Unconventional Reservoirs: Mathematical Modeling of Some Non-linear Problems

Date
2014-09-02
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Abstract
The decline in conventional hydrocarbon resources coupled with the increase in energy demand has encouraged the development of unconventional resources such as gas-hydrate reservoirs and shale/tight formations. The understanding and analysis of the factors that affect the performance of these reservoirs are critical for their efficient exploitation. Mathematical models are widely used to analyse conventional reservoirs. However, development of such models for unconventional reservoirs is complex, due to the non-linearity of the governing equations. These non-linearities may originate from different sources such as: phase change due to hydrate dissociation in gas-hydrate reservoirs, pressure dependence of permeability, variable gas compressibility, saturation changes during two-phase flow, to name a few. The main objective of this work is to develop some mathematical models for these unconventional reservoirs. The focus will be on two specific types of unconventional resources; namely (1) gas-hydrate reservoirs and (2) tight formations. In the first part of this study, the various governing equations of fluid flow, heat transfer, thermodynamics and kinetics of hydrate decomposition, which are all integral to gas production from hydrate reservoirs, are solved simultaneously to develop two predictive models to forecast the performance of flat and tilted hydrate reservoirs. Furthermore, a material balance equation was developed for hydrate-capped gas reservoir. For this purpose, an effective gas deviation factor, Z*, analogous to Z, was defined such that the traditional p/Z analysis technique could be used to estimate OGIP from production data. In the second part of this study, a methodology was developed for modeling the non-linear diffusivity equations. Rather than using a distance of investigation equation, which can be problematic in complex flow geometries, a “volume of investigation” was used. The applicability of this technique for stress-sensitive formations and tight/shale gas reservoirs was explored through a new implementation of pseudotime. The solution developed is valid during transient, boundary-affected and boundary-dominated flow. Moreover, a theoretical basis was established to understand the behavior of tight oil reservoirs during the transient flow period, including the effect of saturation and relative permeability changes, and the highly non-linear two-phase flow equations were analyzed and solved analytically.
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Keywords
Engineering--Petroleum
Citation
Tabatabaie, S. H. (2014). Unconventional Reservoirs: Mathematical Modeling of Some Non-linear Problems (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/28553