Investigation of gas flow hindrance due to fracturing fluid leakoff in low permeability sandstones

• We conducted an experimental study to better understand the effects of leak off.
• Leakoff volume has a greater impact on regained permeability than shut-in time.
• Saturation within the invaded zone is a key determinant of gas flow.
• Lower permeability formations are more sensitive to leak off.
• Increased shut-in time is not always synonymous with improved regained permeability.

Hydraulic fracturing has become a necessary practice in order to attain economical gas flow rates from low permeability formations. During and immediately following the creation of a fracture, high injection pressures cause fracturing fluid to leak off into the adjacent matrix. This work focuses on the impact of fracturing fluid leak off on gas flow through tight formations as a function of leakoff volume and shut-in time.It was observed that an increase in leakoff volume reduces effective permeability to gas while an increase in shut-in time increases it. Gas flow hindrance caused by the leak off of water-based fracturing fluid is mitigated by shut-in time in that it favors spontaneous redistribution of the fluid deeper into the rock matrix. However, results from this work demonstrate that the flow hindrance caused by the initial leak off is superior to the effective permeability gains by shut-in time. This imbalance highlights a key determining factor behind gas flow hindrance due to fracturing fluid leak off – fluid saturation in the neighborhood of the fracture.The properties of the formation were found to also play a significant role in determining regained permeability. Lower formation permeability slows improvements to gas flow due to lower mobility of the invading fluid despite expected higher capillarity. Furthermore, the extension of these observations to rock formations with lower permeability, such as tight sand and shale, suggests that shut-in time may have an insignificant impact on regained permeability improvement in systems with depressed relative permeability curves.Leakoff volume and shut-in time are variables that work differently to dictate saturation distribution in the neighborhood of the fracture. Saturation within the invaded zone and characteristics of the formation's relative permeability curve may be the key determinants of gas flow hindrance following hydraulic fracturing activities. This may explain the lack of trends in the field – conditions vary between formations.