A Multiscale Investigation of Cross-Linked Polymer Gel Injection in Sandstone Gas Reservoirs: Implications for Water Shutoff Treatment

Abstract

Excessive water production is a significant challenge during hydrocarbon production from oil and gas reservoirs, and it is typically controlled by polymer gel placement. However, the fundamental process in terms of how precisely this gel reduces water production in gas reservoirs is rarely reported. The objective of paper is to investigate the impact of cross-linked polyacrylamide (poly­(acrylamide-co-acrylic acid) partial sodium salt) gel as a relative permeability modifier for a sandstone/gas/water system and provides insights into the detailed in situ gel behavior inside the porous medium. Stronger gels increased water retention inside the porous media yet decreased the lubrication effect of the gel. Moreover, as the water flow rate increased (during imbibition), the water relative permeability reduction decreased, which is attributed to (a) gel shear thinning behavior and (b) reduction in the residual gas saturation. However, the gel showed shear thickening behavior during gas flow. At low gas flow rates, gel performance is mainly controlled by the gel lubrication effect, while at higher gas flow rates, the significance of gel rigidity is greatly increased. These effects were associated by gas diffusion and gas dissolution in the gel, which in turn expanded the gel layer and reduced gas permeability. Moreover, we identified two counteracting mechanisms (i.e., water retention and lubrication effects) responsible for the disproportionate permeability reduction. In addition, we identified a critical flow rate above which the gel treatment becomes unsuccessful as both effects (i.e., water retention and lubrication) were significantly reduced. These findings thus provide novel insights into the factors leading to successful gel placement to better control water production.

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

“…The micromodel chip was made from borosilicate glass, which has a surface chemistry similar to sandstone (or quartz). 14,44,45 The random rock structure (shown in Figure 2) on the glass plate was made via the isotropic etching method and sealed by another flat glass plate. The full information of the making of such glass micromodels can be found elsewhere.…”

“…The cost-effective Polyacrylamide polymer was used as an RPM agent because it has been widely and successfully applied in oil/gas industry. 13,14,[38][39][40][41][42][43] The polymer solution was prepared by dissolving 1000 ppm of cationic PAM copolymer, Poly (acrylamide-co-diallyldimethylammonium chloride), in 2 wt% KCl brine (Table 1), and this polymer was used as an RPM agent. The dependency of shear stress to shear rate was determined for this polymer solution using a HAAKE RheoWin rheometer.…”

“…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).…”

“…Furthermore, and importantly, the application of 2D micromodels have seen a remarkable growth in the fields of science and engineering, and to investigate the fluid flow in porous media at a microscopic scale. 13,14,22,[33][34][35][36][37] The micromodel literally works as "lab on a chip," and thus allows a systematic investigation of microscale mechanisms responsible for displacement and/or retention in porous media.…”