The hydraulic testing of pre-existing fractures(HTPF)is one of the most promising in situ stress measurement methods,particularly for three-dimensional stress tensor determination.However,the stress tensor determinati...The hydraulic testing of pre-existing fractures(HTPF)is one of the most promising in situ stress measurement methods,particularly for three-dimensional stress tensor determination.However,the stress tensor determination based on the HTPF method requires at least six tests or a minimum of 14-15 tests(under different conditions)for reliable results.In this study,we modified the HTPF method by considering the shear stress on each pre-existing fracture,which increased the number of equations for the stress tensor determination and decreased the number of tests required.Different shear stresses were attributed to different fractures by random sampling;therefore,the stress tensors were obtained by searching for the optimal solution using the least squares criterion based on the Monte Carlo method.Thereafter,we constrained the stress tensor based on the tensile strength criterion,compressive strength criterion,and vertical stress constraints.The inverted stress tensors were presented and analyzed based on the tensorial nature of the stress using the Euclidean mean stress tensor.Two stress-measurement campaigns in Weifang(Shandong Province,China)and Mercantour road tunnel(France)were implemented to highlight the validity and efficiency of the modified HTPF(M-HTPF)method.The results showed that the M-HTPF method can be applied for stress tensor inversion using only three to four tests on pre-existing fractures,neglecting the stress gradient.The inversion results were confined to relatively small distribution dispersions and were significantly reliable and stable due to the shear stresses on the fractures and the stress constraints employed.The M-HTPF method is highly feasible and efficient for complete stress tensor determination in a single borehole.展开更多
The Mesozoic Yanshanian Movement affected the tectonic evolution of the North China Craton(NCC).It is proposed that Mesozoic cratonic destruction peaked~125 Ma,possibly influenced by subduction of the western Pacific ...The Mesozoic Yanshanian Movement affected the tectonic evolution of the North China Craton(NCC).It is proposed that Mesozoic cratonic destruction peaked~125 Ma,possibly influenced by subduction of the western Pacific Plate beneath the Euro-Asian Plate in the Early Cretaceous.The southern Jinzhou area in the eastern block of the NCC preserves clues about the tectonic events and related geological resources.Studies of the regional stress field evolution from the Cretaceous to the Cenozoic can enhance our understanding of the tectonics and dynamics of the NCC.Borehole image logging technology was used to identify and collect attitudes of tensile fractures from 11 boreholes;these were subdivided into four groups according to dip direction,i.e.,NNW-SSE,NWW-SEE,W-E and NE-SW.The development of these fractures was controlled primarily by the regional tectonic stress field;temperature,lithology,and depth contributed to some extent.In 136-125 Ma in the Early Cretaceous,the area was characterized by extension that was oriented NNW-SSE and NWW-SEE;from 125-101 Ma the extension was oriented W-E;after 101 Ma it was NE-SW.This counterclockwise trend has persisted to the present,probably related to oblique subduction of the Pacific Plate,and is characterized by ongoing extension that is nearly N-S-oriented and NEE-SWW-oriented compression.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.42174118)a research grant(Grant No.ZDJ 2020-7)from the National Institute of Natural Hazards,Ministry of Emergency Management of China.
文摘The hydraulic testing of pre-existing fractures(HTPF)is one of the most promising in situ stress measurement methods,particularly for three-dimensional stress tensor determination.However,the stress tensor determination based on the HTPF method requires at least six tests or a minimum of 14-15 tests(under different conditions)for reliable results.In this study,we modified the HTPF method by considering the shear stress on each pre-existing fracture,which increased the number of equations for the stress tensor determination and decreased the number of tests required.Different shear stresses were attributed to different fractures by random sampling;therefore,the stress tensors were obtained by searching for the optimal solution using the least squares criterion based on the Monte Carlo method.Thereafter,we constrained the stress tensor based on the tensile strength criterion,compressive strength criterion,and vertical stress constraints.The inverted stress tensors were presented and analyzed based on the tensorial nature of the stress using the Euclidean mean stress tensor.Two stress-measurement campaigns in Weifang(Shandong Province,China)and Mercantour road tunnel(France)were implemented to highlight the validity and efficiency of the modified HTPF(M-HTPF)method.The results showed that the M-HTPF method can be applied for stress tensor inversion using only three to four tests on pre-existing fractures,neglecting the stress gradient.The inversion results were confined to relatively small distribution dispersions and were significantly reliable and stable due to the shear stresses on the fractures and the stress constraints employed.The M-HTPF method is highly feasible and efficient for complete stress tensor determination in a single borehole.
基金supported by the National Natural Science Foundation of China(41574088)。
文摘The Mesozoic Yanshanian Movement affected the tectonic evolution of the North China Craton(NCC).It is proposed that Mesozoic cratonic destruction peaked~125 Ma,possibly influenced by subduction of the western Pacific Plate beneath the Euro-Asian Plate in the Early Cretaceous.The southern Jinzhou area in the eastern block of the NCC preserves clues about the tectonic events and related geological resources.Studies of the regional stress field evolution from the Cretaceous to the Cenozoic can enhance our understanding of the tectonics and dynamics of the NCC.Borehole image logging technology was used to identify and collect attitudes of tensile fractures from 11 boreholes;these were subdivided into four groups according to dip direction,i.e.,NNW-SSE,NWW-SEE,W-E and NE-SW.The development of these fractures was controlled primarily by the regional tectonic stress field;temperature,lithology,and depth contributed to some extent.In 136-125 Ma in the Early Cretaceous,the area was characterized by extension that was oriented NNW-SSE and NWW-SEE;from 125-101 Ma the extension was oriented W-E;after 101 Ma it was NE-SW.This counterclockwise trend has persisted to the present,probably related to oblique subduction of the Pacific Plate,and is characterized by ongoing extension that is nearly N-S-oriented and NEE-SWW-oriented compression.