--> Abstract: Predicting Fractures and Fluid Flow through Fractures in Basin Modeling, by K. W. Larson, D. W. Waples, H. Fu, and K. Kodama; #91004 (1991)

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Predicting Fractures and Fluid Flow through Fractures in Basin Modeling

LARSON, KURT W., University of Illinois, DOUGLAS W. WAPLES,* Japan National Oil Corporation, HAN FU, Japan Oil Engineering, and KISABURO KODAMA, Geological Survey of Japan

The main value of quantitative 2-D and 3-D basin models for petroleum exploration is their ability to predict expulsion and migration of hydrocarbons on a basin scale. However, existing basin models rely on matrix permeabilities in calculating fluid flow, generally ignoring the contributions of fracture permeability. Fracture permeability may in fact be much larger than matrix permeability, particularly for fine-grained rocks. Wherever significant fracturing occurs, ignoring fracture permeability may cause errors in prediction of groundwater flow rates and directions, caprock permeabilities, migration pathways for hydrocarbons, and thermal history.

We have developed a method that estimates the formation of tectonic fractures during basin simulations. We evaluate the strain between horizontally adjacent nodes and estimate the number of fractures that will occur as a function of rock ductility, fracture orientation, throw on fracture surfaces, and fracture aperture. Our model is capable of considering stresses induced by both block faulting and by concentric folding.

We can calculate fracture-system permeability in two different ways: (1) directly from strain using an empirical calibration, and (2) from consideration of fracture aperture, density, and orientation. Finally, we calculate total permeability as the sum of matrix permeability and porosity-weighted fracture-network permeability.

We simulate diagenetic and tectonic closure of fractures using a first-order decay equation to describe the reduction of fault aperture through time. Predictions of our model have been successfully compared against those of a model based entirely on tectonic stresses.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)