Lessons Learned from Our Recent Research in Chemical Enhanced Oil Recovery (C-EOR) Methods

As a result of the ever-increasing global energy demand coupled with the rapid decline of the oil production, the games of enhanced oil recovery (EOR) are played in many oilfields worldwide especially in China. It was reported that EOR jobs produced 45.1 × 104 m3/d of oil production rate in 2014 all over the world, proving the significance of these jobs. Due to the complex geology, chemical enhanced oil recovery (C-EOR) methods are considered the predominant technology in China and takes nearly 86% of the total EOR projects currently. This fact motivates us to develop novel and more advanced C-EOR methods for different geological types of Chinese reservoirs such as high temperature and pressure, ultralow permeability, heavy oil reservoirs, etc. Through 20 years’ efforts, many advantageous C-EOR methods have been successfully developed in our group and tested in oilfields such as stabilized foam injection, nanofluid flooding, functional polymer flooding, etc. Herein, this chapter summarized the latest experimental results of three representative C-EOR methods. More attentions were given to the relationship between bulk properties and flow behaviors in porous media. The lessons learned from our research in C-EOR were also discussed in this chapter

Combustion Behavior and Kinetics Analysis of Isothermal Oxidized Oils from Fengcheng Extra-Heavy Oil

The low-temperature oxidation (LTO) of heavy oil is of great significance for the combustion front stability, which directly influences the efficiency and safety of in-situ combustion (ISC). To provide feasible heating by artificial ignition before the implementation of ISC in the Xinjiang Fengcheng (FC) oilfields, this paper investigates the oxidation behavior of FC extra-heavy oil and its isothermal oxidized oils. Firstly, FC extra-heavy oil was subjected to isothermal oxidation experiments conducted utilizing an oxidation reactor, and the physical properties of the gaseous products and oxidized oils were analyzed. The combustion behavior of the FC extra-heavy oil and oxidized oils was then studied by non-isothermal thermogravimetry and differential scanning calorimetry. Subsequently, the Friedman and Ozawa–Flynn–Wall methods were adopted to perform kinetic analysis. Oxygen consumption was always greater than the production of CO and CO2, so oxygen addition reactions were the main pathway in heavy oil LTO. H/C decreased to 8.31% from 20.94% when the oxidation temperature rose from 50 °C to 150 °C, which deepened the oxidation degree. The density and viscosity of 200 °C to 350 °C oxidized oils increased at a slower rate, which may be related to the LTO heat effect. The change law of temperature interval, peak temperature, and mass loss of the oxidized oils had a good correlation with the static oxidation temperature. Compared with other oxidized oils, the peak heat flow and enthalpy of 350 °C oxidized oil increased significantly with high-temperature combustion, and were 42.4 mW/mg and 17.77 kJ/mol, respectively. The activation energy of 350 °C oxidized oil began to decrease obviously around a conversion rate of 0.4, which indicates that it was beneficial to coke deposition with stronger activity. Finally, we came up with LTO reaction mechanisms and put forward a reasonable preheating temperature for the application of ISC in FC oilfields

In-situ heavy oil upgrading by high temperature oxidation through air injection

Air injection has been widely considered as a technology to enhanced heavy oil recovery on account of the heavy oil upgrading caused by high temperature oxidation during this process. This paper aims at exploring the effects of oxidation thermal processing in a porous media at high temperature from 500 to 540℃ which is the high temperature oxidation range of heavy oil known from TG results, and reaction time from 8 to 16 hours for heavy oil upgrading. It was suggested that the viscosity decreased with the temperature and retention time increased due to getting less ring structure seen from IR Spectrum results. It was observed that the viscosity of heavy oil was reduced 1 to 2 orders of magnitude. Besides, the kinetics of heavy oil upgrading were analysed using five pseudo components including HO (C35+), MO (C15 ~ C35), LO (C5 ~ C14), coke, G (gas products) and successfully predicted the products results with an error of 4.34%, and great correlation to Arrhenius equation. The activation energies obtained are in the range of 44 ~ 215 kJ/mol. This work has great value in revealing the mechanisms of high temperature oxidation heavy oil upgrading and assisting heavy oil production

Preparation and Properties of Polymer/Vermiculite Hybrid Superabsorbent Reinforced by Fiber for Enhanced Oil Recovery

A series of polymer/clay hybrid superabsorbent composites (SACFs) comprising acrylamide, acrylic acid, sodium 2-acrylamido-tetradecyl sulfonate, fiber, and vermiculite by in situ intercalation and exfoliated method was successfully synthesized. The structure of SACFs was characterized by IR, SXRD, and SEM measurements. Much notable absorbency for SACF-2 was observed compared to that for SACF-1 in the absence of hydrophobic group in the high cationic solution due to the alkyl carbon chain and sulfonic acid group of hydrophobic moistures protecting the cations from attacking the carboxylate groups. What is more, high temperature fiber which acts as bridge connection for the polymeric network structure enhanced both toughness and strength for SACF-4 in the harsh conditions. At the total dissolved substance of 212000 mg/L for Tarim Basin injected water and the temperature of 120°C, desired absorbency as well as water retaining property for SACF-4 was observed during the long period of thermal ageing. Core flooding experiments demonstrated that SACFs could migrate as amoeba in the porous medium and accumulated in the narrow channel to adjust injection profile, promoting the subsequent water diverting into the unswept zones. Finally, characteristic parameters for SACFs calculated from flooding experiment further confirmed these polymer/clay hybrid composites reinforced by fiber would have robust application in the mature oilfield for profile control

Experimental Investigation into the Oxidative Characteristics of Tahe Heavy Crude Oil

The thermal method of in-situ combustion (ISC) was proposed to produce Tahe heavy oil; therefore, the oxidative characteristics of this oil are critical, especially its coking behaviors, which are closely related to the combustion process. In this work, a series of thermogravimetric and differential scanning calorimetry (TG-DSC) tests with isothermal and non-isothermal models were conducted to determine the oxidative characteristics of Tahe heavy oil. Moreover, the morphology of the produced cokes was observed with a scanning electron microscope (SEM). The results showed that the heavy oil was partially coked due to high-pressure oxidation, and these cokes were significantly more active than the heavy oil, leading to noticeable heat release at low temperatures. Higher-temperature oxidation involved compounds in the coking and thus required more time to initiate the reactions. A significant reduction of the elements (S, H, N) was observed in higher-pressure oxidation, and the porous morphology of the coke was created. Increasing the oxidation pressure led to higher-porosity cokes and subsequently enhanced the reaction of oil and air. The particle structures generated by oxidation reactions on the surface of oxidized coke can be consumed by the combustion process

Numerical simulation of mechanism of high-pressure air injection (HPAI) in light oil reservoirs

Based on the research progress of the crude oil oxidation-combustion model proposed by predecessors, this paper established a new multi-reaction model for high-pressure air injection (HPAI) process to compare the HPAI performance in reservoirs without water injection and high water cut reservoirs by numerical simulation. Results show that gas override is universal in air injection in light oil reservoirs before and after waterflooding, and is more apparent in strongly heterogeneous reservoirs. However, the produced oxygen concentration is very low all the time. For reservoirs that haven't gone through water injection, at high air injection rate oil is very likely to auto-ignite and keep high peak temperature and long time stable combustion front. However, there exists a critical value for the influence of air injection rate on the combustion front moving speed, above the critical value, oil recover factor increment is not obvious with the increase of air injection rate. At the same air injection rate, high water cut reservoirs are 6.3% lower in recovery factor than reservoirs without water injection, With high increase in GOR and high water recovery degree during HPAI process. It is suggested that polymer gel/ and or foam assisted air injection be taken to reduce GOR/ and or water cut in production wells. Key words: air injection, light oil reservoirs, reservoirs without water injection, high water cut reservoir, gas override, numerical simulation, mechanism stud

Viscosity Reduction Behavior of Carbon Nanotube Viscosity Reducers with Different Molecular Structures at the Oil–Water Interface: Experimental Study and Molecular Dynamics Simulation

Effectively enhancing oil recovery can be achieved by reducing the viscosity of crude oil. Therefore, this paper investigated the viscosity reduction behavior of carbon nanotube viscosity reducers with different molecular structures at the oil–water interface, aiming to guide the synthesis of efficient viscosity reducers based on molecular structure. This study selected carbon nanotubes with different functional groups (NH2-CNT, OH-CNT, and COOH-CNT) for research, and carbon nanotubes with varying carbon chain lengths were synthesized. These were then combined with Tween 80 to form a nanofluid. Scanning electron microscopy analysis revealed an increased dispersibility of carbon nanotubes after introducing carbon chains. Contact angle experiments demonstrated that -COOH exhibited the best hydrophilic effect. The experiments of zeta potential, conductivity, viscosity reduction, and interfacial tension showed that, under the same carbon chain length, the conductivity and viscosity reduction rate sequence for different functional groups was -NH2 2. With increasing carbon chain length, conductivity and interfacial tension decreased, and the viscosity reduction rate and the dispersing and stabilizing ability increased. Molecular dynamics simulations revealed that, under the same carbon chain length, the diffusion coefficient sequence for different functional groups was -NH2 < -OH < -COOH. The diffusion coefficient gradually decreased as the carbon chain length increased, resulting in better adsorption at the oil–water interface. This study holds significant importance in guiding viscosity reduction in heavy oil to enhance oil recovery

Characteristics of Viscoelastic-Surfactant-Induced Wettability Alteration in Porous Media

Wettability alteration is one of the most important mechanisms of surfactant flooding. In this work, the combined Amott/USBM (United States Bureau of Mines) method was applied to study the average wettability alteration of initially neutral cores after viscoelastic-surfactant (VES) filtration. The effects of static aging, dynamic aging, VES concentration, filtration flow rate, and pore radius on the alteration of a core’s average wettability were studied. The wettability-alteration trends measured by Amott and USBM were consistent, demonstrating that the overall hydrophilicity of the core was enhanced after VES filtration. The wettability alterations of the core brought about by dynamic aging were more significant than by static aging. The viscoelastic properties of the VES played an important role in altering the wettability. In addition, the ability of the VES to affect the core’s wettability was significantly enhanced when the VES concentration was increased, which was beneficial in increasing VES adsorption on the pore-wall surface, thus altering the overall wettability of the core. Increasing filtration flow rates can destroy those high-viscosity VES aggregates via the higher shear rate. A higher retention of VES makes the core more hydrophilic. The difference in the wettability of cores with different pore radius after VES filtration was not significant. The alteration of average wettability caused by VES in porous media provides a new vision for studying the EOR mechanism of VES