查看更多>>摘要：? 2021 Elsevier LtdThe permeability of shale is a controlling factor in fluid flow, solute transport, and overpressure development in a sedimentary basin. However, shale permeabilities measured with different fluids can be very different. To investigate and characterize the effects of fluid-rock interactions on shale permeability, a series of flow experiments on three samples collected from the Carboniferous formation in the eastern Qaidam Basin, China, with flow directions perpendicular to the bedding plane, were conducted using deionized water, liquid CO2 and 1 mol/L NaCl solution as permeating fluids, respectively. A water permeability model under the influence of fluid-rock interactions was newly derived. The experimental results indicate that for the same sample, the liquid CO2 permeability is the highest permeability measured, followed by that of deionized water, and that the 1 mol/L NaCl solution permeability is the lowest permeability measured. The liquid CO2 flow obeys Darcy's law, showing a constant permeability, with values of 6.90 × 10?19 m2, 3.80 × 10?20 m2 and 1.59 × 10?18 m2. The movement of the deionized water and NaCl solution in these samples deviates from Darcy's law. The relationship between water permeability and pressure gradient follows a power function, with exponents ranging from 0.96 to 3.41 for deionized water and 0.34–3.30 for NaCl solution. The permeabilities measured with these two fluids exhibit nearly identical ranges (10?20–10?21 m2), but the sample permeated with NaCl solution generally shows a lower permeability under the same pressure gradient. The permeability reduction magnitude between the three liquid permeabilities and the helium absolute permeability was used to represent the fluid-rock interactions strength (FRIS). The FRIS is 0.25–0.96 for liquid CO2, 1.44–2.32 for deionized water and 1.89–3.09 for NaCl solution. The relations between the FRIS and mineral compositions and pore structure of shale samples indicate that the FRIS has a better correlation with the specific surface area and porosity.
查看更多>>摘要：? 2021 Elsevier LtdThis study aims to achieve dust control from the source, reduce the dust concentration of coal mining faces, and provide a safe and pollution-free working environment for underground operators. In this study, dodecyl polyglucoside was used as the matrix material, tris-benzoic acid was used as the crosslinking agent, and eramidopropyl was used as the graft. A new carboxylic anionic surfactant (CAS) was prepared by esterification and amidation crosslinking reactions, nano sodium carboxymethyl cellulose was a micellar accelerator, and a new type of anionic fracturing fluid was prepared. The reaction process and structure of the product were analyzed by infrared spectroscopy, X-ray diffraction and scanning electron microscopy, and the thermal stability of the product was analyzed by thermogravimetry experiments. Related performance testing experiments showed that CAS had a relatively low surface tension, and the product had a relatively high shear viscosity and low filtration. Compared with water and carboxymethyl guar gum fracturing fluid, the product has a better wetting and softening effect on coal. In addition, through molecular dynamics simulation, it is determined that CAS in the product can form a good connection with coal molecules and act firmly on the surface of coal, which greatly promotes the wetting of coal.
查看更多>>摘要：? 2021 Elsevier LtdThe rock-cutting mechanism and force prediction model of disc cutter considering the effect of dense core are proposed in this study. According to the working characteristics of disc cutter and rock breakage theory, the contribution of dense core in the complex process of rock-cutting by disc cutter is investigated in detail. Based on the Mohr-Coulomb failure criterion of the rock, a theoretical analytical expression of dense core length is derived, and a cutting mechanics model of constant cross-section (CCS) type disc cutter is established; thus, the quantitative relationship between normal force and rolling force of a disc cutter and rock mechanical characteristics, cutter geometric parameters and cutting parameters is obtained. This model incorporates the size of a dense core. A rich full-scale linear cutting machine (LCM) database is developed from the literature and the theoretical force is compared with the experimental force. The results show that the proposed theoretical model can accurately predict 93% of the average disc cutter force acting on the rock uniaxial compressive strength (UCS) ranging from 8.4 to 355.6 MPa. As the rock UCS increases, the model prediction ability is significantly improved. In addition, the results comparison and performance evaluation between the proposed model and existing classical models prove that the proposed model is reasonable and reliable. Finally, the effects of model parameters (penetration, rock compressive strength, cohesion, internal friction angle and blade angle) on forces and efficiency of rock-cutting by disc cutter are also discussed. The results illustrate that the rock breakage regularity of disc cutter obtained based on theoretical model is consistent with that of actual engineering. The developed force prediction model for CCS-type disc cutter is a very practical tool for engineers in TBM excavation project.
查看更多>>摘要：? 2022 Elsevier LtdSand production can occur during hydrocarbon production, which poses a significant issue for continued oil and gas production. The existing finite element simulation of sand production usually assumes that the formation rock is a homogeneous medium. However, the actual formation is usually a heterogeneous natural material; during the testing and production process, sand production is a long-term, continuous, and gradual process. The wellbore pressure change has an important influence on sand production. Therefore, this study presents a numerical simulation method for progressive sand production in inhomogeneous formations. First, based on the theory of elastic damage mechanics, considering the heterogeneous characteristics of formation rock physical properties and mechanical parameters, a steady-state coupled hydraulic-mechanical-damage finite element model was established. Second, a multi-layer finite element method with multiple iterations was used to solve the model. After each iteration, the material mechanical parameters were updated to simulate the damage unit equivalent, which simulated the progressive sand production process. Finally, sand production during testing in typical igneous formations was analyzed, the influences of heterogeneity, progressive failure process, and wellbore pressure change are discussed in terms of progressive sand production, and systematic parametric simulation and analysis were conducted. The results show that the sand production zone is controlled by the formation rock heterogeneity and progressive failure process. The results indicate that the sensitivity of the normalized yield zone area (NYZA) to mean parameter value can be ranked as follows: cohesion > Poisson's ratio > Young's modulus > internal friction angle, and the sensitivity of the NYZA to standard of deviation parameter value can be ranked as follows: internal friction angle > Poisson's ratio > Young's modulus > cohesion.
查看更多>>摘要：? 2022 Elsevier LtdDuring blasting excavation of jointed rock slopes, the rock masses of the slopes often suffer an abrupt change in displacement, which is called displacement mutation. This kind of displacement mutation seriously threatens the stability of jointed rock slopes. Taking the left-bank spandrel groove slope in the Baihetan hydropower station as an example, the displacement behaviour of the jointed rock slope under excavation was surveyed based on the field monitoring. It is found that the displacement mutation of the jointed rock slope is closely related to the dynamic disturbances of blasting excavation. Then the numerical simulations based on the FLAC3D program were conducted to study the mechanism and influencing factors of the displacement mutation caused by blasting excavation. The results show that the displacement mutation is attributed to the combined actions of blast loading and transient in-situ stress release occurring on blast-created free surfaces if high in-situ stress exists. Under the compression of blasting pressure and in-situ stress, strain energy is accumulated and stored in the rock masses of slopes. As the blasting pressure decays, the accumulated rock strain energy due to blast loading is rapidly released. Meanwhile, the stored rock strain energy under in-situ stress is also quickly released as blasts create a free surface and the in-situ stress initially exerted on this face is suddenly released over a very short period. It is the rapid release of the rock strain energy that causes joint opening and displacement mutations in jointed rock slopes. Magnitude of the joint opening displacement is positively related to the strain energy release rate. The blasting load at higher peak pressure, longer rise time and shorter fall time and the transient in-situ stress release with a higher initial stress and a shorter period correspond to greater strain energy release rates, and thus will result in larger joint opening displacement.
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