HR: 0800h
AN: H11B-0301    [Abstracts]
TI: Fluid Flow Modeling Through Bed-Confined Fracture Networks in Heterogeneous Layered Rocks
AU: * Molina, C A
EM: cmoli004@fiu.edu
AF: Florida International University, Department of Earth Sciences, Miami, FL 33199 United States
AU: Gross, M R
EM: grossm@fiu.edu
AF: Florida International University, Department of Earth Sciences, Miami, FL 33199 United States
AB: Fractures are discrete features that often serve as preferential pathways for fluid flow, especially in rocks with low matrix permeability. One common fracture network observed in sedimentary rocks consists of an earlier set of systematic joints and a later set of cross joints, that together form a well-connected, ladder-like pattern. The goal of our study is to investigate effects of cross joint attributes such as geometry, orientation, aperture and density on flow through bed-confined fracture networks. The 2-D models calculate volumetric flow under steady state conditions through a fracture network consisting of up to 2600 internal nodes. A large system of equations determines hydraulic head values at fracture intersections and calculates volumetric flow through each fracture segment according to the cubic law. For all scenarios the systematic joints are assigned hydraulic apertures of 0.3 mm, whereas cross joint apertures are varied from 0.001 mm to 0.3 mm. A rotation of 0ø corresponds to a hydraulic gradient parallel to the systematic joints. We first investigate cross joints with a uniform fracture spacing ratio (FSR) of 1:1 and an angle between the two fracture sets of 90ø. Upon rotating the fracture network at 5ø increments, the volumetric flow rate (Q) remains approximately constant (~2.3 ml/s) for cross joint apertures of 0.3 mm, implying isotropic behavior for the fracture network. However, using a cross joint aperture of 0.15 mm reduces Q to 1.9 ml/s for 0ø rotation, and a more dramatic reduction to 0.4 ml/s at 90ø rotation where the gradient is parallel to the cross joint trend. Thus, flow is highly anisotropic in the likely event of smaller cross joint apertures. We next investigate effects of cross joint density by varying the spacing of cross joints for rotations of 0ø and 90ø. When flow is parallel to the systematic joints, the cross joint spacing has only a minor effect on flow rate. However, when the flow direction is perpendicular to the systematic joints, high cross joint densities (FSR>3) can result in a five-fold increase in Q. Fracture connectivity in the shallow subsurface is greatly enhanced by the presence of cross joints. Our sensitivity analysis provides constraints on how cross joints influence flow in fractured rocks, which may prove useful in the characterization of heterogeneous formations.
DE: 8010 Fractures and faults
DE: 5104 Fracture and flow
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1869 Stochastic processes
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting