intended to be a guide to the proper application and diagnosis of core-based stress measurement procedures.
Date: June 1, 1993
Creator: Warpinski, N. R.; Teufel, L. W.; Lorenz, J. C. & Holcomb, D. J.
Partner: UNT Libraries Government Documents Department

Introduction to the GRI/DOE Field Fracturing Multi-Site Project

Description: The objective of the Field Fracturing Multi-Sites Project is to conduct field experiments and analyze data that will result in definitive determinations of hydraulic fracture dimensions using remote well and treatment well diagnostic techniques. In addition, experiments will be conducted to provide data that will resolve significant unknowns with regard to hydraulic fracture modeling, fracture fluid rheology and fracture treatment design. These experiments will be supported by a well-characterized subsurface environment, as well as surface facilities and equipment that are conducive to acquiring high-quality data. It is anticipated that the primary benefit of the project experiments will be the development and widespread commercialization of new fracture diagnostics technologies to determine fracture length, height, width and azimuth. Data resulting from these new technologies can then be used to prove and refine the 3D fracture model mechanisms. It is also anticipated that data collected and analyzed in the project will define the correct techniques for determining fracture closure pressure. The overall impact of the research will be to provide a foundation for a fracture diagnostic service industry and hydraulic fracture optimization based on measured fracture response.
Date: December 31, 1993
Creator: Peterson, R. E.; Middlebrook, M. L.; Warpinski, N. R.; Cleary, M. P. & Branagan, P. T.
Partner: UNT Libraries Government Documents Department

Evaluation of a downhole tiltmeter array for monitoring hydraulic fractures

Description: A series of hydraulic-fracture experiments using a downhole tiltmeter array, called an inclinometer array, was conducted at the Department of Energy (DOE)/Gas Research Institute (GRI) Multi-Site facility in Colorado. The inclinometer array was used to measure the deformation of the reservoir rock in response to hydraulic fracture opening and confirm microseismically measured results. In addition, the inclinometer array was found to be a useful tool for accurately measuring closure stress, measuring residual widths of both propped and unpropped fractures, estimating proppant distribution, and evaluating values of in situ moduli.
Date: March 1, 1997
Creator: Warpinski, N.R.; Engler, B.P.; Branagan, P.T.; Wilmer, R. & Wolhart, S.L.
Partner: UNT Libraries Government Documents Department

Microseismic monitoring of the B-sand hydraulic fracture experiment at the DOE/GRI multi-site project

Description: Six hydraulic-fracture injections into a fluvial sandstone at a depth of 4500 ft were monitored with multi-level triaxial seismic receivers in two wells, resulting in maps of the growth and final geometry of each fracture based upon microseismic activity. These diagnostic images show that the hydraulic fractures are highly contained for smaller-volume KCl-water injections, but height growth is significant for the larger-volume, higher-rate, higher-viscosity treatments. Fracture lengths for most injections are similar. Final results are also compared with fracture models.
Date: November 1996
Creator: Warpinski, N. R.; Wright, T. B.; Peterson, R. E. & Branagan, P. T.
Partner: UNT Libraries Government Documents Department

Review of hydraulic fracture mapping using advanced accelerometer-based receiver systems

Description: Hydraulic fracturing is an important tool for natural gas and oil exploitation, but its optimization has been impeded by an inability to observe how the fracture propagates and what its overall dimensions are. The few experiments in which fractures have been exposed through coring or mineback have shown that hydraulic fractures are complicated multi-stranded structures that may behave much differently than currently predicted by models. It is clear that model validation, fracture optimization, problem identification and solution, and field development have all been encumbered by the absence of any ground truth information on fracture behavior in field applications. The solution to this problem is to develop techniques to image the hydraulic fracture in situ from either the surface, the treatment well, or offset wells. Several diagnostic techniques have been available to assess individual elements of the fracture geometry, but most of these techniques have limitations on their usefulness. For example, tracers and temperature logs can only measure fracture height at the wellbore, well testing and production history matching provide a productive length which may or may not be different from the true fracture length, and tiltmeters can provide accurate information on azimuth and type of fracture (horizontal or vertical), but length and height can only be extracted from a non-unique inversion of the data. However, there is a method, the microseismic technique, which possesses the potential for imaging the entire hydraulic fracture and, more importantly, its growth history. This paper discusses application of advanced technology to the microseismic method in order to provide detailed accurate images of fractures and their growth processes.
Date: March 1, 1997
Creator: Warpinski, N.R.; Uhl, J.E. & Engler, B.P.
Partner: UNT Libraries Government Documents Department

Application of microseismic technology to hydraulic fracture diagnostics: GRI/DOE Field Fracturing Multi-Sites Project

Description: The objective of the Field Fracturing Multi-Sites Project (M-Site) is to conduct field experiments and analyze data that will result in definitive determinations of hydraulic fracture dimensions using remote well and treatment well diagnostic techniques. In addition, experiments will be conducted to provide data that will resolve significant unknowns with regard to hydraulic fracture modeling, fracture fluid rheology and fracture treatment design. These experiments will be supported by a well-characterized subsurface environment as well as surface facilities and equipment conducive to acquiring high-quality data. It is anticipated that the project`s research advancements will provide a foundation for a fracture diagnostic service industry and hydraulic fracture optimization based on measured fracture response. The M-Site Project is jointly sponsored by the Gas Research Institute (GRI) and the US Department of Energy (DOE). The site developed for M-Site hydraulic fracture experimentation is the former DOE Multiwell Experiment (MWX) site located near Rifle, Colorado. The MWX project drilled three closely-spaced wells (MWX-1, MWX-2 and MWX-3) which were the basis for extensive reservoir analyses and tight gas sand characterizations in the blanket and lenticular sandstone bodies of the Mesaverde Group. The research results and background knowledge gained from the MWX project are directly applicable to research in the current M-Site Project.
Date: June 1995
Creator: Wilmer, R.; Warpinski, N. R.; Wright, T. B.; Branagan, P. T. & Fix, J. E.
Partner: UNT Libraries Government Documents Department