A Systematic Study of Alkaline-Surfactant-Gas Injection as an EOR Technique

Abstract

Alkaline-Surfactant-Polymer (ASP) flooding is an attractive enhanced oil recovery method. However, some reservoir conditions are not favorable for the use of polymers or their use would not be economically attractive due to low permeability or other unfavorable conditions. Foam can be an alternative to polymer for improving the displacement efficiency in chemical-EOR process. The use of foam as a mobility control agent by co-injection or alternate injection of gas and chemical slug is termed, here, as Alkaline-Surfactant-Gas (ASG) Process. Foam reduces the relative permeability of the injected chemical slug that forms microemulsion at ultra-low oil-water interfacial tension (IFT) and generates sufficient viscous pressure gradient to drive the foamed chemical slug. The concept of ASG process as an enhanced oil recovery technique is relatively new, with very little experimental and theoretical work available on the subject. Polymer is replaced by foam in corefloods experiments as a mobility control agent. Phase behavior and ASG coreflood experiments were carried out to identify high performance chemicals, designed for both foaming and strong IFT reduction performance. The coreflood experiments were performed on sandstone and dolomite rock samples. Oil recovery and coreflood pressure response were evaluated to determine the success of the process. Different injection strategies for foam generation were investigated, and mechanisms of mobility control by foam were studied. Several promising surfactants, with dual properties of foaming and emulsification, were identified and used in the coreflood experiments. Maximum recovery of 95% of remaining oil after waterflood was observed. Oil recovery and pressure responses from ASG experiments are comparable to ASP coreflood experiments carried out under similar conditions. Experimental data show a strong synergic effect of foam and ultra-low oil-water IFT on oil recovery. Compared to polymer, foam has lower cost associated with its use and is less susceptible to biological, shear, and thermal degradation. The use of foam in chemical EOR can reduce the technical disadvantages associated with polymer in low permeability and fractured reservoirs. Introduction Polymer is widely used for mobility control in enhanced oil recovery (EOR) processes. In Alkaline-Surfactant-Polymer (ASP) process, polymer provides mobility control during ASP slug and polymer drive injection. However, there are several disadvantages of using polymer. Some of the major disadvantages are: - High molecular weight polymers can plug rocks with very low permeability, or if a lower molecular weight polymer is used to avoid plugging, then the cost of using polymer increases and eventually becomes uneconomic. - Many of the commercially available EOR polymers can be unstable at high temperature. - Some polymers can mechanically degrade due to high shear stress through chokes or perforations at high flow rate. - There can be other problems with polymers under some conditions associated with unfavorable interactions with surfactants.

Review of surfactant-assisted chemical enhanced oil recovery for carbonate reservoirs: challenges and future perspectives

“…However, even then, complications, for example, viscous instabilities and gravity segregation, especially for heterogeneous reservoirs could not be defeated (Rogers and Grigg 2001). As a possible solution to these complications, foam-assisted EOR, such as the alkali-surfactant-gas (ASG) process, is one of the newly introduced successful synergistic combination of chemical and gas EOR methods, especially for carbonate reservoirs (Li et al 2010;Srivastava et al 2009). The ASG process exhibits lower mobility in high-permeability layers and hence understandably blocks or hinders the flow in these layers.…”

Enhanced oil recovery by alkaline-surfactant-alternated-gas/CO2 flooding

“…The test tubes were then shaken in Tarsons Rotospin Rotary Mixer at a speed of 50 rpm for 6 h, which resulted in the formation of foam at the top of the liquid column. After foam generation, the initial foam volume (V i ) and the time for dewatering half volume from foam (t 1/2 ) were noted by visual observation (Srivastava et al 2009;Bera et al 2013). To measure the foaming ability of a particular system, the foaming ability coefficient (F q ) was used, which was defined as (Wang et al 2001):…”

“…The core flood system consisted of three liquid pumps, a CO 2 cylinder with regulator and gas flow controller, back-pressure regulator (BPR), Hassler core holder, pressure transducers, data acquisition system, and oven. The ASG flooding experiments were conducted with the same procedures as followed by previous authors (Syahputra et al 2000;Liu 2007;Srivastava et al 2009;Yin et al 2009;Samanta et al 2012). After the core plug was prepared by cleaning and drying, its weight was taken and the pore volume (PV) of the core plug was determined from its dimensions and porosity.…”

“…The presence of synthetic surfactants and natural soaps assists in further lowering of IFT to ultra-low value (< 0.01 mN/m) resulting in the formation of more stable foam which in turn increases the oil recovery efficiency. The process of co-injection or alternate injection of gas and alkali-surfactant slug which results in the formation of foam in the porous media is termed in the literature as alkali surfactant gas (ASG) or alkaline-surfactant-alternated-gas (ASAG) or low-tension gas process (Srivastava et al 2009(Srivastava et al , 2011Cottin et al 2012;Guo et al 2012;Lashgari et al 2015).…”

Systematic Phase Behaviour Study and Foam Stability Analysis for Optimal Alkaline/Surfactant/Foam Enhanced Oil Recovery

“…In cases where foam is injected into swept zones with low oil saturation, intermediate or low stability foam in presence of oil may be adequate (Mannhardt et al, 2000). Foam has been identified also as an attractive alternative to polymer in the ASP flooding for either low permeability reservoirs with high salinity formation water (Lawson & Reisberg, 1980;Srivastava et al, 2009). Foam offers better properties over polymers for conformance issues.…”