Abstract
Due to its distinct capability to improve the efficiency of shale gas production, supercritical carbon dioxide (SC-CO2) fracturing has attracted increased attention in recent years. Heat transfer occurs in the transportation and fracture processes. To better predict and understand the heat transfer of SC-CO2 near the critical region, numerical simulations focusing on a vertical flow pipe were performed. Various turbulence models and turbulent Prandtl numbers (Prt) were evaluated to capture the heat transfer deterioration (HTD). The simulations show that the turbulent Prandtl number model (TWL model) combined with the Shear Stress Transport (SST) k-ω turbulence model accurately predicts the HTD in the critical region. It was found that Prt has a strong effect on the heat transfer prediction. The HTD occurred under larger heat flux density conditions, and an acceleration process was observed. Gravity also affects the HTD through the linkage of buoyancy, and HTD did not occur under zero-gravity conditions.
Highlights
Shale gas is a type of unconventional natural gas that is found trapped within shale formations.In 2000, shale gas only accounted for 1% of U.S natural gas production, but fifteen years later, it accounted for nearly 50% [1]
More and more studies have argued that hydraulic fracturing may raise a number of environmental problems: (1) a large amount of water is required for one shale gas well [5]; (2) more than 20 types of additives are added in the injection water, such as hydrochloric or muriatic acid, gelling agents, and chemical modifiers, which may contaminate groundwater [6,7]; (3) large-scale water disposal via deep re-injection has been linked to trigger seismicity that results in low-level earthquakes [8,9,10]; (4) other issues include accidental chemical spills, waste disposal, air pollution, and the land footprint of drilling activities [11]
Toselect select appropriate model to predict heat transfer critical region, 56.7 thethe appropriate model to predict thethe heat transfer nearnear the the critical region, the 2 was performed and the comparisons were presented the case with a heat flux density of kW/m case with a heat flux density of 56.7 kW/m was performed and the comparisons were presented in in the Figure was found thatthe theTWL
Summary
In 2000, shale gas only accounted for 1% of U.S natural gas production, but fifteen years later, it accounted for nearly 50% [1]. The boom of shale gas production is mainly due to the wide use of hydraulic fracturing, a well-stimulation technique in which rock is fractured by a pressurized fluid (primarily water containing sand or other proppants suspended with the aid of thickening agents) [2,3,4]. More and more studies have argued that hydraulic fracturing may raise a number of environmental problems: (1) a large amount of water is required for one shale gas well [5];. Economic pressures and environmental targets drive people to use new methods to exploit shale gas. The use of supercritical carbon dioxide (SC-CO2 ) instead of water to drilling and fracture shale has been proposed (Figure 1), whereby liquid
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