Determination of the three-dimensional in situ stress tensor in inclined boreholes and its application
The conventional hydraulic fracturing(HF)method is greatly limited in the in situ stress measurements of inclined boreholes,especially in three-dimensional stress measurements.Moreover,the hydraulic tests on pre-existing fractures(HTPF)requires a large number of pre-existing fractures to obtain reasonable results.By optimizing the assumption of shear stresses on the primary fracture surfaces and using Monte Carlo algorithm,the three-dimensional stress tensor inversion in the inclined borehole was realized by combining the conventional HF and the HTPF tests.The reliability and accuracy of the proposed method were verified by three-dimensional stress measurements of an inclined borehole in a pumped storage power station in Jizhou,Tianjin.The results show that the proposed method can determine the three-dimensional stress tensors of the inclined borehole only by selecting 1 or more test intervals for conventional HF tests in intact rock mass and 1 or more test intervals for HTPF tests.Compared with the HTPF method that only adopts pre-existing fractures in stress determination,the proposed method greatly reduces the requirement of the number of pre-existing fractures.The inversion results have little dispersion and high stability,which are also consistent with the regional stress state.The proposed method provides a new idea and a reliable approach to determine the stress tensor using a single inclined or vertical borehole.
rock mechanicsinclined boreholethree-dimensional stress tensorhydraulic fracturingpre-existing fracturesMonte Carlo algorithm
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