Accurate knowledge of the influence of rock deformation on the permeability of fluid flow is of great significance to a variety of engineering applications, such as simultaneous extraction of coal and gas, oil/gas exploitation, CO2 geological sequestration, and underground water conservation. Based on the CT representation of pore structures of sandstones, a LBM(Lattice Boltzmann Method) for simulating CH4 flow in pore spaces at microscale levels and a parallel LBM algorithm for largesize porous models are developed in this paper. The properties of CH4 flow in porous sandstones and the effects of pore structure are investigated using LBM. The simulation is validated by comparing the results with the measured data. In addition, we incorporate LBM and FEM to probe the deformation of microstructures due to applied triaxial forces and its influence on the properties of CH4 flow. It is shown that the proposed method is capable of visually and quantitatively describing the characteristics of microstructure, spatial distribution of flow velocity of CH4,permeability, and the influences of deformation of pore spaces on these quantities as well. It is shown that there is a good consistency between LBM simulation and experimental measurement in terms of the permeability of sandstone with various porosities.
To investigate the relationship between the structural characteristics and seepage flow behavior of rough single rock fractures,a set of single fracture physical models were produced using the WeierstrasseMandelbrot functions to test the seepage flow performance.Six single fractures,with various surface roughnesses characterized by fractal dimensions,were built using COMSOL multiphysics software.The fluid flow behavior through the rough fractures and the influences of the rough surfaces on the fluid flow behavior was then monitored.The numerical simulation indicates that there is a linear relationship between the average flow velocity over the entire flow path and the fractal dimension of the rough surface.It is shown that there is good agreement between the numerical results and the experimental data in terms of the properties a of the fluid flowing through the rough single rock fractures.
Qingang ZhangYang JuWenbo GongLiang ZhangHuafei Sun
To enhance the oil and gas recovery rate, hydraulic fracturing techniques have been widely adopted for stimulation of low-permeability reservoirs. Pioneering work indicates that hydraulic perforation and layout could significantly affect fracture initiation and propagation in low-permeability reservoir rocks subjected to complex in-situ stresses. This paper reports on a novel numerical method that incorporates fracture mechanics principles and the numerical tools FRANC3 D and ANSYS to investigate the three-dimensional initiation and propagation behavior of hydro-fracturing cracks in shale rock. Considering the transverse isotropic property of shale rocks, the mechanical parameters of reservoir rocks attained from laboratory tests were adopted in the simulation. The influence of perforation layouts on the 3D initiation of hydro-fracturing fractures in reservoir rocks under geo-stresses was quantitatively illuminated. The propagation and growth of fractures in three dimensions in different perforating azimuth values were illustrated. The results indicate that: 1) the optimal perforation direction should be parallel to the maximum horizontal principal stress, 2) the crack plane gradually turns toward the direction of the maximum horizontal principal stress when they are not in parallel, 3) compared with the linear and symmetric pattern, the staggered perforation is the optimal one, 4) the proper perforation density is four to six holes per meter, 5) the optimal perforation diameter in this model is 30 mm, and 6) the influence of the perforation depth on the fracture initiation pressure is low.
