Abstract
The original water distribution characteristic plays an important role in the fracturing liquid retention in actual tight reservoirs. In this paper, an analytical model was proposed to characterize the water distribution and its effect on the spontaneous imbibition, based on the capillary tube model and fractal theory. Furthermore, the effect of the water film and the non-piston-like front related to the pore size are included in our model. The proposed model was successfully validated with the experimental results of core imbibition tests. Our work demonstrates that water distribution is influenced by displacement pressure and pore structure. For a small differential pressure, the porous media with richer large pores usually possesses a lower water saturation, and this difference will decrease with the increase of differential pressure. Moreover, compared with previous studies, the proposed imbibition model can not only distinguish the valid pores and invalid pores for imbibition but it can also predict the initial imbibition rate and equilibrium time of tight porous media with different water saturation. The results show that the equilibrium time is controlled by the minimum effective pore radius while the initial imbibition rate is mainly controlled by the large pores. Both of these two parameters will decrease with an increase of water saturation; the former is more sensitive to a low water saturation, while the latter decreases more quickly for a middle-high water saturation.
Highlights
Hydraulic fracturing is the key technology for achieving the production of tight gas reservoirs in a useful and economical way [1,2]
The difference between weight of the saturated samples (Wsat) and Wdry was used to estimate the pore volume (PV), and the results showed that the PV of Sample S1 and S2 were 1.065 cm3 and 1.070 cm3
The spontaneous imbibition of tight porous media with different water saturation is analyzed based on the capillary tube model and fractal theory
Summary
Hydraulic fracturing is the key technology for achieving the production of tight gas reservoirs in a useful and economical way [1,2]. Recognizing the limited pore connectivity of tight porous media, Shi et al (2018) extended the previous fractal model with further consideration of the non-piston-like imbibition in the elongated pore, with the assumption that the spontaneous imbibition can be considered as a laminar flow in different size pores by following the Lucas–Washburn (L–W) equation [20]. An analytical model has been proposed to characterize the water distribution and its effect on the spontaneous imbibition based on the capillary tube model and fractal theory In this model, the effect of water distribution and a non-piston-like front induced by the different pore sizes are included. The variation of interfacial tension and the variation of wettability are ignored
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