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Collaborating Authors
46th U.S. Rock Mechanics/Geomechanics Symposium
Relationship Between Shear Stress And Shear Strain At Post-peak Curves of Rocks Subjected to Direct Shear Tests
Guimin, Zhang (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Yinping, Li (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Chunhe, Yang (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Wenjun, Jing (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences)
1. INTRODUCTION ABSTRACT: Direct shear tests are usually carried out to find the shear strength parameters, and few attention is paid on the post-peak curve. An experimental and theoretical study on the relationship between the shear strength parameters and the post-peak curve were carried out. Analysis on the shear stress-strain curves showed that when normal stresses sn satisfy certain conditions, the post-peak curve is interrelated to the shear strength parameters by (1) tdrop=td-tr=c and (2) ?=arctan(trsn), where tdrop, td, and tr are the shear stress drop, the peak shear stress, and the residual shear stress respectively. Based on the theoretical analysis of above phenomena, an approximate method was proposed by using post-peak curves to obtain shear strength parameters of rocks, and its concrete calculating process was presented. Finally, through further study on the slope of shear stress-strain curves during the shear stress drop, a shear stress-strain constitutive equation for the whole curve was proposed: t= f(e, sn). It implies visually the physical meaning of post-peak curves: the whole dropping course of shear stress is the releasing course of the cohesion. Through direct shear tests, the shear stress-strain curves of rocks are drawn. To calculate the parameters, a shear strength curve is depicted by using the shear strengths td at different normal stresses sn. As a simplification, we use a straight line to replace the shear strength curve, which is the core of Mohr-Coulomb criterion [2, 3, 11, 12], to calculate the cohesion c and the internal friction angle ?. It is now the most frequently used method to compute shear strength parameters, which only employs the shear strength td but focuses rarely on post-peak curves. Study on the post-peak constitutive relation of rocks is the basis of the stability analysis of surrounding rock and the support design of anchor bolt.
ABSTRACT: The process of fluid injection into dense granular media is analyzed using the DEM code PFC2D ® coupled with a pore network scheme. A simple approach to calibrate the microscale parameters to match the permeability of a particle assembly, predicted from the Kozeny-Carman correlation, is first established. The effect of the injection rate on the grain displacement and fluid flow mechanisms is examined. The numerical results illustrate that, as the injection rate increases, the granular medium behaviors change from that of a rigid porous medium to localized failure that leads to development of fluid channels. Existence of the fluid channels is also reflected in the fluid flow patterns. The numerical results are consistent with previous experimental observations of the injection experiments performed in a Hele-Shaw cell. 1. INTRODUCTION Numerical analysis using the DEM code PFC2D ® [1] coupled with a pore network model is conducted in this study to model the fluid injection process in dense granular media. A better understanding of how a dense granular medium responds when fluid is injected into the medium is of great interest to engineering applications such as compensation grouting, environmental remediation and reservoir stimulation in soft formations. Injection experiments performed using aqueous glycerin solutions as the invading fluid and dry Ottawa F110 as the granular material in a Hele-Shaw cell have revealed many interesting features [2, 3]. Four distinct fluid-grain displacement regimes are identified from these injection tests, namely, a simple radial flow regime, an infiltration-dominated regime, a grain displacementdominated regime, and a viscous fingering-dominated regime. As the injection velocity and the invading fluid viscosity increase, the behaviors of fluid flow change from infiltration-governed to infiltrationlimited. Meanwhile, the granular medium response displays a transition from that of a rigid porous medium to fluid-like behaviors characterized by ramified fluidgrain interface morphology.
- Information Technology > Communications > Networks (0.34)
- Information Technology > Mathematics of Computing (0.34)
1. INTRODUCTION ABSTRACT: The Greater Tindilpie (GT) region located in the Patchawarra Trough (South Australia) is proving to be one the premier hydrocarbon producing regions of the Cooper Basin. To date, approximately 0.3 Tcf of condensate-rich gas has been booked as reserve. The development of these reserves and further resource conversion in GT is currently requiring a consistent and sustained approach. The reservoir section, the Early Permian Patchawarra Formation, is comprised of a series of stacked sands, silts, shales and coals deposited in a fluvio-lacustrine environment. Gas is reservoired within tight sands (Perm range: 0.1-10 mD) and silts; with coals and shales providing source and seal. Prediction of gas pay (Porosity >4%; water saturation <70%) has proven difficult in the GT area due to a large variation in the lateral and vertical distribution of channel, point bar and splay sand bodies, resulting from the complex depositional system. This paper reports on a microseismic project that was implemented in the Cowralli Field defining frac geometry in a well described strike-slip stress environment. Uncertainty around the effect of channel body geometry on fracture propagation led to the acquisition of a 3D VSP survey in a nearby field at Nephrite South Field, west of Cowralli, as optimum drainage will be governed by both frac geometry and channel body architecture influencing frac containment. The Greater Tindilpie (GT) region is located within the South Australia portion of the Cooper Basin, Australia’s premier onshore hydrocarbon province (Fig.1). The Cooper Basin hosts 215 gas fields and 145 oil fields at an average well spacing of approximately 400 acres. Currently, 18 trillion cubic feet (Tcf) original gas in place (OGIP) and 1.1 billion barrels original oil in place OOIP) has been booked; with 6 Tcf of gas and 260 million barrels of oil produced since 1969.
- Oceania > Australia > South Australia (1.00)
- Oceania > Australia > Queensland (1.00)
- Research Report (0.49)
- Overview (0.34)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
- Geology > Sedimentary Geology > Depositional Environment > Continental Environment > Fluvial Environment (0.67)
- Geology > Sedimentary Geology > Depositional Environment > Continental Environment > Lacustrine Environment (0.55)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.46)
- Oceania > Australia > South Australia > Cooper Basin > Patchawarra Formation (0.99)
- Oceania > Australia > Queensland > Surat Basin (0.99)
- Oceania > Australia > Queensland > Cooper Basin (0.99)
- (7 more...)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Reserves Evaluation > Estimates of resource in place (1.00)