Characterization of pore structure, gas adsorption, and spontaneous imbibition in shale gas reservoirs

- LF-NMR, X-ray nano-CT, FE-SEM experiments are conducted to characterize the properties of shale gas reservoirs.
- The contents of adsorption gas and free gas increase with increasing gas pressure, of which the free gas increases faster.
- NMR results indicate that the capillary effect dominates the early stage of the fluid transport, and disappear gradually.

The multiscale pore structure and its distribution as well as the occurrence state of shale gas and spontaneous imbibition in gas shale are studied experimentally. Most of the pores within organic matters are at nanoscale and are isolated in all directions. They have low porosity and connectivity, which account for the most of pore volume and determine the resource abundance of gas shale reservoirs. The contents of adsorption gas and free gas in the multiscale pore structure of shale rocks increase with the increase of gas pressure, of which the free gas increases faster than that of adsorption gas. The spontaneous imbibition shows the fast shift of T2 peaks to right at early stage of fluid transport through the interconnected network of pore structure in shale rocks. Our results may provide unified methods for clear understanding of the pore structure and fluid transport behavior in shale gas reservoirs and assist the future efficient exploitation of shale gas.