Lattice Boltzmann Simulation of Fluid Flow in Synthetic Fractures

Abstract

Fractures play an important role in geothermal reservoir engineering as they dominate the fluid flow in the reservoir. Because of this reason determination of fracture permeability is very important to predict the performance of the geothermal reservoir. A fracture is usually assumed as a set of smooth parallel plates separated by a constant width. The absolute permeability of a smooth-walled fracture is related to the fracture aperture using the cubic law. However, the flow characteristics of an actual fracture surface would be quite different, affected by tortuousity and surface roughness. Though several researchers have discussed the effect of friction on flow, a unified methodology for studying flow on a rough fracture surface has not emerged. As experimental methods are expensive and time consuming most of the time numerical methods are used. In this work, we present results of the numerical computations for single phase flow simulations through two-dimensional synthetically created fracture apertures. These synthetic rock fractures are created using different fractal dimensions, anisotropy factors, and mismatch lengths that are obtained from the producing geothermal reservoirs in South Western Turkey. Lattice Boltzmann Method, which is a new computational approach suitable to simulate fluid flow especially in complex geometries, was then used to determine the permeability for different fractures. Regions of high velocity and low velocity flow were identified. The resulting permeability values were less than the ones obtained with the cubic law estimates. It has been found that as the mean aperture-fractal dimension ratio increased permeability increased. Moreover as the anisotropy factor increased permeability decreased with a second order polynomial relationship.

Quantitative Measurements of Fracture Aperture and Directional Roughness from Rock Cores

“…These data can be subsequently used to can be used to approximate the solution to the NavierStokes equations, while accounting for the actual spatial aperture distribution (Auradou et al 2005;Boutt et al 2006;Eker and Akin 2006;Basagaoglu et al 2008). Hence, the influence of the fracture geometry on the flow path tortuosity and fracture transmissivity can be explicitly modeled, which is of interest to: petroleum and geothermal reservoir engineering, environmental remediation activities and underground nuclear waste disposal.…”

Mathematische Methoden in der Geothermie

“…Wegen der meist sehr rauen Bruchoberfläche, reicht diese vereinfachte Betrachtung nicht aus (vgl. [6,22,52]). Unter den Verfahren zur Modellierung petrothermaler Systeme gehören die DFN zu den präzisesten -sie sind aber sehr schwierig zu implementieren.…”

Laboratory Investigation of Flow Paths in 3D Self-Affine Fractures with Lattice Boltzmann Simulations

“…LBM was applied for the permeability prediction of rough-walled fractures through various simulation confining pressure conditions appropriate to mid-crustal depths [35]. The scaling behaviors of transport properties in rough self-affine fractures was studied through the Lattice Boltzmann simulations, showing that anisotropy of the fracture has more influence on the fracture permeability than the fractal dimension and the mean fracture aperture [36]. Dou et al [37] used the LBM to investigate the influence of wettability in a 3D self-affine rough fracture, finding that the wettability has a significant effect on the evolution of effective interfacial areas.…”