Inverse Fracture Model Integrating Fracture Statistics and Well-testing Data

Abstract

Heterogeneity and poor connectivity of fractures make it difficult to characterize fracture networks and predict flow behavior on them. Previous studies have introduced inversion models integrating the observed pressure data to describe flow patterns. However, they could not consider the statistical properties of fractures because the models are based on regular lattice or continuum approaches. A new inverse fracture model, which simultaneously integrates fracture characteristics, fluid flow, and solute transport data, is proposed. Discretization for the fracture-occurrence points makes it possible to incorporate fracture properties in the inversion. Fluid flow is implemented by the cubic law, and a semi-analytical method is used to include the solute transport data due to its efficient performance. The model can interpret the characteristics of the geometry and conductivity between wells within fractured reservoirs, since the inverse fracture network not only has the same fracture characteristics as observed data, but also reproduces the fluid flow and solute transport data. It is demonstrated that the fracture network that is developed makes responses for additional flow and transport predicted within a reasonable error range.

Synthetic fracture network characterization with transdimensional inversion

“…Discrete fracture networks (DFN) are realistic mappings of fracture geometries based on the field observation via a stochastic representation of fracture properties. Individual fracture geometry and fracture network connectivity are among the key parameters for such a realistic representation [Hestir et al, 1998[Hestir et al, , 2001Jang et al, 2008;Frampton and Cvetkovic, 2010;Niven and Deutsch, 2012;Dorn et al, 2013;Li et al, 2014]. DFN models could model flow and transport in fractured media, although the strong reliance on the cubic law makes these simulations very sensitive to aperture estimations [Neuman, 1988[Neuman, , 2005.…”

“…For instance, Mauldon et al [1993] and Datta-Gupta et al [1995] simulated the fracture network via partially connected conductors with equal or variable apertures, aligned to a predefined lattice as a finite element approximation of the fractured system. Other concepts keep the number of fractures fixed while adjusting their hydraulic properties [Le Borgne et al, 2007;Le Goc et al, 2010;Dorn et al, 2013;Klepikova et al, 2014], activating-deactivating fractures [Hestir et al, 1998;Niven and Deutsch, 2012], or solving the problem over the statistical parameters of the DFN but not on the exact geometries [Jang et al, 2008]. [Dorn et al, 2013] suggested that using variable dimension DFN inversion would be a good choice to improve the capabilities of the existing DFN-based inversion techniques.…”

Thermal experiments for fractured rock characterization: theoretical analysis and inverse modeling

“…Very few studies attempt to infer the statistical characteristics of a network, such as fracture density and scaling exponents in distributions of length, orientation and aperture (I. Jang et al, 2008;Y. H. Jang et al, 2013).…”

Reservoir-scale transdimensional fracture network inversion

“…Discrete fracture network models (DFNs) are more realistic representations of the fractured media, where fractures and the rock matrix are modelled separately (Dorn et al, 2013;Jang et al, 2008;Neuman, 2005;Niven and Deutsch, 2012). This separation allows to solve flow and transport problems effectively, limiting these expensive computations to the open fracture space.…”

“…Substituting the complex DFN model with a simplified model has been proven a good solution to this problem. Simplified DFNs limited to a few main fractures were used to interpret hydraulic, tracer and temperature observations in several studies (Le Borgne et al, 2007;Le Goc et al, 2010;Klepikova et al, 2013Klepikova et al, , 2014. The simplifications made possible the identification and characterization of the preferential flow paths, but could not reconstruct complex fracture patterns.…”