Zhu Weiyao

Dynamic Characteristics of Gas Transport in Nanoporous Media

Special flow mechanism and percolation characteristics for gas transport are presented in nanoporous media, which cannot be explained by the traditional motion equation of Darcys law. On the basis of theoretical analysis, we establish a low velocity nonlinear transfer equation of gas in nanoporous media and a mathematical model of gas volume flow in multi-scale porous media. By utilizing nonlinear numerical calculation methodology, a detailed quantitative analysis of the diffusion and convective rate of gas flow is presented, providing a theoretical foundation for the development of nanoporous media.

Study on the multi-scale nonlinear flow mechanism and model of shale gas

Shale gas reservoirs have extremely complex structures with nano-pores and fractures. And the multiscale flowing states are also existed in it. The gas flowing characteristic is apparently different with normal gas reservoirs. In this paper, gas flow in porous media is was researched studied under different gas flowing state by the Knudsen number and the flowing mechanism, and the characteristics are explained. Then we build a unique general flowing shale gas model with multi-scale, by comprehensively considering Darcy flow, slip flow, diffusive flow and non-Darcy flow with high speed at the bottom hole, which are all the non-linear effects. A new shale gas model with combining original shale and fracturing areas is introduced to calculate the gas productivity by considering settled pressure conditions. The simulative results are calculated by the gas productivity functions and analyzed the sensitivity of parameters with the real productivity. The results show that shale gas productivity would increase by the increasing on the diffusion coefficient, parting coefficient and the radius of fractures, but the increasing rate would have the opposite effect. The productivity with considering non-Darcy effect was a little lower than the result without considering this effect. And the high speed non-Darcy had less effect on gas productivity when comparing with the slippage-diffusion. This model has offered a series of theories for forecasting and optimizing the productivity of shale gas with SRV.

Numerical computation for nonlinear unsteady percolation of shale gas and prediction of production

According to the reality of the marine shale reservoirs in South China, multi-scale gas flow in the shale reservoirs with special pore structure characteristics is considered. By using the Knudsen number, it is judged that the dominant pattern of flow in shale porous media is slip flow, and it is pointed out that the process of gas transport is an isothermal process. On the basis of multiscale Beskok-Karniadakis flow model, the corresponding second-order approximation correction is given and the mathematic model of nonlinear unsteady radial percolation is established for the tight shale gas wells. The problem is simplified by applying the Boltzmann transformation and an explicit iteration scheme to solve the pressure is presented by numerical discrete technique. The distribution curves of pressure with time and space are obtained for the case of the constant pressure at the inner boundary. The variation of output over time is predicted and the influence of desorption, slippage and diffusion on the production is analyzed.

Mathematical Model for Low-Velocity Flow of Coal Bed Methane in Low-Permeability Reservoirs

A mathematical model for transport of coal bed methane(CBM) was presented, taking into account low-velocity non-Darcy flow behavior and coupling of methane desorption from coal matrix and diffusion from matrix into cleats. Under several simplifying assumptions, a simple calculation method for control area of single wells was proposed. Low-velocity non-Darcy flow behavior was characterized by pseudo threshold pressure gradient (PTPG). Numerical results show that both PTPG and desorption rate have a significant impact on determination of control radius. PTPG has a negative effect on the deployment of the peripheral reserves. Increasing PTPG would result in fewer control area. In the contrast, increasing desorption rate would lead to larger control area. The calculation method would provide engineers a better understanding of development of CBM.