Effects of fracturing fluid migration with clay damage after different shut-in period on shale gas production performance

Shale gas wells may experience intentional shut in after fracturing operation partly because of the belief that soaking is beneficial. Although a number of numerical models have been built to analyze the fracturing fluid leak-off problems, neither of those investigate how the effect of fracturing fluid migration (with different shut in time) on the well productivity considering the clay damage in the fracture-face invaded zone. In this work, a numerical model was constructed to demonstrate how far the fluid migration from the fracture face to the matrix in the reservoir under different shut in time. Then, a series of numerical models were used to study the migration of damage zone (by clay dispersion or swelling) on well productivity. Finally, we investigate the damage degrees on well productivity. The results show that the invasion depth is extremely slow (approximately 1.5 m after 100 days of shut-in) due to the compressibility effect of the ultra-low permeability. Whether or not considering the migration caused by kaolinite dispersion or smectite swelling has a minor effect on the gas production, which supports the fact that the longer the shut in period and the better gas production is in the field practice. Furthermore, compared with the kaolinite dispersion damage, the smectite swelling damage not only decrease the absolute permeability, but also increase the capillary pressure in the invasion zone, which harms the gas production and decrease the fracturing fluid recovery efficiency. However, prolonging the shut in time makes the mitigation of water-blocking effect the dominate factor, which is beneficial to the gas production (although the amplification is minimal). Finally, the more serious the damage is, the lower gas production and recovery efficiency are. (C) 2022 The Author(s). Published by Elsevier Ltd.

Automated summary

This study constructed a numerical model to investigate the impact of fracturing fluid migration on shale gas well productivity under different shut-in times. The results showed that the invasion depth of the fluid was extremely slow, and considering the migration caused by clay dispersion or swelling had a minor effect on gas production. Additionally, smectite swelling damage decreased absolute permeability and increased capillary pressure, negatively affecting gas production and fracturing fluid recovery efficiency. Prolonging the shut-in time mitigated the water-blocking effect and benefited gas production.