Abstract
The presence of water, i.e., connate or hydraulic fracturing water, along with the gaseous hydrocarbons in shale nanopores is largely overlooked by previous studies. In this work, a new unified real gas-transport model has been developed for both organic and inorganic porous media accounting for the nanoconfined water film flow. More specifically, a gas core flows in the center of the organic/inorganic pore surrounded by a water film which can be further divided into an interfacial region (near-wall water) and bulk region (bulk water). We differentiate the varying water viscosity between the two regions and consider disparate slip boundaries; that is, the near-wall water can slip along the hydrophobic organic pore surface while it is negligible in hydrophilic inorganic pores. Incorporating modified boundary conditions into the Navier-Stokes equations, gas transport model through single organic/inorganic pore is derived. The model is also comprehensively scaled up to the porous media scale considering the porosity, tortuosity, and total organic carbon (TOC) contents. Results indicate that the gas flow capacity decreases in moist conditions with mobile or nonmobile water film. A mobile water film, however, compensates its negative effect up to 50% by enhancing gas flow compared with static water molecules. The real gas flow is dominated by the gas slippage and water film mobility which are dependent upon pore-scale parameters such as pore sizes, topology, pressure, and surface wettability. Compared with inorganic pores, gas transport in organic pores is greatly enhanced by the water film flow due to the strong water slip. Moreover, the contribution of water film mobility is remarkable in small pores with large contact angles, especially at high pressures. At moist conditions, the real gas effect enhances gas flow by improving both gas slippage and water film mobility, which is more prominent in smaller pores at high pressures. The presented model and its results will further advance our understanding of the mechanisms responsible for the water and gas transport in nanoporous media, and consequently, the hydrocarbon exploration of shale reservoirs.
Highlights
Shale gas, which predominantly consists of methane, plays an increasingly important role in global gas production due to its low emissions, high energy efficiency, and abundant reserves in the world [1]
A new model of the real gas transport in both organic and inorganic nanopores has been developed which takes into account, for the first time in literature, an important porelevel physics, i.e., the nanoconfined water film flow, in shales under reservoir conditions
If the water film is mobile, the film compensates its negative effect by increasing the gas flow up to 50% compared to the stagnant water film situations
Summary
Shale gas, which predominantly consists of methane, plays an increasingly important role in global gas production due to its low emissions, high energy efficiency, and abundant reserves in the world [1]. Sun et al [36] established an analytical model for the conductance of confined water in the nanopores They pointed out that the interaction between pore surface and fluid molecules plays a key role in the flow of water, especially for the nano-sized pores. The volume size of the gas molecule is nearly comparable to the scale of the nanopores, and it cannot be treated as a point [39, 41, 42] Both of the factors are named as a real gas effect, which needs to be considered in order to accurately quantify the gas transport through shale porous media under reservoir conditions. The AGP evolution at variable boundary conditions, the sensitivity of impact factors, and the contributions of gas slippage and water film mobility to gas flow in the new unified gastransport model are implemented
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
