Mechanism Study of Disproportionate Permeability Reduction Using Nuclear Magnetic Resonance T2

Abstract

Excessive water production is an enduring problem in the oil industry that has always been an unbearable burden on the environment and a great damage to the ultimate oil recovery. Gel treatment has been routinely used for decreasing water production. Disproportionate permeability reduction (DPR) is a natural phenomenon in some polymer gels that can reduce the permeability to water more than to oil. The conformance improvement treatments with DPR can effectively reduce the water cut without substantially reducing the oil productivity in fractured reservoirs. At present, there are no widely accepted mechanisms of oil-phase permeability development and DPR. In this paper, nuclear magnetic resonance is applied to study the mechanisms of oil-phase permeability development, DPR, and permeability influence by scanning different core samples treated with Cr­(III)–acetate–hydrolyzed polyacrylamide polymer gels. Results show that the permeability difference leads to a certain alteration in NMR T2 curves, but final conclusions for the mechanisms are consistent. For the mechanism of oil-phase permeability development, initially, gel displacement in large pores accounts for the oil permeability development, after which the gel dehydration becomes the main mechanism. The mechanisms for DPR include the blocking of flow channels by gel rehydration and residual oil and the low permeability of gel relative to water. The results can be used to optimize the utility of polymer gels with a DPR property.

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

“…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).…”

“…The permeability reduction gradually increased as the injected PV of brine increased, however the RPM performance did not reach to stable situation even though the injected brine volume was relatively higher than the previous study, 21 that is, 300 PV and 650 PV of a synthetic brine were injected into a treated synthetic core (1900 mD) and Elgin sandstone (2400 mD), respectively. Moreover, Liang et al and Liang et al 13,22 studied the effect of oil injection volume on oil permeability reduction in chromium acetate cross-linked hydrolysis polyacrylamide gel treated sandstone cores (2.3 D). During the oil injection period, the oil permeability reduction gradually decreased and even after injecting 110 PV of oil, the RPM did not reach ultimate stability.…”

“…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.…”