Simulation of the hydraulic fracture process in two dimensions using a discrete element method

We introduce a discrete element simulation for the hydraulic fracture process in a petroleum well which takes into account the elastic behavior of the rock and the Mohr-Coulomb fracture criterium. The rock is modeled as an array of Voronoi polygons joined by elastic beams, which are submitted to tectonical stresses and the hydrostatic pressure of the fracturing fluid. The fluid pressure is treated like that of a hydraulic column. The simulation reproduces well the time and dimensions of real fracture processes. We also include an analysis of the fracturing fluid loss due to the permeability of the rock which is useful in an efficiency analysis of the treatment. The model is a first step for future applications in the petroleum industry

Axisymmetric column collapses of bi-frictional granular mixtures

The behavior of granular column collapses is associated with the dynamics of geohazards, such as debris flows, landslides, and pyroclastic flows, yet its underlying physics is still not well understood. In this paper, we explore granular column collapses using the spheropolyhedral discrete element method (DEM), where the system contains two types of particles with different frictional properties. We impose three different mixing ratios and multiple different particle frictional coefficients, which lead to different run-out distances and deposition heights. Based on our previous work and a simple mixture theory, we propose a new effective initial aspect ratio for the bi-frictional granular mixture, which helps unify the description of the relative run-out distances. We analyze the kinematics of bi-frictional granular column collapses and find that deviations from classical power-law scaling in both the dimensionless terminal time and the dimensionless time when the system reaches the maximum kinetic energy may result from differences in the initial solid fraction and initial structures. To clarify the influence of initial states, we further decrease the initial solid fraction of granular column collapses, and propose a trial function to quantitatively describe its influence. Due to the utilization of a simple mixture theory of contact occurrence probability, this study can be associated with the friction-dependent rheology of granular systems and friction-induced granular segregations, and further generalized into applications with multiple species of particles in various natural and engineering mixtures

Mesoscopic approach to fluid-solid interaction: Apparent liquid slippage and its effect on permeability estimation

The liquid slippage behavior due to molecular interactions at fluid-solid (F-S) interfaces is of great importance to the transport of shale oil and clay water. A mesoscopic single-phase lattice Boltzmann method (LBM), based on a continuous and exponentially decaying F-S interaction force and a midgrid bounce-back boundary condition, is proposed to be responsible for the apparent liquid slippage. The F-S interaction force is established at the particle level and thus can be readily extended to porous media. When it is repulsive (attractive), the phenomena of positive (negative) slip lengths and fluid slip (damping) are successfully recovered. This model is validated by the velocity profiles on hydrophobic and hydrophilic surfaces in a benchmark microchannel flow experiment. The slip length is found to be independent of shear rate (its constituents including body force, pore diameter, and kinematic viscosity), but dependent on pore geometry (smaller in porous media than in capillary tubes). Both slip length and permeability ratio follow a power law relationship with interaction parameters (strength and decay length) in capillary tubes and porous media. The permeability ratio estimated analytically with the slip length considered agrees well with that calculated from the LBM simulations, except for the fluid slip in porous media with a significant overestimation. The estimated permeability ratio indicates that it increases (decreases) nonlinearly as the pore diameter decreases, suggesting the great importance of the F-S interaction particularly for thin capillary tubes and microporous media

Determination of thermal conductivity of soil using standard cone penetration test

The thermal cone dissipation test is a newly-developed method for determining thermal conductivity in situ based on temperature dissipation over time. The standard cone penetration test with pore pressure measurement (CPTu) is used. The cone heats up as it is pushed through the soil, due to the build-up of friction on the cone and rods. The dissipation of this heat can then be measured when penetration of the cone is stopped at intervals, and the thermal conductivity of the soil over that test interval determined. Three thermal cone dissipation tests (TCT) were conducted, the first test in soft clay with a high moisture content, and the second and third tests in clay containing a stiff sandy clay layer. The stiff sandy clay layer showed the more significant temperature increase on cone penetration. Using a previously developed correlation, the thermal conductivity was then calculated for each TCT. The temperature increase of the cone for the duration of each CPTu test was also recorded. While the TCT is a promising new test, it is suggested that further research is necessary to develop and refine the method

Enzymatic preparation of structured triacylglycerides containing γ-linolenic acid

with the addition of molecular sieves (MS) at different addition times (3, 9, 12 and 15 h) and loads (2.5, 5, 10 and 15%, based on the total weight of substrates), the enrichment of GLA from evening primrose oil (EPO) and 1- butanol (BtOH) was improved via Candida rugosa lipase-catalysed esterification reactions. Secondly, the GLAenriched fraction was separated by thin-layer chromatography (TLC) to be further set to react during the third step in the presence of glycerol and Candida antarctica fraction B (CALB), under different enzyme loadings (5, 10, 15 and 20%, based on the total weight of substrates), temperatures (30, 40, 50 and 60 ◦C) and substrates molar ratios (1:1, 2:1, 3:1 and 4:1, GLA:glycerol). 60% of STAG containing 49 wt% of GLA were produced by using 15% of CALB at 60 ◦C and a 3:1 molar ratio.Conacyt: Beca no. 328716 UAEMex: Proyecto 3866/2015/PI

A lattice Boltzmann investigation of steady-state fluid distribution, capillary pressure and relative permeability of a porous medium: Effects of fluid and geometrical properties

Simulations of simultaneous steady-state two-phase flow in the capillary force-dominated regime were conducted using the state-of-the-art Shan–Chen multi-component lattice Boltzmann model (SCMC-LBM) based on two-dimensional porous media. We focused on analyzing the fluid distribution (i.e., WP fluid-solid, NP fluid-solid and fluid-fluid interfacial areas) as well as the capillary pressure versus saturation curve which was affected by fluid and geometrical properties (i.e., wettability, adhesive strength, pore size distribution and specific surface area). How these properties influenced the relative permeability versus saturation relation through apparent effective permeability and threshold pressure gradient was also explored. The SCMC-LBM simulations showed that, a thin WP fluid film formed around the solid surface due to the adhesive fluid-solid interaction, resulting in discrete WP fluid distributions and reduction of the WP fluid mobility. Also, the adhesive interaction provided another source of capillary pressure in addition to capillary force, which, however, did not affect the mobility of the NP fluid. The film fluid effect could be enhanced by large adhesive strength and fine pores in heterogeneous porous media. In the steady-state infiltration, not only the NP fluid but also the WP fluid were subjected to the capillary resistance. The capillary pressure effect could be alleviated by decreased wettability, large average pore radius and improved fluid connectivity in heterogeneous porous media. The present work based on the SCMC-LBM investigations elucidated the role of film fluid as well as capillary pressure in the two-phase flow system. The findings have implications for ways to improve the macroscopic flow equation based on balance of force for the steady-state infiltration