Low-Salinity-Assisted Cationic Polyacrylamide Water Shutoff in Low-Permeability Sandstone Gas Reservoirs

Abstract

The application of polymer-based relative permeability modifiers (RPM) in low-permeability sandstone reservoirs has long intrigued production engineers. We hypothesize that lowering salinity may expand the application of the cationic polyacrylamide (CPAM) in low-permeability sandstone gas reservoirs, because of the favorable polymer–polymer physiochemical interaction at pore surfaces. To test this hypothesis, we conducted six core-flooding experiments to examine the relative permeabilities of water/gas before and after CPAM treatment, as a function of salinity using sandstone core plugs. Moreover, we measured zeta potentials of polymer–polymer, rock–polymer, and rock–brine interfaces before and after the RPM treatment, as a function of salinity. We also measured the contact angles for silicate/brine systems before and after the treatment as a function of salinity. Core-flooding results show that reducing the salinity decreases the water relative permeability but with marginal effect on the gas relative permeability. Lowering salinity also decreases the effective polymer layer thickness at pore surfaces. Moreover, the adsorption of the CPAM onto the negatively charged sandstone rock, together with lowering brine salinity, increases hydrophobicity of the rock. Thus, our results suggest that polymer–polymer interactions at pore surfaces govern the performance of CPAM in low-permeability sandstone rocks.

Impact of prolonged water‐gas flow on the performance of polyacrylamide

“…This observation is consistent with previous studies. 1,27,44,49,50 It has been explained that such formation of dynamic polymer layer occurs because of two successive events. Initially, a few hundred nanometers of adsorbed polymer layer forms where some of adsorbed polymer acrylamide groups that do not carry a positive charge stick out towards the pore center.…”

“…Natural gas is entering a significant development phase based on the global energy requirements that have identified natural gas as a transition fuel (Paris Agreement, 2015) to promote sustainable and clean energies. [1][2][3][4][5][6][7][8][9] However, for mature gas reservoirs, excessive water production is a major challenge that has the potential to hinder this growth. To counter this, polymer treatments are frequently utilized in oil and gas wells to reduce water production (i.e., water shut-off treatment using relative permeability modifiers, RPM).…”

“…To counter this, polymer treatments are frequently utilized in oil and gas wells to reduce water production (i.e., water shut-off treatment using relative permeability modifiers, RPM). 1,[10][11][12][13][14][15][16][17] However, there is still a lack of understanding of how polymers make a variation in permeability, a feature associated with polymer injection known as "disproportionate permeability reduction (DPR)." Mechanistically, wall effects are caused by adsorption of polymer molecules on the pore surfaces, which then reduce the pore throat radii (i.e., steric effect) leading to a significant permeability reduction.…”

“…[18][19][20] The thickness of the adsorbed polymer layer and subsequently RPM performance change with time due to other underlying effects, such as the volume of injected fluid, the flowing fluid composition, brine salinity, and the rheological properties of the polymer. 1,[10][11][12][13][14][21][22][23][24][25] Even though the use of polymers as RPM have already been proven, the efficiency period of RPM is still questionable. The performance of RPM may reduce over time due to RPM removal during production of reservoir fluid (water and oil).…”

Extensional Rheological Measurements of Surfactant–Polymer Mixtures

“…Cationic polyacrylamide (CPAM) with better thermal stability has also been investigated for mobility control applications in recent times. Research conducted by Al-Shajalee et al 55 revealed that cationic polymer at low salinity conditions could be a potential option to selectively reduce the water relative permeability without affecting gas relative permeability during the water-shut off treatment in gas sandstone reservoirs.…”