Study On The Multi-scale Mass Transfer Mechanism Of Shale Gas Through Matrix

Shale reservoir matrix storage-permeable space structure features and gas mass transfer mechanism are not well studied yet, which becomes the constraint of shale gas exploration and exploitation. Therefore, in order to provide the basis for the efficient development of shale gas, shale matrix gas multi-scale transfer mechanism was researched.Crop shale from Longmaxi formation was selected, and analyze the mineral composition, porosity and permeability of shale core matrix physical properties. The result shows that the shale matrix quartz brittle mineral content up to 58%, clay mineral is about 27%, and the porosity is 2.89~7.07% and permeability to 0.008 ~0.0514×10-3?m2. Reveals the area of shale reservoir layer low porosity and extra low permeability development, containing a large number of micro nano pore and micro cracks, micro cracks increase the shale matrix porosity, but their degree of connectivity lead to between the permeability and the porosity are bad relevant, and correlation coefficient is 0.19Using field emission scanning electron microscope, mercury injection, low temperature nitrogen adsorption method to characterize the pore structure of shale matrix. Reveals the multi-scale shale matrix pore nanometer to micrometer level development characteristics, based on nano pore, matrix pore which mainly exists in organic matter nano hole and quartz feldspar dissolution mould hole form, the micro fractures are mainly to flake mineral layers form existence; aperture in the pore volume of 2~20nm accounted for than the highest, up to 60% and aperture in 20~50nm pore volume of accounted for than the second, up to about 30%; pore structure approximate variable diameter cylindrical capillary physics model.Evaluation of shale gas mass transfer efficiency by using self assembled matrix pore throat micro fracture "series and parallel" coupling gas mass transfer device. Results show that shale matrix apparent permeability by gas slippage effect and molecular diffusion effect is obvious, the performance of the "parallel" mass flow ratio with the drive for the increase of the pressure difference increases, "series" mass transfer system F-F-M configuration of gas mass transfer capability of the optimal.Based on gas mass transfer experiment with multi-scale features, analysis of the mechanism of gas slippage effect and diffusion effect on the gas transfer process, considering the shale gas reservoir matrix pore throat multi-scale characteristic, gas occurrence, water gas reservoir characteristics, gas mass transfer characteristics of the relationship between each other, consider with gas molecular adsorption layer thickness and the thickness of water film parameters correction of shale gas reservoir effective aperture scale, and the use of variable diameter capillary pore model, improvement of the existing shale gas transfer matrix model, the eventual establishment of a shale matrix by gas adsorption layer thickness and molecular water film thickness, gas diffusion effect, slippage effect of gas in the mass transfer mathematical model, reveal the shale reservoir matrix of natural gas mass transfer mechanism.