Shales or mudstones are fine grained and layered reservoirs, which leads to strong shale permeability anisotropy. Shale has a wide pore-size distribution, and pores with different diameters contribute differently to the apparent permeability of shales. Therefore, understanding the anisotropy of multiscale shale gas reservoirs is an important aspect to model and evaluate gas production from shales. In this paper, a novel model of permeability anisotropy for shale gas reservoirs is presented to calculate the permeability in an arbitrary direction in three dimensional space. A numerical model which is valid for the entire Knudsen’s range (continuum flow, slip flow, transition flow and free molecular flow) in shale gas reservoirs was developed, and the effect of gas-water flow and the simulation of hydraulic fracturing cracks were taken into consideration as well. The simulation result of the developed model was validated with field data. Effects of critical factors such as permeability anisotropy, relative permeability curves with different nanopore radii and initial water saturation in formation on the gas production rate of multi-stage fractured horizontal well were discussed. Besides, flow regimes of gas flow in shales were classified by Knudsen number, and the effect of various flow regimes on both apparent permeability of shales and then the gas production has been analyzed thoroughly.

Deep fractured tight gas reservoirs have attracted more and more attention worldwide, which also promotes the large‐scale application of oil‐based drilling fluids. Due to its poor permeability, deep tight gas reservoirs need to pay more attention to the issue of reservoir protection. However, previous studies have shown that reservoir damage of oil‐based drilling fluid is small, and limited damage studies mainly focus on one aspect of work, and there is not a systematic reservoir protection method of oil‐based drilling fluid for tight gas reservoir. Based on the particularity of fractured tight gas reservoir protection, the thesis clarifies the fracture factors that affect the reservoir protection efficiency and the preferred factors of reservoir protection materials. Considering fully the characteristics of fracture and oil‐based drilling fluid, the design basis and overall design idea of reservoir protection method of oil‐based drilling fluid are established. Considering the four conditions of fracture determination and method selection, difference of Engineering requirements, particle selection, fracture plugging, and plugging removal mechanism, the reservoir protection technology of oil‐based drilling fluid is constructed, and the simulation experiments of reservoir protection technology of oil‐based drilling fluid for fractured tight gas reservoir were carried out; the results provided a reference for reservoir protection of oil‐based drilling fluid.

Multiflow mechanisms coexist in shale gas reservoirs (SGRs) due to the abundant nanopores and the organic matter as a medium of gas souring and storage. The gas transport mechanisms in nanopores including bulk gas transfer and adsorption‐gas surface diffusion were already investigated in pore‐scale models, but their effects on actual gas production of multistage fractured horizontal wells in SGRs are not clearly understood, which are crucial for the economic development of unconventional resources. Therefore, a comprehensive apparent permeability (AP) model which couples the surface diffusion of adsorbed gas, slippage flow considering the additional flux generated by surface diffusion based on Langmuir's theory, and Knudsen diffusion is established. The presented model is validated with the experimental data and lattice Boltzmann method (LBM) simulation results. Then, we propose a numerical model which combines multiflow mechanisms in microscale pores and a multistage fractured horizontal well (MSFHW) in macroscale shale gas reservoirs together. The effects of different transport mechanisms on both AP of nanopores and gas production are analyzed thoroughly. The results show that the effect of surface diffusion on the apparent permeability of nanopores is much greater than that on the actual gas production of MSFHW, and the influence of high‐pressure condition must be considered when calculating the surface diffusion coefficient. The presented numerical model has important implications for accurate numerical simulation and efficient development of shale gas reservoirs.