Investigation of Water Imbibition Behavior in Nanopores in Shale Reservoirs
Date
2021-04-08
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Abstract
Shale gas is emerging as an important source of energy supply worldwide. The economic production of shale gas has become feasible because of the increasing global energy demand and advanced multistage hydraulic fracturing technologies. A huge amount of a fracturing fluid is usually injected into a shale formation during a fracturing process, but only a small fraction of the fracturing fluid can be recovered. The main reason for the low recovery of a fracturing fluid is the spontaneous imbibition of the fracturing water into the shale matrix. The current understanding of the water imbibition behavior in shale is still poor, since a pore network of shales is usually complex and heterogeneous, consisting of abundant nanopores. At such confined conditions, a surface to volume ratio is very large and surface forces dominate over volume forces. Therefore, the characteristics of a solid surface have crucial effects on flow properties, and macroscopic hydrodynamic models are insufficient to be applied to water imbibition behavior in shale. To investigate water imbibition behavior in shale and develop its theoretical models, unique properties should be considered, including the slip behavior, an increased viscosity effect, a dynamic contact angle, and the propagation of precursor films. In this thesis, the dynamics of water flow in a quasi-continuum flow regime are investigated. The mechanisms of friction at a liquid-solid interface are firstly investigated, and a relationship between the friction and the slip velocity is established. Moreover, a theoretical model for the effective viscosity of water in nanopores is proposed based on a molecular kinetic Theory, and the factors that affect the effective viscosity are discussed. Besides, a unified model in a quasi-continuum flow regime is established by inserting the effective viscosity model and a slip length model into the traditional Hagen-Poiseuille model. The impact of the wettability condition on the effective viscosity is investigated. Furthermore, the spreading of precursor films is investigated. A model for water imbibition in nanopores is proposed, considering the propagation of the precursor films ahead of a main meniscus. All the models proposed in this thesis have been validated by experimental and simulation results in the literature. The research results in this thesis can be beneficial to an understanding of the water flow behavior in nanopores and will have many applications in the chemical and petroleum industry.
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Keywords
fracturing fluid, spontaneous imbibition, nanopores
Citation
Zhang, L. (2021). Investigation of Water Imbibition Behavior in Nanopores in Shale Reservoirs (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.