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Finite element model simulations associated with hydraulic fracturing
127A
826017 LABORATORY INVESTIGATION ON THE EFFECT OF INSITU STRESSES ON HYDRAULIC FRACTURE CONTAINMENT Warplnski, N R; Clark, J A; Schmidt, R A SOC Pet Engr J, V22, N3, June 1982, P333-340 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 level. Stress contrasts of 2-3MPa were founi sufficient to restrict fracture growth in laboratory samples of Nevada tuff and Tennessee a~d Nugget sandstones. The required stress level was found not to depend on mechanical rock properties. However, permeability and the resultant pare pressure effects were important. Tests conducted at bimaterial interfaces between Nugget and Tennessee sandstones show that the resultant stresses set up near the interface because of the applied everburden stress affect the fracture behavior in the same way as the applied confining stresses. 826018 HYDRAULIC FRACTURE GEOMETRY: FRACTURE CONTAINMENT IN LAYERED FORMATIONS Van Eekelen, H A M Soc Pet Engr J, V22, N3, June 1982, P341-349 The problem of hydraulic fracture containment is considered. The concepts of stress intensity factor and fracture toughness are introduced, and it is shown that local contaimment effects around the upper and lower crack edge, which decrease the stress intensity factor or increase the fracture toughness, are only of minor importance. Global containment effects caused by contrasts i n stiffness and in sltu stress between the pay zone and adjoining layers and which limit the penetration depth of the fracture are then discussed. For the case of a stiffness contrast, an estimate of the penetration depth is given. 35 reds. 826019 FINITE E L ~ N T WITH HYDRAULIC Advanl, S H; Soc Pet Engr
MODEL SIMULATIONS ASSOCIATED FRACTURING Lee, J K J, V22, N2, April 1982, P209-218
A vertical hydraulic fracture model is formulated. Simulations of the vertical hydraulic fracture model, with the effects of multilayering and in sltu stress considered, are presented, simulations associated with dendritic fracturing and Joint interaction which entail mixed-mode conditions are then considered. 30 refs. 826020 FRACTURE OF MARBLEs IN THE FLEXURAL TEST UNDER CONFINING PRESSURE (IN JAPANESE) Matsuki, K; Kobayashl, R; Yoshida, T J Min Metall Inst Japan, V97, Nlll6, 19811982, P63-88 Four point bending tests were u r ~ t a k e n i n a triaxial vessel for fine grained and coarse grained Akiyoshi marbles. Results showed that: (i) fracture propagation is more stable under high than under low confining pressures, (2) fine grained samples show a drop in bending moment on initiation of fracture whereas in in coarse-grained samples beniing moment increases till rupture, (3) the outer fibre bending stress at fracture initiation increases with confining pressure in both sample types, (h) the number of fracture cracks initiated
increases with confining pressure and decreases with specimen thickness, whereas the crack length to thickness ratio decreases with increase of both confining pressure and specimen thickne ss.
Strength characteristics 826021 SHEAR BEHAVIOUR OF BEDDING PLANES IN MT MCRAE SHALE WITH IMPLICATIONS FOE ROCK SLOPE DESIGN. TECHNICAL NOTE Lilly, P A Int J Rock Mech Min Sci, VI9, N4, Aug 1962, F205-209 Shear tests were carried out on core samples of Mr. McRae shale in the field. Shear strength data was obtained, ani shear stress/normal stress data, which was used to calculate friction parameters. An approach for using this data in practical slope design is then suggested. 826022 DETERMINATION OF SUBCOAL STRATA STRENGTH USING ULTRASONIC TESTING Tillman, S M B~II Assoc Engng Geol, VIg, NI, Feb 1982, P77-86 An investigation to attempt to correlate shear strength anl ultrasonic wave velocities of subcoal strata are described. Samples used were obtained from ll coal mine floor borings. Results from the ultrasonic testing were compared with the shear stremgth values determined from unlrained triaxial, and unconfined compression strength tests. Significant correlations were noted to exist between mean wave velocities. 826023 PERFORMANCE OF IMPERMEABLE AND PERMEABLE REINFORC~MENT IN CLAY SUBJECT TO UNDRAINED LOADING Ingold, T S; Miller, K S Q J Engng Geol, VI5, NB, 1982, P201-208 Four series of undrained shear tests were carried out on two clay soils (kaolin and London clay) and two types of reinforcement materials. Results showed that clay reinforced with impermeable aluminium foll suffered a decrease in strength when subject to undrained loading. Subsequent tests involving porewater pressure measurement indicated that this was due to a reduction in minor principal effective stress caused by generation and radial migration of high porewater pressures in the sample. Results for clay reinforced with porous plastic showed an increase in strength of the clay as the reinforcement spacing decreased, ultimately exceeding the unrelnforced strength. Investigation of porewater pressure response showed that although high porewater pressure was induced during testing, it dissipates to the reinforcement 826024 THEORETICAL ANALYSIS OF THE FALL CONE TEST Houlsby, G T Geotechnique, V32, N2, June 1982, Plll-ll8 Presents a theoretical analysis of the fall cone test and a direct calculation of the undrained strength at the liquid limit° The analysis also allows a critical examination of the tolerances specified for the liquid limit device: it is found that the single most important factor affecting liquid limit is cone roughness.
826017 LABORATORY INVESTIGATION ON THE EFFECT OF INSITU STRESSES ON HYDRAULIC FRACTURE CONTAINMENT Warplnski, N R; Clark, J A; Schmidt, R A SOC Pet Engr J, V22, N3, June 1982, P333-340 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 level. Stress contrasts of 2-3MPa were founi sufficient to restrict fracture growth in laboratory samples of Nevada tuff and Tennessee a~d Nugget sandstones. The required stress level was found not to depend on mechanical rock properties. However, permeability and the resultant pare pressure effects were important. Tests conducted at bimaterial interfaces between Nugget and Tennessee sandstones show that the resultant stresses set up near the interface because of the applied everburden stress affect the fracture behavior in the same way as the applied confining stresses. 826018 HYDRAULIC FRACTURE GEOMETRY: FRACTURE CONTAINMENT IN LAYERED FORMATIONS Van Eekelen, H A M Soc Pet Engr J, V22, N3, June 1982, P341-349 The problem of hydraulic fracture containment is considered. The concepts of stress intensity factor and fracture toughness are introduced, and it is shown that local contaimment effects around the upper and lower crack edge, which decrease the stress intensity factor or increase the fracture toughness, are only of minor importance. Global containment effects caused by contrasts i n stiffness and in sltu stress between the pay zone and adjoining layers and which limit the penetration depth of the fracture are then discussed. For the case of a stiffness contrast, an estimate of the penetration depth is given. 35 reds. 826019 FINITE E L ~ N T WITH HYDRAULIC Advanl, S H; Soc Pet Engr
MODEL SIMULATIONS ASSOCIATED FRACTURING Lee, J K J, V22, N2, April 1982, P209-218
A vertical hydraulic fracture model is formulated. Simulations of the vertical hydraulic fracture model, with the effects of multilayering and in sltu stress considered, are presented, simulations associated with dendritic fracturing and Joint interaction which entail mixed-mode conditions are then considered. 30 refs. 826020 FRACTURE OF MARBLEs IN THE FLEXURAL TEST UNDER CONFINING PRESSURE (IN JAPANESE) Matsuki, K; Kobayashl, R; Yoshida, T J Min Metall Inst Japan, V97, Nlll6, 19811982, P63-88 Four point bending tests were u r ~ t a k e n i n a triaxial vessel for fine grained and coarse grained Akiyoshi marbles. Results showed that: (i) fracture propagation is more stable under high than under low confining pressures, (2) fine grained samples show a drop in bending moment on initiation of fracture whereas in in coarse-grained samples beniing moment increases till rupture, (3) the outer fibre bending stress at fracture initiation increases with confining pressure in both sample types, (h) the number of fracture cracks initiated
increases with confining pressure and decreases with specimen thickness, whereas the crack length to thickness ratio decreases with increase of both confining pressure and specimen thickne ss.
Strength characteristics 826021 SHEAR BEHAVIOUR OF BEDDING PLANES IN MT MCRAE SHALE WITH IMPLICATIONS FOE ROCK SLOPE DESIGN. TECHNICAL NOTE Lilly, P A Int J Rock Mech Min Sci, VI9, N4, Aug 1962, F205-209 Shear tests were carried out on core samples of Mr. McRae shale in the field. Shear strength data was obtained, ani shear stress/normal stress data, which was used to calculate friction parameters. An approach for using this data in practical slope design is then suggested. 826022 DETERMINATION OF SUBCOAL STRATA STRENGTH USING ULTRASONIC TESTING Tillman, S M B~II Assoc Engng Geol, VIg, NI, Feb 1982, P77-86 An investigation to attempt to correlate shear strength anl ultrasonic wave velocities of subcoal strata are described. Samples used were obtained from ll coal mine floor borings. Results from the ultrasonic testing were compared with the shear stremgth values determined from unlrained triaxial, and unconfined compression strength tests. Significant correlations were noted to exist between mean wave velocities. 826023 PERFORMANCE OF IMPERMEABLE AND PERMEABLE REINFORC~MENT IN CLAY SUBJECT TO UNDRAINED LOADING Ingold, T S; Miller, K S Q J Engng Geol, VI5, NB, 1982, P201-208 Four series of undrained shear tests were carried out on two clay soils (kaolin and London clay) and two types of reinforcement materials. Results showed that clay reinforced with impermeable aluminium foll suffered a decrease in strength when subject to undrained loading. Subsequent tests involving porewater pressure measurement indicated that this was due to a reduction in minor principal effective stress caused by generation and radial migration of high porewater pressures in the sample. Results for clay reinforced with porous plastic showed an increase in strength of the clay as the reinforcement spacing decreased, ultimately exceeding the unrelnforced strength. Investigation of porewater pressure response showed that although high porewater pressure was induced during testing, it dissipates to the reinforcement 826024 THEORETICAL ANALYSIS OF THE FALL CONE TEST Houlsby, G T Geotechnique, V32, N2, June 1982, Plll-ll8 Presents a theoretical analysis of the fall cone test and a direct calculation of the undrained strength at the liquid limit° The analysis also allows a critical examination of the tolerances specified for the liquid limit device: it is found that the single most important factor affecting liquid limit is cone roughness.