Fracture Network Characterization Method

Abstract

A method of representing and using fractures in a model of a subterranean reservoir is described including the partitioning the fracture network into a discretely modeled part and a remaining statistically described part from a statistical description of all fractures, the determination of the correlation effects caused by fractures with dimensions exceeding dimension of the local grid cells and the determination of petrophysical properties while allowing for arbitrary distribution of facture orientations, with all three aspects being combinable to improve the modeling of fractures and the simulation of fractured reservoirs.

1 - 18 . (canceled) 
     
     
         19 . A method comprising:
 providing data for a subterranean region that comprises a fracture network;   describing the fracture network by a single statistical description that comprises statistical parameters that are represented by localized random variables according to corresponding probability distribution laws wherein the single statistical description provides for partitioning into a discrete fracture network portion and a remaining portion;   partitioning the single statistical description into portions by determining values for the localized random variables according to the corresponding probability distribution laws wherein the values comprise fracture geometry parameter values and fracture density values; and   for at least one of the portions, determining homogenized fracture property values.   
     
     
         20 . The method of  claim 19  wherein the fracture geometry parameter values comprise length of longest axis of fracture plane values that each describe a length of a longest axis of a fracture plane. 
     
     
         21 . The method of  claim 19  wherein the fracture geometry parameter values comprise aspect ratio values that each describe a ratio between a longest and shortest axis of a fracture. 
     
     
         22 . The method of  claim 19  wherein the fracture geometry parameter values comprise orientation values that each describe an orientation of a fracture. 
     
     
         23 . The method of  claim 22  wherein the orientation values are defined by a statistical description that describes the probability that an axis that is perpendicular to a fracture plane has a given orientation. 
     
     
         24 . The method of  claim 19  wherein the fracture density values comprise values that each describe a number of fractures crossing a given volume. 
     
     
         25 . The method of  claim 19  wherein the fracture density values comprise values that each describe a cumulative length of fractures crossing a given volume. 
     
     
         26 . The method of  claim 19  wherein the fracture density values comprise values that each describe a cumulative surface area of fractures crossing a given volume. 
     
     
         27 . The method of  claim 19  wherein the fracture density values comprise values defined in part by a given volume wherein the given volume corresponds to a grid cell volume of a grid cell of a grid cell model of the subterranean region. 
     
     
         28 . The method of  claim 19  wherein the homogenized fracture property values comprise homogenized fracture aperture property values. 
     
     
         29 . The method of  claim 28  comprising expressing the fracture aperture property values as attributes for each fracture in the remaining portion. 
     
     
         30 . The method of  claim 19  wherein the homogenized fracture property values comprise fracture permeability property values. 
     
     
         31 . The method of  claim 30  comprising expressing the fracture permeability property values as attributes for each fracture in the remaining portion. 
     
     
         32 . The method of  claim 19  comprising
 receiving a query for a value of a localized random variable at a location within the subterranean region, 
 identifying a type of distribution associated with the localized random variable, 
 identifying a cell associated with the location, 
 retrieving distribution information for the type of distribution, 
 based on the distribution information, building the corresponding probability distribution law, and 
 based on the probability distribution law, determining the value for the localized random variable. 
 
     
     
         33 . The method of  claim 19  comprising outputting the homogenized fracture property values to a simulator for simulating flow in the subterranean region. 
     
     
         34 . The method of  claim 33  comprising simulating flow in the subterranean region. 
     
     
         35 . The method of  claim 19  comprising generating a discrete fracture network from one of the portions. 
     
     
         36 . A method comprising:
 providing data for a subterranean region that comprises a fracture network;   describing the fracture network by a statistical description that comprises statistical parameters that are represented by localized random variables according to corresponding probability distribution laws; and   for each grid cell of a grid cell model of the subterranean region,
 obtaining a fracture density as a cumulative surface area of fractures crossing a volume of a cell, 
 from a probability distribution law of fracture length, a probability distribution law of fracture aspect ratio and a threshold minimum length, computing a proportion of the fracture density, in terms of the cumulative surface area of fractures crossing the cell volume and a number of fractures crossing the cell volume, as having fractures of a fracture length in excess of the threshold minimum length, and 
 based on the proportion, determining a density of fractures for implicit representation via the statistical description.