A Strain Rate Dependent Constitutive Model for the Lower Silurian Longmaxi Formation Shale in the Fuling Gas Field of the Sichuan Basin, China

Abstract

Shale, as a kind of brittle rock, often exhibits different nonlinear stress-strain behavior, failure and timedependent behavior under different strain rates. To capture these features, this work conducted triaxial compression tests under axial strain rates ranging from 5×10 −6 s −1 to 1×10 −3 s −1 . The results show that both elastic modulus and peak strength have a positive correlation relationship with strain rates. These strain rate-dependent mechanical behaviors of shale are originated from damage growth, which is described by a damage parameter. When axial strain is the same, the damage parameter is positively correlated with strain rate. When strain rate is the same, with an increase of axial strain, the damage parameter decreases firstly from an initial value (about 0.1 to 0.2), soon reaches its minimum (about 0.1), and then increases to an asymptotic value of 0.8. Based on the experimental results, taking yield stress as the cut-off point and considering damage variable evolution, a new measure of micro-mechanical strength is proposed. Based on the Lemaitre's equivalent strain assumption and the new measure of micro-mechanical strength, a statistical strain-rate dependent damage constitutive model for shale that couples physically meaningful model parameters was established. Numerical back-calculations of these triaxial compression tests results demonstrate the ability of the model to reproduce the primary features of the strain rate dependent mechanical behavior of shale.

Constitutive Model for Grouted Rock Mass by Macro-Meso Damage

“…The Lemaitre assumption was proposed by French scholar Roger Lemaitre in 1982. Since then, the Lemaitre assumption has been widely used in the fields of geotechnical engineering and material mechanics [ 44 , 45 , 46 ]. Figure 1 illustrates a rock containing both macroscopic and microscopic defects, a rock containing only macroscopic defects, a rock containing only microscopic defects and a virtual rock without damage at all.…”

Prediction of Shale Gas Pressure based on Multi‐channel Seismic Inversion in Fuling

“…The Baima Block of the Fuling shale gas field is located west of the Qiyueshan Fault and southeast of the Jiaoshiba Block (Hou et al, 2019;Luo et al, 2019;Tang et al, 2019), which is developed in a transition zone of thrust deformation and decollement fold deformation (Fig. 1).…”

Estimation of Fracture Geometry Parameters and Characterization of Rock Mass Structure for the Beishan Area, China

“…Firstly, rock was processed into cylindrical specimens of ϕ 50 mm × 100 mm by cutting machine. The size bias of the specimens was allowed in accordance with the standard requirements of the International Society of Rock Mechanics with the height and diameter controlled within ± 0.3 mm and both ends of the specimen flatness within ± 0.02 mm (Yin et al, 2016;Hou et al, 2019). Then, the uniaxial compression tests were performed on the MTS-815 mechanical testing machine with a maximum load capacity of 1000 kN.…”