Abstract
Different from conventional reservoirs, nanoscale pores and fractures are dominant in tight or shale reservoirs. The flow behaviors of hydrocarbons in nanopores (called “confined space”) are more complex than that of bulk spaces. The interaction between liquid hydrocarbons and solid pore wall cannot be neglected. The viscosity formula which is varied with the pore diameter and interaction coefficient of liquids and solids in confined nanopores has been introduced in this paper to describe the interaction effects of hydrocarbons and pore walls. Based on the Navier-Stokes equation, the governing equation considered liquid/solid effect in two dimensions has been established, and approximate theoretical solutions to the governing equations have been achieved after mathematic simplification. By introducing the vortex equation, the complex numerical seepage model has been discretized and solved. Numerical results show that the radial velocity distribution near the solid wall has an obvious change when considering the liquid/solid interaction. The results consist well with that approximate mathematical solution. And when the capillary radius is smaller, the liquid and solid interaction coefficient n is greater. The liquid and solid interaction obviously cannot be neglected in the seepage model if the capillary radius is small than 50 nm when n>0.1. The numerical model has also been further validated by two types of nanopore flow tests: from pore to throat and inversely from throat to pore. There is no big difference in flow regularity of throat to pore model considering when liquid/solid interaction or not, whereas the liquid/solid interaction of pore to throat model totally cannot be overlooked.
Highlights
Unconventional oil and gas are playing an increasingly important role in global energy supply
Radial velocity distribution curves in the capillary radius of 5 μm are showed in Figures 7 and 8
The results and recognitions can be concluded as follows: (1) The seepage behavior in confined nanopores is different from bulk space, since the liquid and solid interaction would increase the viscosity of hydrocarbons near the pore wall
Summary
Unconventional oil and gas are playing an increasingly important role in global energy supply. Su et al put forward a method based on a mixed control volume-discontinuous finite element formulation to accurately simulate multiphase flow in fractured shale reservoir. It has solved the problem of discontinuous or near discontinuous behavior of saturation in real oilfield [43]. Previous researches have studied flow behavior in big channel considering the liquid and solid interaction, and many numerical reservoir simulation models in terms of shale or tight oil and gas have been investigated. The force of water molecules in boundary layer which is affected by inner interaction action of water molecules and solid pore wall would influence the viscosity. While on the solid surface where y → ∞, the water viscosity is just normal
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