Lattice Boltzmann Simulation of Fluid Flow In Synthetic Fractures

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 a 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 tortuosity 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 2D 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 identifies.  The resulting permeability values were less than the ones obtained with the cubic law estimates.  It has been found that as the fractal dimension and mean aperture - fractal dimension ratio increased permeability increased.  Moreover as the anisotropy factor increased permeability decreased with a second order polynomial relationship. 

 

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