Experimental evaluation of low concentration scleroglucan biopolymer solution for enhanced oil recovery in carbonate

Abstract

Injection of polymers is beneficial for Enhanced Oil Recovery (EOR) because it improves the mobility ratio between the displaced oil and the displacing injected water. Because of that benefit, polymer flooding improves sweep and displacing efficiencies when compared to waterflooding. Due to these advantages, polymer flooding has many successful applications in sandstone reservoirs. However, polymer flooding through carbonatic rock formations is challenging because of heterogeneity, high anionic polymer retention, low matrix permeability, and hardness of the formation water. The scleroglucan is a nonionic biopolymer with the potential to overcome some of those challenges, albeit its elevated price. Thus, the objective of this work is to characterize low concentration scleroglucan solutions focusing on EOR for offshore carbonate reservoirs. The laboratory evaluation consisted of rheology, filtration, and core flooding studies, using high salinity multi-ionic brines and light mineral oil. The tests were run at 60 °C, and Indiana limestone was used as a surrogate reservoir rock. A rheological evaluation was done in a rotational rheometer aiming to select a target polymer concentration for the injection fluid. Different filtration procedures were performed using membrane filters to prepare the polymer solution for the displacement process. Core flooding studies were done to characterize the polymer solution and evaluate its oil recovery relative to waterflooding. The polymer was characterized for its retention, inaccessible pore volume, resistance factor, in-situ viscosity, and permeability reduction. Rheology studies for various polymer concentrations indicated a target scleroglucan concentration of 500 ppm for the injection solution. Among the tested filtration methods, the best results were achieved when a multi-stage filtration was performed after an aging period of 24 h at 90 °C temperature. The single-phase core flooding experiment resulted in low polymer retention (20.8 μg/g), inaccessible pore volume (4.4%), and permeability reduction (between 1.7 and 2.4). The polymer solution in-situ viscosity was slightly lower and less shear-thinning than the bulk one. The tested polymer solution was able to enhance the oil recovery relative to waterflooding, even with a small reduction of the mobility ratio (38% relative reduction). The observed advantages consisted of water phase breakthrough delay (172% relative delay), oil recovery anticipation (159% and 10% relative increase at displacing fluid breakthrough and 95% water cut, respectively), ultimate oil recovery increase (6.3%), and water-oil ratio reduction (38% relative decrease at 95% water cut). Our results indicate that the usage of low concentration scleroglucan solutions is promising for EOR in offshore carbonate reservoirs. That was supported mainly by the low polymer retention, injected solution viscosity maintenance under harsh conditions, and oil recovery anticipation.

Polymer viscosifier systems with potential application for enhanced oil recovery: a review

“…Hence, the mobility ratio decreases (M 1) and causes a uniform front flow, acting as a piston to push the oil into the producing well, thus increasing the sweep efficiency and the oil recovery factor (Fig. 1b) (Abidin et al, 2012;Ferreira and Moreno, 2020;Kamal et al, 2015a;Thomas, 2016). On the other hand, water flooding increases the mobility ratio (M > 1) due to the lower viscosity of the injected fluid, forming "fingers" in the reservoir, failing to displace a large amount of recoverable oil and reducing the sweep efficiency (El-Hoshoudy et al, 2019;Kamal et al, 2015a;Rellegadla et al, 2017;Fig.…”

“…R RF refers to the ratio between brine permeability before the polymer injection process and after the polymeric solution has flowed through the rock plug (Eq. ( 4)) (Ferreira and Moreno, 2020;Leiting et al, 2010;Maia et al, 2009;Wang et al, 2018a):…”

“…The polymer flooding technique can be applied in several sandstone and carbonate fields in order to increase oil recovery (Ferreira and Moreno, 2020). According to , injection of polymers is not recommended for reservoirs containing oil with viscosity higher than 200 mPa s, because under these conditions it would be necessary to add a very high concentration of polymer, which is not economically feasible.…”

Ion-Specific Effects on the Structure, Size, and Charge of Polymers Applied in Enhanced Oil Recovery

“…Regarding polymer flooding, natural 10 and synthetic 11 macromolecules are both potential candidates in EOR, alone or together with additives. 12,13 For instance, during surfactant− polymer flooding, the amphiphilic molecules gradually decrease the surface tension, and the improved displacing effect and mobility ratio induced by the polymer lead to an increased sweep efficiency.…”

“…Regarding polymer flooding, natural and synthetic macromolecules are both potential candidates in EOR, alone or together with additives. , For instance, during surfactant–polymer flooding, the amphiphilic molecules gradually decrease the surface tension, and the improved displacing effect and mobility ratio induced by the polymer lead to an increased sweep efficiency. , The main requirements for EOR polymers include an optimal molecular weight range, filterability and stability, parameters that are responsible for the solution structure, and subsequent rheological features, as well as durability under the experimental conditions present in the reservoir. As frequently used EOR polymers, partially hydrolyzed polyacrylamides showed good efficiency in tertiary recovery processes, while such an efficiency remarkably decreased at extreme environmental conditions, e.g., at high salinity or elevated temperature .…”