DFN Generator v2.0: A new tool to model the growth of large-scale natural fracture networks using fundamental geomechanics

Abstract

Abstract. In this paper we present a new code to build geologically realistic models of natural fracture networks in geological formations, by simulating the processes of fracture nucleation, growth and interaction, based on geomechanical principles and the geological history of the formation. This code implements the fracture modelling algorithm described in Welch et al. (2020), developed to generate more accurate, better constrained models of large fracture networks than current stochastic techniques. It can efficiently build either implicit fracture models, explicit DFNs, or both, across large (km-scale) geological structures such as folds, major faults or salt diapirs. It will thus have applications in engineering and fluid flow modelling, including CO2 sequestration and geothermal energy, as well as in understanding the controls on the evolution of fracture networks. The code is written in C Sharp and is provided with two interfaces: a standalone interface with text file input and output, that can be compiled in standard C Sharp and can run simple models, and a plug-in interface for the Petrel geomodelling package from Schlumberger, that can run more complex models of real geological structures. The standalone version has been used to run extensive sensitivity analyses, which studied the influence of various mechanical and physical parameters (e.g. layer thickness, applied strain, Young’s Modulus, etc.) on the fracture evolution and geometry, by varying the parameters individually in simple models. The Petrel plug-in has been used to evaluate the code applicability by running simulations of actual fractured layers in outcrops and in the subsurface, and comparing the results with observed fracture patterns.

Review of discrete fracture network characterization for geothermal energy extraction

“…Cumulative density distribution plots and calculation of the variation coefficient of fracture spacing provide a more quantitative analysis of the fracture distribution (Aabø et al, 2005). These results have served as inputs into discrete fracture network models that have been then stochastically generated using the new DFN Generator v2.0 now available as a plugin in Petrel (Welch et al, 2022;.…”

“…These carbonate rocks represent excellent analogues for the geothermal and hydrocarbon reservoirs buried in the subsurface (Giuffrida et al, 2020;Smeraglia et al, 2021). In northern Europe, other researchers propose to combine core data, seismic attributes and acoustic/ resistivity images to stochastically generate a DFN afterwards (Aabø et al, 2005;Welch et al, 2022;Smit and Welch, 2023). Of note, once again a holistic approach to a DFN project has been proposed by the geoscience community.…”

“…As a consequence of the exigencies of a sustainable society, a review of the techniques necessary to generate robust flow models in geothermal reservoirs is needed to (i) approximate the anisotropic and heterogeneous nature of geological media, (ii) account for the exponential proliferation of numerical solutions in the last 30 years, and (iii) integrate established and new experimental approaches. The most recent technical approaches incorporate the use of UAV surveys/LiDAR tablets in the field of remote sensing and seismic attributes from the field of geophysics (Aabø et al, 2005;Smeraglia et al, 2021;Welch et al, 2022). These new techniques also need to be integrated with the more traditional ones (structural scanline surveys, fullbore formation microimager logging, acoustic and optical televiewer logs), for reconstruction of the 3D network of fractures.…”

DFN modelling constrained by multiple seismic attributes using the steering pyramid technology

“…Fractures including joints, faults, pressure solution seams, and deformation bands are pervasive in crustal rocks (Welch et al, 2022). These features interconnect to form complex fracture networks that provide crucial storage space for oil and gas reservoirs, as well as important channels for their transportation and exploitation.…”