Mechanisms of how surfactants mitigate formation damage due to aqueous phase trapping in tight gas sandstone formations

Review of the Development Status and Technology of Tight Oil: Advances and Outlook

“…According to the Cambridge Energy Information Agency, the annual production of tight oil in the United States will reach 160 million tons in 2025 and 300 million tons in 2030, accounting for one-third of the total domestic oil production (Figure ). − …”

“…In 2011, directional wells in the United States produced more oil than gas for the first time, and the number of horizontal wells exceeded that of vertical wells. − In 2012, the daily production of tight oil in the United States was 280000 tons. According to the Cambridge Energy Information Agency, the annual production of tight oil in the United States will reach 160 million tons in 2025 and 300 million tons in 2030, accounting for one-third of the total domestic oil production (Figure ).…”

Dynamic Variation of Water Saturation and Its Effect on Aqueous Phase Trapping Damage During Tight Sandstone Gas Well Production

“…Although the water in the capillaries with a radius greater than r bk is mobile water, it could not be completely removed due to the wetting effect of water on the inner surface of the rock pores. Previous studies have shown that the retained water exists in the capillaries ( r > r bk , after the removal of mobile water) in the form of a water film. ,, The volume of the water film cannot be ignored and consequently increases the amount of water saturation in the reservoir. The water contains the immobile water in the capillaries with a radius less than r bk and the water film on the inner surface of the capillaries with a radius greater than r bk .…”

“…APT is governed by irreversible hysteresis effects that do not allow water saturation to revert to a value lower than the irreducible water saturation of a tight reservoir . Previous studies have demonstrated that the irreducible water saturation is dictated by the capillarity in the reservoir; high capillary pressure caused by strong water wettability and narrow pore throats is the main mechanism of water invasion and entrapment. − When the drawdown pressure in a wellbore is far greater than the capillary pressure, the retention of water may not be serious due to enough energy for driving gas and water out; otherwise, the water saturation near the wellbore would be very high. , According to the relationship between water saturation and relative permeability, it is pointed out that serious APT damage is corresponding to high water saturation, and the threshold pressure gradient effect should not be ignored. − Permeability damage ratio (DR), APT index or modified APT index, phase trapping coefficient (PTC), and phase trapping index (PTI) were proposed to predict the potential tendency of a reservoir for establishment of phase traps. ,, Classically, DR is the most basic and most widely used tool since it is an actual APT test in the laboratory . Earlier scholars usually researched the APT damage caused by the working fluid invasion in the processes of drilling and completion, fracturing, workover, and so forth. ,− The severity of APT damage increases as each of the initial water saturation, permeability, and drawdown pressure decreases, and viscosity of water increases. , Nevertheless, few investigations focused on the research of the APT damage caused by increased water saturation near a wellbore during tight sandstone gas well production .…”

“…Figure13. Curves of wetting contact angle vs critical capillary radius and water saturation in case of a 2.5 MPa drawdown pressure without liquid loading.…”