How to Model and Improve Our Understanding of Liquid-Rich Shale Reservoirs with Complex Organic/Inorganic Pore Network
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Copyright 2016, Unconventional Resources Technology Conference (URTeC). New imaging techniques have revealed that the pore networks of shale plays consist primarily of inorganic materials, organic matter and natural fractures. However, the flow mechanism through these multi-porosity systems is not well understood. In addition, liquid-rich shale (LRS) plays exhibit several other challenges to modeling and analysis, including abnormally flattened produced gas-oil ratio (GOR), complex phase behavior and heterogeneous rock properties, etc. In this paper, we report results of our investigations of multiphase flow in LRS plays including the impact of critical parameters related to fluids, rock, pore structure, rock-fluid and stimulation processes on well performance of these resources. We have conducted comprehensive reservoir numerical studies using a new procedure to divide porous media into four different sub-media (porosity systems) with distinctive characteristics: Inorganic material and organic matter in the shale matrix along with natural and hydraulic fractures. New correlations for modifying PVT properties in nano-pores have been used to incorporate the impact of nano-pore confinement on phase behavior in organic nano-pores. The impact of the stimulation process on the formation and creation of the stimulated reservoir volume (SRV) is incorporated into the simulation model by changing natural fracture permeability in varying degrees depending on the distance from the main hydraulic fracture. The impact of rock compaction on transfer properties is captured by using pressure-dependent permeability throughout the natural fractures. The current model gives us the capability to better analyze the complex pore network and the governing flow mechanisms in LRS reservoirs. Different relative permeabilities for organic matter and inorganic materials are employed in our model to account for high critical gas saturations. Our model can also handle various flow interactions between organic matter, inorganic materials and fractures. We concluded that the connectivity between the four pore systems and relative permeability functions are the most important uncertainties that affect fluid flows. Our numerical model reproduced anomalous GORs that have been observed in liquid-rich shale oil wells. The study showed that nano-pore confinement delayed development of two-phase flow. It did not have a significant effect on producing GOR behavior of low thermal maturity reservoirs while in high maturity reservoirs it causes the flat GORs observed in early stages of production. Enhanced critical gas saturation delays mobilization of gas molecules in nano-pores and could extend non-intuitive GOR behavior further when reservoir pressure drops below the bubble point. We found that permeability reduction due to compaction has a significant impact on the performance of LRS wells and could change ultimate oil recovery by more than 5%. Simulation results revealed that hydrocarbon production from LRS reservoirs exhibits complex dynamics that are controlled by the pore network, thermal maturity level, volatility of the reservoir fluid and hydraulic fracturing. The study shows that for moderate-GOR oil reservoirs, the constant GOR duration is greater than that for highly volatile oil reservoirs, as well as in reservoirs with a greater percentage of organic matter pores. This study explored several unique phenomena in LRS reservoirs and presents a new methodology to better for improved modeling LRS wells and to estimate ultimate recovery more accurately. The results can be used for reservoir development strategies. Our This methodology enables reservoir engineers to better understand the complicated physics in LRS reservoir performance and provide a working procedure to transfer micro- scale SEM imaging measurements to reservoir scale simulation models.
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Proceedings of the 4th Unconventional Resources Technology Conference
