Abstract

Less than half of the injected fracturing fluid in gas shale is often recovered and in many cases the flowback efficiency is <20%, which relates to potential productivity hindrance. Some have suggested that the water migration in the neighborhood of fractures induced by spontaneous imbibition contributes to auto-removal mechanism of water damage. However, water imbibition into fractured shale reservoirs is a physic-chemical and multiscale flow process, which is significantly different from conventional reservoirs. Therefore, we systematically characterize the samples by measuring the porosity, permeability, wetting angle and mineral composition. Comparative imbibition experiments are performed on 18 binary core plugs from typical formations of China's basin (i.e., Ordos Basin, Songliao Basin and Sichuan Basin). The preliminary result shows that Handy imbibition model has an evident deviation in predicting the shale imbibition experiment result, which is significantly overestimated. This disagreement can be explained by strong fluid-wall interactions in micron-nano pores. In addition to the widely believed capillary driving forces and viscous forces, the overall resistance of fluid-wall interactions have an important impact on water migration, which could reduce the imbibition rate in gas shale. A critical aperture Dc of about 36~100nm exits, which can be used to address the effects of fluid-wall interactions. The matrix blocks with average pore size of > Dc tend to produce minor resistance effects of fluid-wall interaction on imbibition rate. Handy model can provide a good match with experimental imbibition in micro-fractures or macropores; in the contrary, the matrix blocks with average pore size of <Dc tend to exert significant resistance effects of fluid-wall interaction on imbibition rate. Handy model reproduce the global trend of variation, which has been inadequate. The results of our study are more valuable for the comprehension of auto-removal water damage process and optimization of flowback time after fracturing operations in gas shale.

You do not currently have access to this content.