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Stress determination from hydraulic tests on preexisting fractures — the H.T.P.F. method
102A 873136 Soft inclusion instrument for in situ stress measurement in
873140 Stress conditions for initiation of secondary fractures from a
coal
fractured borehole
Mills, K W; Pender,M J Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, I-3 Sept 1986 P247-251. Publ Lulea: Centek,1986
Detournay, E; Jeffrey, R G Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P281-288. Publ Lulea: Centek,1986
A soft hollow inclusion strain measuring device that employs the overcoring technique of stress relief is described. The instrument has an inflatable rubber membrane with electrical resistance strain gauges mounted on the outer surface. These strain gauges are bonded with epoxy cement directly to the periphery of a 38ram diameter pilot hole by inflating the rubber membrane. A pressuremeter test can be conducted in situ, prior to the overcoring operation, to verify correct strain gauge operation and to determine the modulus of the rock. The instrument has been used to measure in situ stresses in both a sub-bituminous coal and an anisotropic schist, and also to monitor stress changes in coal. Auth.
A two-dimensional elastic analysis is made of conditions for initiating, by pressurizing a jacketed borehole, secondary fractures that extend perpendicular to the maximum in-situ stress. The problem is uncoupled into two parts: first, the tangential stress is calculated at the points of initiation of the secondary fractures as a function of borehole pressure, far-field stress, and length of the primary fractures; and second, the stable length of the primary fractures is calculated using linear elastic fracture mechanics. This analysis leads to a simple method for determining the principal stress provided the minimum principal stress and the primary and secondary breakdown pressures are known, and does not require determination of the tensile strength of the rock. Auth.
873137 Rock stress determinations with the STT and SFJ techniques
Pinto, J L; Cunha, A P Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P253-260. Publ Lulea: Centek,1986 A brief review of the Stress Tensor Tube (STI') and the Small Flat Jack (SFJ) methods, developed at the LNEC, is presented and the most recent advances concerning apparatus, testing and interpretation of results are pointed out. A synthesis of the data collected by the LNEC about the initial stress fields in rock masses is presented, as well as some significant applications of rock stress measurements in the design of structures. 873138 In-situ validation of the borehole slotting stressmeter Bock, H Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P261-270. Publ Lulea: Centek,1986 A recently developed 2-D stressmeter, the borehole slotter, is reuseable, completely self-contained in both its stress release operations and its strain measuring capabilities, and allows for a large number of measurements at very reasonable costs. Extensive in-situ tests at the Burdekin Falls damsite, Queensland, Australia, have been carried out in parallel with overcoring and hydraulic fracturing tests. The borehole slotting technique was found to have major advantages over the established methods with regard to speed of operation, reliability and economy. 873139 Borehole breakouts - a new tool for estimating in situ stress?
873141 In-situ stress measurements in deep boreholes using hydraulic fracturing, weilbore breakouts, and stonely wave polarization
Zoback, M D; Mastin, L; Barton, C Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P289-299. Publ Lulea: Centek,1986 The potential for making direct measurement of in-situ stress magnitudes at mid-crustal depth using three methods is discussed. The usefulness of hydraulic fracturing in deep boreholes is discussed and it is demonstrated that extremely high breakdown and fracture extension pressures will be required at depth, especially in compressional tectonic environments. As wellbore breakouts are likely to occur in deep boreholes and could make hydraulic fracturing extremely difficult, the potential for estimating stress magnitudes through analysis of the breakouts was discussed. Breakouts in the Kola Penninsula hole in the Soviet Union are analysed and the magnitudes of in situ stresses estimated to depths of 11.6km. A new stress measurement method is briefly discussed based on utilization of stress-induced polarization of Stoneley wave particle motions. This method has been successfully used to determine stress orientation in several wells and has the potential for estimation of relative stress magnitudes.
873142 Stress determination from hydraufic tests on preexisting fractures - the H.T.P.F. method
Haimson, B C; Herrick, C G Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P271-280. Publ Lulea: Centek,1986
Cornet, F H Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P301-312. Publ Lulea: Centek,1986
An initial experimental program studying the relationship between borehole breakout formation in Indiana limestone and the in-situ state of stress was carried out. It is confirmed that breakouts occur in two diametrically opposed borehole zones along the direction of the least horizontal principal stress. Thin section analysis suggests that the major breakout mechanism is tensile rupture along surfaces parallel to the borehole wall, aided by shear failure in the radial direction. The potential exists for utilizing breakout geometric parameters to estimate the two horizontal principal in situ stresses. Auth.
A method for determining the complete regional stress field is presented. It is based on measurements of the normal stress supported by preexisting fracture planes (with various dip and strike) by means of hydraulic tests. The solution does not involve the stress field in the immediate vicinity of the well. Two examples concerning granitic rocks are presented. The first one involves fourteen tests between 100m and 973m, the second one sixteen tests between 5ore and 620m. For the second case, a stress discontinuity is observed around 300m. Deep results are coherent with focal mechanisms of microseismic events. Auth.
© 1987 Pergamon Journals Ltd. Reproduction not permitted
873140 Stress conditions for initiation of secondary fractures from a
coal
fractured borehole
Mills, K W; Pender,M J Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, I-3 Sept 1986 P247-251. Publ Lulea: Centek,1986
Detournay, E; Jeffrey, R G Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P281-288. Publ Lulea: Centek,1986
A soft hollow inclusion strain measuring device that employs the overcoring technique of stress relief is described. The instrument has an inflatable rubber membrane with electrical resistance strain gauges mounted on the outer surface. These strain gauges are bonded with epoxy cement directly to the periphery of a 38ram diameter pilot hole by inflating the rubber membrane. A pressuremeter test can be conducted in situ, prior to the overcoring operation, to verify correct strain gauge operation and to determine the modulus of the rock. The instrument has been used to measure in situ stresses in both a sub-bituminous coal and an anisotropic schist, and also to monitor stress changes in coal. Auth.
A two-dimensional elastic analysis is made of conditions for initiating, by pressurizing a jacketed borehole, secondary fractures that extend perpendicular to the maximum in-situ stress. The problem is uncoupled into two parts: first, the tangential stress is calculated at the points of initiation of the secondary fractures as a function of borehole pressure, far-field stress, and length of the primary fractures; and second, the stable length of the primary fractures is calculated using linear elastic fracture mechanics. This analysis leads to a simple method for determining the principal stress provided the minimum principal stress and the primary and secondary breakdown pressures are known, and does not require determination of the tensile strength of the rock. Auth.
873137 Rock stress determinations with the STT and SFJ techniques
Pinto, J L; Cunha, A P Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P253-260. Publ Lulea: Centek,1986 A brief review of the Stress Tensor Tube (STI') and the Small Flat Jack (SFJ) methods, developed at the LNEC, is presented and the most recent advances concerning apparatus, testing and interpretation of results are pointed out. A synthesis of the data collected by the LNEC about the initial stress fields in rock masses is presented, as well as some significant applications of rock stress measurements in the design of structures. 873138 In-situ validation of the borehole slotting stressmeter Bock, H Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P261-270. Publ Lulea: Centek,1986 A recently developed 2-D stressmeter, the borehole slotter, is reuseable, completely self-contained in both its stress release operations and its strain measuring capabilities, and allows for a large number of measurements at very reasonable costs. Extensive in-situ tests at the Burdekin Falls damsite, Queensland, Australia, have been carried out in parallel with overcoring and hydraulic fracturing tests. The borehole slotting technique was found to have major advantages over the established methods with regard to speed of operation, reliability and economy. 873139 Borehole breakouts - a new tool for estimating in situ stress?
873141 In-situ stress measurements in deep boreholes using hydraulic fracturing, weilbore breakouts, and stonely wave polarization
Zoback, M D; Mastin, L; Barton, C Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P289-299. Publ Lulea: Centek,1986 The potential for making direct measurement of in-situ stress magnitudes at mid-crustal depth using three methods is discussed. The usefulness of hydraulic fracturing in deep boreholes is discussed and it is demonstrated that extremely high breakdown and fracture extension pressures will be required at depth, especially in compressional tectonic environments. As wellbore breakouts are likely to occur in deep boreholes and could make hydraulic fracturing extremely difficult, the potential for estimating stress magnitudes through analysis of the breakouts was discussed. Breakouts in the Kola Penninsula hole in the Soviet Union are analysed and the magnitudes of in situ stresses estimated to depths of 11.6km. A new stress measurement method is briefly discussed based on utilization of stress-induced polarization of Stoneley wave particle motions. This method has been successfully used to determine stress orientation in several wells and has the potential for estimation of relative stress magnitudes.
873142 Stress determination from hydraufic tests on preexisting fractures - the H.T.P.F. method
Haimson, B C; Herrick, C G Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P271-280. Publ Lulea: Centek,1986
Cornet, F H Proc International Symposium on Rock Stress and Rock Stress Measurement, Stockholm, 1-3 Sept 1986 P301-312. Publ Lulea: Centek,1986
An initial experimental program studying the relationship between borehole breakout formation in Indiana limestone and the in-situ state of stress was carried out. It is confirmed that breakouts occur in two diametrically opposed borehole zones along the direction of the least horizontal principal stress. Thin section analysis suggests that the major breakout mechanism is tensile rupture along surfaces parallel to the borehole wall, aided by shear failure in the radial direction. The potential exists for utilizing breakout geometric parameters to estimate the two horizontal principal in situ stresses. Auth.
A method for determining the complete regional stress field is presented. It is based on measurements of the normal stress supported by preexisting fracture planes (with various dip and strike) by means of hydraulic tests. The solution does not involve the stress field in the immediate vicinity of the well. Two examples concerning granitic rocks are presented. The first one involves fourteen tests between 100m and 973m, the second one sixteen tests between 5ore and 620m. For the second case, a stress discontinuity is observed around 300m. Deep results are coherent with focal mechanisms of microseismic events. Auth.
© 1987 Pergamon Journals Ltd. Reproduction not permitted