William Dershowitz

Dual porosity fracture flow and transport

In rock masses where fracture flow greatly exceeds flow through the rock matrix, the matrix provides a storage porosity which needs to be considered for transient flow, and for solute transport. This paper presents a dual-porosity, single permeability approach for evaluation of flow and transport in fractured rock. The fracture network flow approach is based on a generic matrix block similar to the method of Warren and Root (1963), applied to realistic fracture geometries. The solute transport approach is based on a probabilistic concept of matrix diffusion as a process of Brownian motion, implemented using a probabilistic particle tracking technique.

Analysis of heterogeneously connected rock masses by forward modeling of fractional dimension flow behavior

Abstract The dimension of a well test indicates how conductance (the product of hydraulic conductivity and flow area) changes with distance from a pumping well. Dimensional information is very important because it is one of the few direct hydraulic measures of rock mass heterogeneity and connectivity. Although a relationship between flow geometry and well test dimension has long been hypothesized, little work has been done to evaluate this relationship, much less use it in practical fracture-flow problems. This paper provides examples of the variability of flow dimension in well test data sets from Swedish and Japanese experimental sites. The paper presents an approach which directly determines the dimension of a simulated fracture network, as observed from any point in the network. The approach uses a graph search algorithm to identify the connected portion of the network and calculate the distance-conductance relationships. These relationships translate directly into flow dimension.

Rapid Discrete Fracture Analysis of Hydraulic Fracture Development in Naturally Fractured Reservoirs

Hydraulic fracture simulation is essential to safe, efficient, and productive development of many unconventional resources, including shale gas and oil, tight sands, and increasingly, even fractured carbonates. Hydraulic fracture propagation geometry, and the geometry of both inflated and reactivated (sheared) natural fractures, can be difficult to predict due to their complex interaction with the natural faults and fractures, the mechanical properties of surrounding formations, and the in situ stress field. This paper presents a Discrete Fracture Network (DFN) algorithm, which provides a full, three dimensional assessment of hydraulic fracture and reactivated natural fracture geometry, including both the interaction with the pre-existing geologic setting, and also the interactions which occur between adjacent or simultaneous hydraulic fractures. This approach is rapid, flexible, and convenient, and can be used directly for hydraulic fracture design, resource assessment, and permitting. The approach is limited by the use of semi-empirical algorithms. However, these algorithms can be tuned and verified based on calibration to in situ measurements from production, microseismic imaging, and tomographic fracture imaging. In addition, the algorithms can be refined by comparison to more computationally intensive distinct element simulation methods. Introduction Unconventional oil and gas resources frequently stimulated through large scale hydraulic fracturing. These induced hydraulic fractures provide permeable, connected pathways to deliver oil and gas to production wells, and can dramatically increase improve reservoir economics. Hydraulic fracturing add permeable flow pathways and connected surface areas corresponding to both the induced hydraulic fracture, and in some reservoirs, also inflated and reactivated (“critically stressed”) natural fractures. It is widely accepted and has been proven that natural fracturing heavily influences hydraulic stimulation characteristics (Olson 2010). It follows that an understanding of natural fracturing surrounding the treatment zone, and in the interval between this zone and a potential geohazard, is extremely important to allow assessment of hydraulic fracture characteristics. The Discrete Fracture Network (DFN) approach (Dershowitz et al. 1996) is a proven method in characterising the three dimensional spatial pattern of the fracturing existing within a naturally fractured reservoir. Rogers et al. (2010) describes a Discrete Fracture Network (DFN) approach to better understand the geometry, connectivity, and hydraulic properties of induced hydraulic fractures, and inflated and reactivated natural fractures, and how they influence reservoir production. The DFN Approach has the advantage that it realistically represents discrete fractures, stratigraphy, and geomechanics using a combined continuum and discrete feature approach, which provides a more geomechanically realistic basis for analysis. A typical DFN model for a fractured rock formation is given in Figure 1. URTeC 2013 Page 2341

Hydrogeological investigations: Data and information management

Abstract Hydrogeology is a discipline that may be applied to environmental investigations at wastedisposal sites. The information objectives from such investigations are diverse, and necessitate the development of a variety of data types. Presented herein is an explanation of the logic inherent in the development of data-management system, illustrating how data systems may be developed and managed using generally available software. Current developments in software are discussed and presented in historical context.

Aperture controlled grouting – benefits of the discrete fracture network approach

Fractured rocks, specifically sedimentary sequences, present a particular challenge for grouting, as major connected fractures that must be sealed will rarely be intersected by vertical groutholes. The aperture controlled grouting (ACG) method can be readily applied using discrete fracture network (DFN) analysis approaches to understand the pattern of fractures that need to be grouted. Aperture controlled grouting then utilises a combination of the principles of fracture grouting and grouting intensity number (GIN) grouting for practical and cost-effective grouting of tunnel, dam, shaft, or environmental restoration projects. This paper illustrates the application of DFN techniques for fracture assessment for grouting design and then compares the ACG approach to more conventional grouting approaches based on recent grouting experience.

Discrete Feature Approach for Heterogeneous Reservoir Production Enhancement

The report presents summaries of technology development for discrete feature modeling in support of the improved oil recovery (IOR) for heterogeneous reservoirs. In addition, the report describes the demonstration of these technologies at project study sites.

Fractured reservoir discrete feature network technologies. Final report, March 7, 1996 to September 30, 1998

This report summarizes research conducted for the Fractured Reservoir Discrete Feature Network Technologies Project. The five areas studied are development of hierarchical fracture models; fractured reservoir compartmentalization, block size, and tributary volume analysis; development and demonstration of fractured reservoir discrete feature data analysis tools; development of tools for data integration and reservoir simulation through application of discrete feature network technologies for tertiary oil production; quantitative evaluation of the economic value of this analysis approach.