Abstract
The oil recovery factor from shale oil remains low, about 5 to 7% of the oil in place. How to increase oil recovery from shale oil reservoirs is attracting more and more attention. CO2 huff-and-puff was historically considered one of the best approaches to improve the oil rate. Most previous simulation studies have been based on dual porosity, but simulation results from dual-porosity models have not been as accurate as discrete fracture models in composition modeling. This study proposes a new model that integrates the embedded discrete fracture model and the dual-porosity, dual-permeability model (DPDP). The newly developed method could explicitly describe large-scale fractures as flow conduits by embedded discrete fracture modeling and could model the flow in small- and medium-length fractures by DPDP modeling. In this paper, we first introduce four different non-neighboring connections and the way to calculate the transmissibility among different media in the new model. Then, the paper compares the performance of the new method, discrete fracture modeling, DPDP modeling, and embedded discrete fracture modeling for production from oil reservoirs. Following, the paper carries out a series of simulations to analyze the effects of hydraulic fracture stages, hydraulic fracture permeabilities, and natural fracture permeabilities on the CO2 huff-and-puff process based on the new method. In addition, the injection cycle and soaking time are investigated to optimize CO2 huff-and-puff performance. This study is the first to integrate embedded discrete fracture modeling with DPDP modeling to simulate the CO2 huff-and-puff process in a shale oil reservoir with natural fractures. This paper also provides detailed discussions and comparisons on the integrated strategy, embedded discrete fracture modeling, discrete fracture modeling, and dual-porosity, dual-permeability modeling in the context of fracture simulation with a compositional model. Most importantly, this study answers the question regarding how fractures affect CO2 huff-and-puff and how to optimize the CO2 huff-and-puff process in a reservoir with natural fractures.
Highlights
Complex fracture networks in shale oil reservoirs make the accurate modeling of oil production in these reservoirs very challenging
In order to balance accuracy, computational efficiency, and field practice, we propose a new method that integrates embedded discrete fracture models (EDFMs) and dual-porosity, dual-permeability (DPDP) concepts to model the production process in shale oil reservoirs
Small matrix rock”matrix properties, are obtained by upscaling methods. This way, theThis smallway, and the medium and medium fractures are deducted from the EDFM, resulting in a big reduction in the simulation and medium fractures are deducted from the EDFM, resulting in a big reduction in the simulation fractures effort. are deducted from the EDFM, resulting in a big reduction in the simulation effort
Summary
Complex fracture networks in shale oil reservoirs make the accurate modeling of oil production in these reservoirs very challenging. The DFM method, in which an element and a control volume explicitly represents each fracture by, was established to model fluid flow in individual fractures and provide more realistic representations of fractured reservoirs than dual-continuum models. Monteagudo and Firoozabadi [12] and Matthäi and Belayneh [13] used control-volume finite element methods for multiphase flow in fractured media and developed numerical simulators. Karimi-Fard et al [14] extended DFMs compatible with multiphase reservoir simulators based on an unstructured control-volume finite difference formulation. In order to balance accuracy, computational efficiency, and field practice, we propose a new method that integrates EDFM and dual-porosity, dual-permeability (DPDP) concepts to model the production process in shale oil reservoirs. Different engineering factors and injection strategies are analyzed and compared to provide guidance for production optimization during the CO2 huff-and-puff process
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