Head injury is often attributed to transient shear stresses arising from rotation of the brain in the cranial cavity. This paper deals with the experimental determination and analytical characterization of in vitro human brain dynamic constitutive properties in pure shear. A closed loop, feedback torsional system with a self mass cancelling torque transducer is used for the experimental study. Values of the storage and loss components of the dynamic shear modulus are computed and a four parameter, linear, visco-elastic model representing brain tissue properties up to 350 Hz is presented. In addition, failure criterion in terms of limiting strains and strain rates are identified.

Mechanical properties of coal have been determined in an effort to advance in situ coal gasification technology. Tests and apparatus were developed to evaluate the directional compressive and shear properties of coal at elevated temperatures. Both creep and stress-relaxation experiments were conducted to evaluate the creep compliance and stress-relaxation properties in compression and shear, at temperatures between 75° and 650°F (24° and 343°C), for the face cleat, butt cleat and normal to coalbed orientation, and four different specimen sizes. Stress-strain relations and ultimate strengths were also determined at three different loading rates for these directions and temperatures. A shift function was used to represent the creep and stress relaxation properties as functions of time and temperature. Four- and six-parameter viscoelastic fluid models were used to represent the data over the time-temperature ranges. Shallow and deep mine coal from the Pittsburgh coalbed was tested. The coal was found to have the greatest ultimate strength and elastic moduli at 200°F (93°C) in all directions in both compression and shear, and to be specimen size dependent. The ultimate strength in the normal to coalbed direction was approximately twice that in the face and butt cleat directions at all temperatures. At 575° to 650°F (302° – 343°C), the coal becomes fluidic and is well represented by a four-parameter fluid model. It also obeys the time-temperature superposition principle.

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American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. This paper was prepared for the 49th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Texas, Oct. 6–9, 1974. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract Hydraulic fracturing of oil and gas bearing sandstone formations to enhance recovery is still being done today without any means of determining the actual types, lengths, or directions of fractures induce away from the wellbore. The mechanics of hydraulic fracturing processes affecting the acoustic mapping of fractures, the associated crack and wave propagation phenomena, monitoring system requirements, an example of a monitoring system used, and field experiments conducted to date by the Morgantown Energy Research Center, U.S. Bureau of Mines are discussed. Applications of the fracture mapping technique, if proven successful could lead to improved well location design and fracturing treatments for more efficient petroleum and natural gas recovery, solution mining, in situ coal gasification and liquefaction, subsurface waste disposal, oil shale and geothermal energy extraction, and perhaps others. Preliminary analysis of the data indicates that the fractures propagate in discrete phases or arc lengths during which sufficient acoustic emissions occur to allow the fractures to be mapped, and that the best bandwidth for monitoring the acoustic emission may be the 80 to 500 Hz range. Introduction Hydraulic fracturing of oil and gas bearing formations to increase recovery has been a practice since the late 1940's. Although many practice since the late 1940's. Although many schemes of calculating fracture lengths and predicting the directions have been devised, no predicting the directions have been devised, no direct means of measuring the number, types, lengths, directions, or rates of growth of induced fractures exists today. Wellbore post-fracture measurements, including impression post-fracture measurements, including impression packers, are presently the best means of direct packers, are presently the best means of direct measurement of induced fracture orientations. These observations, however, are not necessarily valid a few inches away from the wellbore. Further development of hydraulic fracturing technology depends upon a more immediate means of measuring results. Accurate and immediate measurement of the fracture directions for only a few wells in a new reservoir could allow systematic development for maximum and more economical recovery.

The use of a multisensor array has shown that hydraulic pressurization can be useful in delineating subsurface fracture systems in petroleum reservoirs. It can help in establishing effective patterns of injection and production wells to avoid premature waterfront break-through, and thus increase sweep efficiency and oil recovery in flooding operations. Introduction Well stimulation by hydraulic fracturing is often a prerequisite to effective oil recovery by prerequisite to effective oil recovery by waterflooding, but acceptance of this idea has been inhibited by fears that fractures would permit channeling of the displacing fluid and bypassing of oil. Donahue et al. conducted model studies of a five-spot pilot flood and found that different orientations of the pattern significantly affected the sweep efficiencies at pattern significantly affected the sweep efficiencies at breakthrough (Fig. 1). Others report that consideration must be given to the type of fracture to be formed and to the presence of natural fluid conduits in the subsurface formation of the reservoir. Hubbert and Willis, Heck, Kehle, and Dunlap report that induced fractures will be vertical and will extend in a compass direction usually dictated by the earth stresses. Their studies show that the most probable direction that will be assumed by induced fractures can be estimated with some accuracy from a study of the principal horizontal tectonic stresses. However, communication between wells or between zones and the direction of magnitude of natural fracture trends must also be delineated . The pattern of injection and production wells can then be established to make maximum economic use of the subsurface natural and induced fracture system. For the Appalachian area, considerable data have been obtained from surface studies of joints and lineaments on the direction preferred by induced hydraulic fractures and on orientation predictions. This seems to confirm the work of Heck who concluded earlier that reservoir rocks and surface rocks are jointed similarly, except that the subsurface joints are relatively closed and exist as planes of weakness. We shall describe here a field experiment designed to establish a technique for delineating the subsurface fracture system in a petroleum reservoir. Essentially, the procedure employed is an interference test that was modified by the addition of a multisensor array of pressure transducers to measure responses simultaneously and at considerable distances from the test well. The test site is adjacent to leases where joint and lineament strikes, directional permeability, and the orientations of induced hydraulic fractures were measured in the manner described by Anderson and Stahl. We shall describe the instrumentation and tests that were employed, and interpret the fracture trends from this field experiment. The Bradford Test Site Description and Location A 36-acre tract about 10 miles east of Bradford, Pa., was made available for this research by the Minard Run Oil Co. (See Fig. 2.) Open-hole completion practices were used and considerable subsurface data were practices were used and considerable subsurface data were available in the form of cores, electric logs, and wellbore impression-packer surveys. The orientation of induced hydraulic fractures was compared with surface joint measurements.