AbstractsLaw & Legal Studies

The main challenge of naturally fractured reservoirs (NFRs) is understanding how fractures behave in the subsurface outside the radius of influence of wells. Fractured outcrop analogues provide geological concepts that can be used to extrapolate fracture data outside the well control. Numerous methods for studying fractured outcrops are available but they all have different disadvantages. We propose a new methodology using Digifract 1.0 software that allows for quick digitization of fractures resulting in a statistically significant quantitative dataset. This approach is used in a carbonate quarry in France to digitize height, dip and azimuth of nearly 1800 non-stratabound fractures on vertical outcrop walls, taking into account assumptions and pitfalls that are often overlooked. The 2D height and spatial distributions of two non-stratabound fracture sets identified in the quarry follow power-law distributions. Applying the 2D distributions in FracMan stochastic fracture simulation software results in 3D DFNs that honour the properties of the 2D distributions. The 3D DFNs form percolating clusters of fractures but for the assumed subsurface conditions the fracture networks would not percolate. The maximum fracture size and the dispersion in the orientation distribution have the largest effect on the percolation threshold. Fracture spacing in 3D is very similar to fracture spacing in 2D. There is a significant sampling error in fracture spacing measurements along scanlines that are not perpendicular to the average fracture dip. The most commonly used correction, Terzaghi, corrects for this as long as the angle between the fracture dip and the scanline is larger than 30 degrees. For smaller angles no uniform correction method has been found.