Fracture Network Characterization from Borehole Image Logs
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Solution Overview
Problem
Current borehole imaging technologies face challenges in accurately characterizing formation fracture networks within hydrocarbon reservoirs, particularly in determining fracture size, elongation ratio, and rotation angle, which are crucial for assessing reservoir productivity and oil quantity.
Innovation Solution
A method that involves creating a fracture set from borehole image logs, classifying fractures into fully and partially intersecting groups, calculating elongation ratio and rotation angle, and determining the probability of full intersection and fracture size using statistical analysis of intersecting fractures, with specific formulas for calculating the areas of projected fracture ellipses to estimate the probability of full intersection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If borehole imaging is used to capture fracture data, then abundant subsurface data is obtained, but accurate characterization of fracture networks remains challenging
Solution Approach 1:
The fracture set is segmented into two distinct groups: fully intersecting fractures and partially intersecting fractures. This segmentation allows different analytical approaches to be applied to each group, improving the overall characterization accuracy. Fully intersecting fractures provide complete geometric information, while partially intersecting fractures require probabilistic methods to estimate their full geometry.
Solution Approach 2:
The method transitions from 2D borehole image observations to 3D fracture geometry characterization. By using the probability of full intersection and elliptical projection models, the method infers three-dimensional fracture dimensions (area, elongation ratio, rotation angle) from two-dimensional borehole wall intersections, adding a dimensional transformation capability to the analysis.
2Measurement precision
If fracture sets are classified into fully and partially intersecting groups, then fracture geometry can be characterized, but calculation complexity increases
Solution Approach 1:
The method introduces key geometric parameters (elliptical area, elongation ratio, rotation angle) as state variables to describe fracture geometry. By changing the parameter representation from raw image data to standardized geometric descriptors, the complexity of subsequent calculations is reduced while maintaining measurement precision.
Solution Approach 2:
The probability of full intersection (Pfull) serves as an intermediary parameter that bridges the gap between observed borehole intersections and actual fracture geometry. This intermediary allows the method to translate limited borehole observation data into reliable estimates of complete fracture dimensions without requiring direct observation of entire fracture surfaces.
3Measurement precision
If probability of full intersection is determined using elliptical projection area ratio, then fracture size estimation is improved, but computational requirements increase
Solution Approach 1:
The method replaces complex mechanical or iterative optimization approaches with an analytical solution based on elliptical geometry. By using the closed-form formula Pfull = Ai/Ae (where Ai is the intersection area and Ae is the elliptical projection area), the computation avoids time-consuming numerical simulations while maintaining high estimation accuracy.
Data Source
AI summary
Methods may include creating a fracture set from a collection of intersecting fractures in a borehole image log recorded within a subterranean formation; classifying the fracture set into groups of fully and partially intersecting fractures; calculating one or more of the elongation ratio and the rotation angle of the partially intersecting fractures; determining a probability of full intersection of fractures from the fracture set; and determining a fracture size or a parametric distribution of fracture sizes from the fracture set using the calculated one or more of the elongation ratio and the rotation angle and the determined probability of full intersection of formation fractures within the borehole.