10:45 AM - 12:15 PM
[SCG61-P01] Some recent findings in simultaneous analysis of rock masses stress state and activity of natural fractures and faults
Keywords:Geomechanics, Stress, Fractures
The study presents several topics related to interrelationships between current stress state of rock mass and history of its evolution on the one hand, and activity of natural fractures and faults existing in it on the other hand. This theme is covered within several blocks roughly related to three different spatial scales: rock sample scale, wellbore scale, and regional scale.
In the first block, the study presents some results of laboratory experiments devoted to predict initiation and propagation of new fractures as well as activation of pre-existing fractures in rock samples subjected to varied loading. Stress vs. strain loading curves obtained from triaxial loading tests are interpreted using non-associated plastic flow law, energy release concept, and brittleness evaluation methods to predict spatial orientations, positions, and effective properties of fractures that become tectonically active at various loading points leading to corresponding changes in the inner structure of the rock. The predictions are consequently checked using analysis of acoustic emission during experiment and detailed studies on rock inner structure using tomography and ultrasonic measurements.
The second block of the study is devoted to relationship between stress state of rock masses and activity of natural fractures that can be analysed through well-logging data. The study presents a modified procedure for evaluating stress state of well surrounding masses based on fluid conductivity of natural fractures existing in it. Two recent results of evaluating stress via this method are presented for specific regions related to subduction zones: Hikurangi Subduction Zone (New Zealand) and Nankai Trough Subduction Zone (Japan). Both regions are characterized with presence of wells with enough logging data to deal with conductivity of natural fractures in well surrounding rock masses, so that stress state can be evaluated. Activity of natural fractures is shown to be a reliable method of stress evaluation via comparing the results with stress estimations performed with conventional methods where possible.
The third block of the study directly broadens the previous scale to regional scale. Recent results of analysing stress state of Nankai Trough Seismogenic Zone from discrete data from wells drilled during IODP expeditions are described. Local stress estimations from well data (previous block) are shown to make it possible to understand directions and magnitudes of principal stresses in the whole region. Moreover, evaluations of stress state at regional scale based on well data obtained through IODP expeditions are in quantitative agreement with information obtained from historic earthquakes within World Stress Map Project. The reconstructions of stress state in the region reported in the study provide a possibility to predict mechanisms and positions of earthquakes that may occur within the studied subduction zone.
The study provides on overview of some recent advancements in establishing the interconnection between activity of fractures and faults and evolution of stress state of rock mass at different scales with an emphasis on studying these two factors simultaneously. The reported findings and developed techniques can be implemented in scientific earthquake forecasting methods.
In the first block, the study presents some results of laboratory experiments devoted to predict initiation and propagation of new fractures as well as activation of pre-existing fractures in rock samples subjected to varied loading. Stress vs. strain loading curves obtained from triaxial loading tests are interpreted using non-associated plastic flow law, energy release concept, and brittleness evaluation methods to predict spatial orientations, positions, and effective properties of fractures that become tectonically active at various loading points leading to corresponding changes in the inner structure of the rock. The predictions are consequently checked using analysis of acoustic emission during experiment and detailed studies on rock inner structure using tomography and ultrasonic measurements.
The second block of the study is devoted to relationship between stress state of rock masses and activity of natural fractures that can be analysed through well-logging data. The study presents a modified procedure for evaluating stress state of well surrounding masses based on fluid conductivity of natural fractures existing in it. Two recent results of evaluating stress via this method are presented for specific regions related to subduction zones: Hikurangi Subduction Zone (New Zealand) and Nankai Trough Subduction Zone (Japan). Both regions are characterized with presence of wells with enough logging data to deal with conductivity of natural fractures in well surrounding rock masses, so that stress state can be evaluated. Activity of natural fractures is shown to be a reliable method of stress evaluation via comparing the results with stress estimations performed with conventional methods where possible.
The third block of the study directly broadens the previous scale to regional scale. Recent results of analysing stress state of Nankai Trough Seismogenic Zone from discrete data from wells drilled during IODP expeditions are described. Local stress estimations from well data (previous block) are shown to make it possible to understand directions and magnitudes of principal stresses in the whole region. Moreover, evaluations of stress state at regional scale based on well data obtained through IODP expeditions are in quantitative agreement with information obtained from historic earthquakes within World Stress Map Project. The reconstructions of stress state in the region reported in the study provide a possibility to predict mechanisms and positions of earthquakes that may occur within the studied subduction zone.
The study provides on overview of some recent advancements in establishing the interconnection between activity of fractures and faults and evolution of stress state of rock mass at different scales with an emphasis on studying these two factors simultaneously. The reported findings and developed techniques can be implemented in scientific earthquake forecasting methods.