Characterization of Multi-Scale Discrete Fracture Network Systems in Unconventional Reservoirs Using Dynamic Data

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Development of unconventional tight or shale reservoirs has received much attention in recent years because of the large resource estimates worldwide. Horizontal wells with multi-stage hydraulic fracturing are drilled to enhance reservoir contact area and to achieve economic production rates. This stimulation technique is particularly efficient if hydraulic fractures can connect to sweet spots due to the presence of existing fractures. A tight/shale reservoir can be conceptualized as a dual-medium with two distinct sub-systems: matrix and fracture. The time scales for flow in the two systems differ significantly due to the high contrast in their permeability. The matrix has a very low in-situ permeability, while the fracture is a local discontinuity with a very high permeability. Fractures can be large and localized around the wellbore (e.g., hydraulic fractures) or small and located away from the stimulated zone (e.g., micro fractures). It should be noted that this proposal focuses on in-situ development of shale/tight oil/gas reservoirs, while surface mining of oil shale is not considered. ***The overall objective is to develop a suite of numerical models suitable for (1) simulating multi-phase flow in discrete fractures using finite-element based techniques; (2) capturing the impacts of fractures occurring over different scales; and (3) integrating dynamic data (e.g., flow and pressure measurements) for characterizing fracture networks in a robust history-matching workflow. ***This research proposes a novel integrated approach for analyzing multi-phase flow and fluid distribution in low-permeability porous media, where fracture networks, i.e., hydraulic fractures and micro fractures, are present over multiple scales simultaneously. This research would revolutionize the current practice that focuses predominantly on analytical models, which typically ignore multi-phase effects, and finite-volume/finite-difference simulations, which do not handle the complexities in fracture configuration pertinent to tight/shale reservoirs. This loss of model quality renders the description of fracture systems in numerical simulation incomplete and the inference of fracture characteristics from dynamic data challenging. Many industrial practitioners, who are familiar with the state-of-the-art research in unconventional reservoir development, have expressed the need for more sophisticated approaches to analyze and model these reservoirs. It is expected that computational loads that favor current practice are disappearing with the rapid advances in computing technology, and more computationally-intensive techniques, such as those developed in this proposal, could be implemented in commercial codes in the near future. The outcomes would impact our capability to optimize fracturing design, which is also an important consideration in geothermal energy development.