Formulation for chemical EOR: Development and evaluation of an ASP formulation In customer field conditions

Alkali surfactant polymer (ASP) flooding is an enhanced oil recovery (EOR) technology with an impressive potential for increasing incremental oil production from conventional hydrocarbon bearing reservoirs. A challenge to ASP application is the complexity of determining an effective formulation, typically requiring extensive laboratory screening of nearly countless combinations of surfactants and cosolvents. This paper focuses on demonstrating the utility of the hydrophilic–lipophilic deviation (HLD) concept for EOR application to simplify surfactant formulation workstreams seeking an economically viable ASP formulation for field application. In describing work performed for EOR application of ASP under customer conditions using crude oil, the discussion covers the initial evaluation of the promising surfactant formulation (interfacial tension and solubility), the improvement upon the formulation via HLD principles, and the evaluation of the improved surfactant formulation (coreflood studies). The final ASP formulation identified consisted of a 9 to 1 mixture of alkyl propoxy sulfate sodium salt (APS) to alkyl ethoxy sulfate sodium salt (AES) totaling 2000 ppm active surfactant content, 2.0 wt% Na₂CO₃, and 3000 ppm polyacrylamide polymer (all commercially available products). This formulation had ultra-low interfacial tension and favorable mixing behavior under reservoir conditions. In coreflood studies, the final formulation reproducibly achieved cumulative oil recovery of 96.4%–98.5% of original oil in place with only 0.3 PV of ASP injection with a chase alkali polymer injection.     

Salt-Induced Constructions of Gemini-like Surfactants at the Interface and Their Effects on the Interfacial Tension of a Water/Model Oil System

It is an urgent issue to enhance oil recovery for unconventional reservoirs with high salinity. Focused on this topic, salt addition is a powerful tool to motivate the surfactant assembly at the water/oil interface and improve the interfacial activity. We used a cationic surfactant cetyltrimethylammonium bromide (CTAB) and an anionic salt dicarboxylic acid sodium (CnDNa) to construct gemini-like surfactants at the interface and evaluated their ability to reduce the interfacial tension (IFT) between model oil (toluene and n-decane, v:v = 1:1) and water. Interestingly, the fabrication of a (CTAB)₂/C4DNa gemini-like surfactant was hardly achieved at the fresh water/model oil interface, but accomplished at the brine/model oil interface. At a high NaCl concentration (100,000 mg L⁻¹), the IFT value is reduced to 10⁻³ mN m⁻¹ order of magnitude, which is generally desired in practical applications. The control experiments displacing the surfactant type and the spacer length further confirmed the NaCl effects on the interfacial assembly.     

Synergistic surfactant mixtures containing lignosulphonates

Enhanced oil recovery (EOR) schemes have been gaining importance over the past several years. Of the various methods being tested, surfactant (or micellar) flooding appears to be one of the most promising ones. It involves injecting into the well the solution of a surfactant which reduces the inter-facial tension between the displacing aqueous solution and the oil trapped in the reservoir. Depending on the concentration of the surfactant, oil displacement proceeds either by a miscible process (surfactant concentration > 10%) or by a immiscible process (surfactant concentration = 2–3%). Miscible flooding converts to the immiscible process as the system is diluted by connate (interstitial) water. Under immiscible conditions, the most significant parameter affecting recovery is the interfacial tension^(1,2). Petroleum sulfonates are perhaps the most important group of surfactants capable of producing very low interfacial tensions between crude oil and the water phase. Their relatively high cost, however, renders many potential applications uneconomical.     

Characterizations of surfactant synthesized from Jatropha oil and its application in enhanced oil recovery

Surfactants are frequently used in chemical enhanced oil recovery (EOR) as it reduces the interfacial tension (IFT) to an ultra‐low value and also alter the wettability of oil‐wet rock, which are important mechanisms for EOR. However, most of the commercial surfactants used in chemical EOR are very expensive. In view of that an attempt has been made to synthesis an anionic surfactant from non‐edible Jatropha oil for its application in EOR. Synthesized surfactant was characterized by FTIR, NMR, dynamic light scattering, thermogravimeter analyser, FESEM, and EDX analysis. Thermal degradability study of the surfactant shows no significant loss till the conventional reservoir temperature. The ability of the surfactant for its use in chemical EOR has been tested by measuring its physicochemical properties, viz., reduction of surface tension, IFT and wettability alteration. The surfactant solution shows a surface tension value of 31.6 mN/m at its critical micelle concentration (CMC). An ultra‐low IFT of 0.0917 mN/m is obtained at CMC of surfactant solution, which is further reduced to 0.00108 mN/m at optimum salinity. The synthesized surfactant alters the oil‐wet quartz surface to water‐wet which favors enhanced recovery of oil. Flooding experiments were conducted with surfactant slugs with different concentrations. Encouraging results with additional recovery more than 25% of original oil in place above the conventional water flooding have been observed. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2731–2741, 2017     

Surfactant Enhanced Oil Recovery in a High Temperature and High Salinity Carbonate Reservoir

The goal of this work was to find an effective surfactant system for enhanced oil recovery after water injection substituting for oil at a vuggy fractured reservoir with a high temperature and high salinity (220,000 mg/L). Four types of surfactants with concentrations (less than 0.2 %) were screened. Washing oil experiments were conducted in Amott cells. A surfactant system was established by mixing a surfactant with best ultimate recovery and one with best recovery rate. The optimized surfactant system could recover 50 % of remaining oil. To study the mechanism of enhanced oil recovery after water injection substituting oil, interfacial tension (IFT) and contact angle were measured. Experimental results showed that surfactants with good washing ability had low IFT, but surfactants with low IFT may not have a good washing ability. IFT had no obvious relationship with the increased oil recovery or washing ability. The optimized system could not alter carbonate to decrease the oil‐wetting capability. Though octadecyl trimethyl ammonium chloride had a good ability wet the carbonate with water, it could not recover much oil. Therefore, except for interfacial tension and wettability alteration, there must be other parameters dominating oil recovery after water injection substituting for oil.     

Synthesis and solution properties of poly(acrylamide-styrene) block copolymers with high hydrophobic content

Hydrophobically associating block copolymers of polyacrylamide/styrene with a high hydrophobe content were synthesized using micellar copolymerization under various conditions of surfactant and initiator concentrations with the objective of determining the conditions that produce optimum solution properties for enhanced oil recovery. Solubilities, aqueous solution viscosities and interfacial properties with air and oil of the copolymers were investigated. The influence of salt on the solution properties was also studied. Nature of hydrophobic sites and onset of hydrophobic association were studied by measuring the fluorescence of pyrene in polymer solutions. Optimum solution properties were obtained for copolymers synthesized under conditions of high surfactant and initiator concentrations. The copolymers displayed substantial thickening properties at low concentrations with enhanced thickening in the presence of salt. The interfacial tensions of the aqueous solutions with n-decane and air were also reduced. Interfacial properties were slightly sensitive to salt concentration. The copolymer solutions showed shear and temperature thinning behaviors typical of polymer solutions.     

Novel fluorinated surfactants for enhanced oil recovery in carbonate reservoirs

Novel surfactant‐polymer (SP) formulations containing fluorinated amphoteric surfactant (surfactant‐A) and fluorinated anionic surfactant (surfactant‐B) with partially hydrolyzed polyacrylamide (HPAM) were evaluated for enhanced oil recovery applications in carbonate reservoirs. Thermal stability, rheological properties, interfacial tension, and adsorption on the mineral surface were measured. The effects of the surfactant type, surfactant concentration, temperature, and salinity on the rheological properties of the SP systems were examined. Both surfactants were found to be thermally stable at a high temperature (90 °C). Surfactant‐B decreased the viscosity and the storage modulus of the HPAM. Surfactant‐A had no influence on the rheological properties of the HPAM. Surfactant‐A showed complete solubility and thermal stability in seawater at 90 °C. Only surfactant‐A was used in adsorption, interfacial tension, and core flooding experiments, since surfactant‐B was not completely soluble in seawater and therefore was limited to deionized water. A decrease in oil/water interfacial tension (IFT) of almost one order of magnitude was observed when adding surfactant‐A. However, betaine‐based co‐surfactant reduced the IFT to 10^?3 mN/m. An adsorption isotherm showed that the maximum adsorption of surfactant‐A was 1 mg per g of rock. Core flooding experiments showed 42 % additional oil recovery using 2.5 g/L (2500 ppm) HPAM and 0.001 g/g (0.1 mass%) amphoteric surfactant at 90 °C.     

A Zwitterionic Surfactant Bearing Unsaturated Tail for Enhanced Oil Recovery in High‐Temperature High‐Salinity Reservoirs

High‐temperature/high‐salinity (HTHS) reservoirs contain a significant fraction of the world's remaining oil in place and are potential candidates for enhanced oil recovery (EOR). Selection of suitable surfactants for such reservoirs is a challenging task. In this work, two synthesized zwitterionic surfactants bearing a saturated and an unsaturated tail, namely 3‐(N‐stearamidopropyl‐N,N‐dimethyl ammonium) propanesulfonate and 3‐(N‐oleamidopropyl‐N,N‐dimethyl ammonium) propanesulfonate, respectively, were evaluated. The surfactant with the unsaturated tail showed excellent solubility in synthetic seawater (57,643 ppm) and in formation brine (213,734 ppm). However, the unsaturated surfactant with a saturated tail showed poor solubility, and therefore it was not evaluated further. The thermal stability of the synthesized unsaturated surfactant solution in seawater was evaluated by heating the solution at 90 °C in a sealed aging tube for 2 weeks. The thermal stability of the unsaturated surfactant was confirmed by FTIR and NMR analysis of the aged samples at such harsh conditions. The critical micelle concentration (CMC) of the synthesized unsaturated surfactant in seawater was 1.02 × 10^?4 mol L^?1, while the surface tension at CMC was 30 mN m^?1. The synthesized unsaturated surfactant was able to reduce the oil–water interfacial tension to ~10^?1 mN m^?1 at different conditions. A commercial copolymer of acrylamide and 2‐acrylamido‐2‐methylpropane sulfonic acid (AM‐AMPS) was tested for EOR applications in HTHS conditions. The addition of the synthesized unsaturated surfactant to the AM‐AMPS copolymer increased the viscosity of the system. The increase in oil recovery by injecting the unsaturated surfactant solution and the surfactant–polymer mixture in solution was 8 and 21%, respectively. The excellent properties of the synthesized unsaturated surfactant show that surfactants with an unsaturated tail can be an excellent choice for HTHS reservoirs.     

Syntheses and surface active properties of cationic surfactants having multi ammonium and hydroxyl groups

In this study, cationic surfactants having mono-, di-, and tri-amminium groups were synthesized by the condensation reaction of alkyl glycidyl ether and alkyl amine followed by the quarternization with dimethyl sulfate. The structure of the product was elucidated by ¹H NMR and FT-IR. The minimum surface tension achieved using C12-BHDM surfactant was around 28.88 mN/m, which suggests that C12-BHDM can be used to reduce the surface tension of primarily aqueous formulations and to act as emulsifiers. Dynamic surface tension measurement using a maximum bubble pressure tensiometer indicated that much longer time was required to reach an equilibrium value presumably due to the low mobility rate of a surfactant molecule with high molecular weight. The interfacial tensions measured between 1 wt.% surfactant solution and n-decane were found to be in the same order of magnitude as those exhibited between micellar solutions and nonpolar hydrocarbon oils. It has been observed that the results for foam stability measurement are consistent with those of CMC and contact angle. That is, the percentage of foam volume decrease has been observed to increase with an increase in number of ammonium and hydroxyl groups.     

Experimental Study of Nanofluids Applied in EOR Processes

Nanoemulsions are small droplet-sized systems that have low surface tension and a small percentage of active material in their composition. In this study, low oil content nanoemulsion systems were developed for the use in enhanced oil recovery (EOR). The experiments were performed on a device capable of simulating petroleum reservoir conditions using sandstone rock cores. Nanoemulsions were obtained from a pre-selected microemulsion system composed of: RNX95 as surfactant, isopropyl alcohol as cosurfactant, kerosene as oil phase, and distilled water as aqueous phase. Different percentages of polyacrylamide were added to the systems obtained to evaluate the influence of viscosity in EOR results. The nanoemulsion droplet sizes ranged from 9.22 to 14.8 nm. Surface tension values were in the range of 33.6–39.7  dyn/cm. A nanoemulsion system with 2.5 wt% surfactant was used in EOR assays. The oil recovery was directly proportional to polymer percentage in the nanoemulsion, ranging from 39.6 to 76.8%. The total oil in the place recovery ranged from 74.5 to 90%.     

Investigation of silica nanoparticles grafted with sulphonated polymer for enhanced oil recovery at high temperature and high salt

Nano-fluids' application for enhanced oil recovery (EOR) has attracted noticeable attention and formed a new research area in recent years. Currently, the greatest challenge in this area is to formulate stable nano-fluids for oil reservoirs with high temperatures and salinity. To overcome the limitations of its application in high-temperature drilling, polymer-coated nanoparticles (SiO₂-PAMPS NPs) were prepared via solution polymerization of 2-acrylamide-2-methyl-1-propane sulphonic acid (AMPS) from the surface of aminopropyl-functionalized silica nanoparticles. The SiO₂-PAMPS NPs were characterized by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and dynamic light scattering (DLS). The results indicated that the AMPS was successfully grafted onto the surface of silica nanoparticles, and the average diameter of SiO₂-PAMPS NPs was about 16 nm. The nano-fluids showed noticeable stability in American Petroleum Institute (API) brine (2 wt.% CaCl₂ and 8 wt.% NaCl) at 90°C beyond 46 days. When amphipathic nanoparticles were introduced to brine at 90°C, the potential of the nano-fluids in recovering oil was evaluated by investigating the interfacial tension with kerosene oil and the oil contact angle in the nano-fluids. The contact angle of the glass sheet surface before treatment was about 144°, while after SiO₂-PAMPS NPs treatment for 72 h, it became about 92°. Meanwhile, the nano-fluids showed an excellent enhancing emulsibility property, which plays a vital role in promoting the development of EOR in high-temperature and high-salt environments.     

Gemini表面活性剂的特性及耐盐活性研究

研究了疏水链长度不同和联接基长度不同的7种系列阴离子Gemini表面活性剂的表/界面活性。它们的表面张力和临界胶束浓度表明它们有很好的表面活性。它们有非常好的抗一价、二价盐的能力,在20%以上的NaCl盐水中仍能溶解。用高矿化度的中原油田盐水配制的活性剂溶液与原油间的界面张力能达到超低,表明它们可应用于特高矿化度油藏提高采收率。     

The use of inorganic sacrificial agents in combination with surfactants in enhanced oil recovery

Current literature on optimization of surfactants in enhanced oil recovery is summarized. Effectiveness of the use of surfactants in chemical EOR processes is dependent on many factors. Uncontrollable factors such as reservoir parameters, minerology, and the nature of the crude oil influence the choice of a chemical process. Each reservoir offers a different set of problems to be solved. When the use of a surfactant is warranted, one attempts to optimize further the activity of this surfactant by modifying the chemistry of the reservoir system. Cost aside, maintenance of optimal surfactant activity is essential to minimize the oil/water interfacial tension. Also, loss of surfactant activity due to adsorption on substrate material is particularly disadvantageous because the water wet nature of the rock may be decreased. The use of alkaline, weak acid anions, such as sodium silicate, phosphate and carbonate to enhance surfactant effectiveness has been studied. These sacrificial agents can reduce the hardness (divalent cation) activity of the solution and compete with surfactant for active sites on the reservoir rock surface. Core flood results show that there is an inverse correlation between surfactant retention in the core and residual oil recovery. They also suggest that surfactants may be recovered for reinjection by the optimal use of sacrifical agents-in particular, the sodium silicates.     

低渗砂岩岩心AESO3表面活性剂驱油室内效果评价

随着我国低渗透油田步入三次采油阶段,三次采油用表面活性剂的研究成为当前研究的重点。ZC油田长2储层是典型的低渗透储层,本次为其选取了AESO3表面活性剂,其抗盐性与表面张力均符合长2储层流体的要求,本次选用的表面活性剂可以将储层驱油效率平均提高5.7%,将储层水相渗透率平均提高10%。     

A Review of Gemini Surfactants: Potential Application in Enhanced Oil Recovery

Gemini surfactants are a group of novel surfactants with more than one hydrophilic head group and hydrophobic tail group linked by a spacer at or near the head groups. Unique properties of gemini surfactants, such as low critical micelle concentration, good water solubility, unusual micelle structures and aggregation behavior, high efficiency in reducing oil/water interfacial tension, and interesting rheological properties have attracted the attention of academic researchers and field experts. Rheological characterization and determination of the interfacial tension are two of the most important screening techniques for the evaluation and selection of chemicals for enhanced oil recovery (EOR). This review deals with rheology, wettability alteration, adsorption and interfacial properties of gemini surfactants and various factors affecting their performance. The review highlights the current research activities on the application of gemini surfactants in EOR.     

国内外强化采油用表面活性剂研究进展

中国石油对外依存度持续上升,而采收率持续下降。中国剩余石油储量中大部分为高温高盐、低渗透、稠油油藏等难以开采的苛刻油藏。化学驱强化采油技术目前所使用的石油磺酸盐、烷基苯磺酸盐等常规表面活性剂由于活性低、耐盐性差而导致低效甚至无效。综述了新型表面活性剂,如阴-非离子表面活性剂、双子及寡聚表面活性剂、甜菜碱型两性表面活性剂、高分子表面活性剂、烷基糖苷表面活性剂、黏弹性表面活性剂、生物表面活性剂、阴阳离子混合表面活性剂等的研究进展。讨论了国内外强化采油用表面活性剂评价方法的差异。最后,对采油用表面活性剂的发展方向进行了展望。     

油水界面上阴/阳离子型复配表面活性剂体系的分子动力学模拟

采油过程中阴/阳离子型表面活性剂复配使用可显著增强驱油效果,对其微观机理的深入研究有助于驱油用表面活性剂的结构优化设计及使用。采用分子动力学方法研究了不同摩尔比的阴离子表面活性剂聚醚羧酸钠(PECNa)和阳离子表面活性剂十八烷基三甲基氯化铵(OTAC)复配体系在油水界面上的分子行为和物理性质。结果表明,复配体系比单种表面活性剂体系更有利于降低油水界面张力。不同复配比体系中,两种表面活性剂头基相反电荷间的吸引作用使表面活性剂之间对各自反离子的静电吸引作用减弱,且等摩尔比体系尤为明显。阴离子表面活性剂的亲水头基对阳离子表面活性剂亲水头基形成的水化层内水分子的结构取向无显著影响,反之亦然。通过调节两种离子型表面活性剂的复配比例,可调整油水界面吸附层微观结构,有望降低油水界面张力,提高采收率。     

Viscoelastic Surfactants with High Salt Tolerance,Fast‐Dissolving Property,and Ultralow Interfacial Tension for Chemical Flooding in Offshore Oilfields

Injected chemical flooding systems with high salinity tolerance and fast‐dissolving performance are specially required for enhancing oil recovery in offshore oilfields. In this work, a new type of viscoelastic‐surfactant (VES) solution, which meets these criteria, was prepared by simply mixing the zwitterionic surfactant N‐hexadecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propane sulfonate (HDPS) or N‐octyldecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propane sulfonate (ODPS) with anionic surfactants such as sodium dodecyl sulfate (SDS). Various properties of the surfactant system, including viscoelasticity, dissolution properties, reduction of oil/water interfacial tension (IFT), and oil‐displacement efficiency of the mixed surfactant system, have been studied systematically. A rheology study proves that at high salinity, 0.73 wt.% HDPS/SDS‐ and 0.39 wt.% ODPS/SDS‐mixed surfactant systems formed worm‐like micelles with viscosity reaching 42.3 and 23.8 mPa s at a shear rate of 6 s^?1, respectively. Additionally, the HDPS/SDS and ODPS/SDS surfactant mixtures also exhibit a fast‐dissolving property (dissolution time <25 min) in brine. More importantly, those surfactant mixtures can significantly reduce the IFT of oil–water interfaces. As an example, the minimum of dynamic‐IFT (IFT_min) could reach 1.17 × 10^?2 mN m^?1 between the Bohai Oilfield crude oil and 0.39 wt.% ODPS/SDS solution. Another interesting finding is that polyelectrolytes such as sodium of polyepoxysuccinic acid can be used as a regulator for adjusting IFT_min to an ultralow level (<10^?2 mN m^?1). Taking advantage of the mobility control and reducing the oil/water IFT of those surfactant mixtures, the VES flooding demonstrates excellent oil‐displacement efficiency, which is close to that of polymer/surfactant flooding or polymer/surfactant/alkali flooding. Our work provides a new type of VES flooding system with excellent performances for chemical flooding in offshore oilfields.     

Progress in research of sulfobetaine surfactants used in tertiary oil recovery

The synthesis of sulfobetaine surfactants and their application in tertiary oil recovery (TOR) are summarized in this paper. The synthesis of sulfobetaine surfactants was classified into three categories of single hydrophobic chain sulfobetaine surfactants, double hydrophobic chain sulfobetaine surfactants and Gemini sulfobetaine surfactants for review. Their application in TOR was classified into surfactant flooding, microemulsion flooding, surfactant/polymer (SP) flooding and foam flooding for review. The sulfonated betaine surfactants have good temperature resistance and salt tolerance, low critical micelle concentration (cmc) and surface tension corresponding to critical micelle concentration (γ_cmc), good foaming properties and wettability, low absorption, ultralow interfacial tension of oil/water, and excellent compatibility with other surfactants and polymers. Sulfobetaine surfactants with ethoxyl structures, hydroxyl and unsaturated bonds, and Gemini sulfobetaine surfactants will become an important direction for tertiary oil recovery because they have better interfacial activity in high-temperature (≥90°C) and high-salinity (≥10⁴ mg/L) reservoirs. Some problems existing in the synthesis and practical application were also reviewed.     

Preparation and Performance Evaluation of Fatty Amine Polyoxyethylene Ether Diethyl Disulfonate for Enhanced Oil Recovery in High‐Temperature and High‐Salinity Reservoirs

To enhance oil recovery in high‐temperature and high‐salinity reservoirs, a novel fatty amine polyoxyethylene ether diethyl disulfonate (FPDD) surfactant with excellent interfacial properties was synthesized. The interfacial tension (IFT) and contact angle at high temperature and high salinity were systematically investigated using an interface tension meter and a contact angle meter. According to the experimental results, the IFT between crude oil and high‐salinity brine water could reach an ultra‐low value of 10^?3 mN m^?1 without the aid of extra alkali at 90°C after aging. The FPDD surfactant has strong wettability alternation ability that shifts wettability from oil‐wet to water‐wet. The FPDD surfactant with a high concentration also has good emulsion ability under high‐temperature and high‐salinity conditions. Through this research work, we expect to fill the lack of surfactants for high‐temperature and high‐salinity reservoirs and broaden its great potential application area in enhanced oil recovery.