Wanfen Pu

High temperature and oil tolerance of surfactant foam/polymer–surfactant foam

Foam performance during oil displacement is closely related to the reservoir environment. In this study, both bulk and porous media experiments were conducted to investigate surfactant foam and polymer–surfactant foam behaviors at high temperature and with crude oil. After aging at 90 °C for 90 days, the foam drainage half-life of the aged polymer–surfactant foam was four times longer than that of the fresh surfactant foam. Scanning electron microscope images indicated that, even experienced high temperature aging, the polymer and surfactant could still develop multilayer complexes to enhance the foam film strength. Within a certain oil content, the foam stability in the presence of oil could be better than in the absence of oil. Stereoscopic microscope images revealed that the existing form and content of oil in the foam film had played a vital role. Core flooding experiments further confirmed that stable surfactant foam and polymer–surfactant foam could generate in the presence of waterflooded residual oil and give rise to additional oil recovery of 15.35% and 35.75% at 90 °C, respectively. The positive responses of this study may be attractive to potential foam field applications.

Stability, CO2 sensitivity, oil tolerance and displacement efficiency of polymer enhanced foam

This paper focuses on the benefits of polymers that contribute to foam flooding, such as foam stability, carbon dioxide (CO2) sensitivity, oil tolerance and displacement efficiency. From the results, polymer enhanced foam was found to have a high stability and an insignificant coalescence mainly because of the high viscous force and strong foam films. Some significant improvements of foam properties were observed in the polymer enhanced CO2 foam, especially in a supercritical state (16xa0MPa, 90 °C), and polymer enhanced foam showed remarkable oil tolerance because of the fact that the stable emulsion was uniformly dispersed in liquid films. Furthermore, polymer enhanced foam could promote mobility control and increase the liquid division and enhanced oil recovery in a strong heterogeneous formation.

Effects of interfacial tension and emulsification on displacement efficiency in dilute surfactant flooding

This study provides an investigation on the effect of interfacial tension (IFT) and emulsification on displacement efficiency in dilute surfactant flooding. In previous studies, usually the surfactant concentration or type was changed to achieve different IFT levels. However, in this study, only one surfactant with a constant concentration of 0.2 wt% was used to obtain five surfactant formulations with different IFT levels of 101, 10−1, 10−2, 10−3, and 10−4 mN m−1 by changing the salinity of the salt water to eliminate the influence of the surfactant concentration or type. The emulsifying rates of the five surfactant formulations were measured. The emulsion stability was evaluated by measuring the backscattering and transmission light using a Turbiscan LAB. It turned out that the five surfactant formulations had a unique characteristic that their emulsifying ability successively decreased with the reduction of the IFT. These five surfactant formulations were used to evaluate the effect of the IFT and emulsification on the displacement efficiency by core flooding experiments. The results indicated that the obtained additional displacement efficiency decreased with the increase of the emulsification ability but increased with the reduction of the IFT, which confirms that the lower the IFT, the higher the displacement efficiency in dilute surfactant flooding. Simultaneously, the reduction of the IFT might have a more important role on improving displacement efficiency for residual oil after water flooding than emulsification since the additional displacement efficiency decreased with the increase of emulsification.

Influences of structure and multi-intermolecular forces on rheological and oil displacement properties of polymer solutions in the presence of Ca2+/Mg2+

Salinity-tolerance is one of the crucial factors determining the applicability of a polymer in Enhancing Oil Recovery (EOR) process. In the current study, the rheological and oil displacement properties of four types of polymers with similar structures, including a comb polymer (KYPAM), a double tailed hydrophobic associating polymer (DTHAP), a comb hydrophobic associating polymer (CHAP) and a comb micro-block hydrophobic associating polymer (CBHAP), were comprehensively investigated. The experimental results proved that the thickening ability and salt resistance of the polymer was not significantly improved if only one intermolecular force functioned. On the contrary, multi-intermolecular forces, such as hydrophobic association and complexation, rendered a synergistic effect in the polymer solutions, through which the thickening property, salt resistance particularly Ca2+/Mg2+ resistance, and also the elasticity of the polymers were noticeably promoted. In oil displacement experiments, the EOR factors improved by CBHAP and CHAP can reach 27.1% and 18.8%, which were much higher than that of KYPAM (11.5%) and DTHAP (11.7%).

A gel-like comb micro-block hydrophobic associating polymer: Synthesis, solution property and the sol-gel transition at semi-dilute region

The gel-like comb micro block hydrophobic associating polymer (CBHAP) was synthesized by mixed micellar polymerization. The chemical structure of the copolymer was characterized by Fourier transform infrared spectroscopy (FT-IR). The rheological properties of CBHAP in fresh water and saline water at semi-dilute region were investigated. The experimental results show that, because of the intermolecular forces, shear thickening phenomenon can be observed obviously in brine solution and the Newtonian viscosity plateau could be observed clearly before 40 s-1. When the concentration reaches 3,000 mg/L, the G’ and G” becomes stable, indicating that CBHAP experiences the sol-gel transition after 3,000 mg/L. However, the curl structure is formed by adding salt, resulting in a higher concentration of the sol-gel transition than that in fresh water. Once the curl structure is destroyed by shearing or stretching, the intermolecular forces will take into effect and complete the sol-gel transition at semi-dilute region.

Utilisation of multiple gas injection to enhance oil recovery for fractured-cavity carbonate heavy oil reservoir

Gas injection has been proven to be a valuable enhanced oil recovery (EOR) process for light oil reservoirs and ordinary heavy oil reservoirs, but it was rarely proposed as an EOR process for fractured-cavity carbonate heavy oil reservoir. This study aims to investigate the feasibility of the gas injection based on flooding and cycle stimulation method with respect to enhancing oil recovery for fractured-cavity carbonate heavy oil reservoir. Thus, a representative physical model of core was designed, and some gas flooding and cyclic gas stimulation experiments were conducted. The experimental results show that gas injection can enhance the oil recovery in fractured-cavity carbonate reservoir and carbon dioxide is the optimal injected gas in this study. Also, gravity drainage plays an important role in fractured-cavity carbonate reservoir besides the various recovering mechanisms in conventional reservoir. In addition, Tahe heavy oil has a strong capacity of oxygen consumption due to the high content of polar compound. [Received: May, 1, 2015; Accepted: February 29, 2016]

Study of the catalytic effect of copper oxide on the low-temperature oxidation of Tahe ultra-heavy oil

The heavy metal compounds existing in a reservoir have a significant catalytic effect on the low-temperature oxidation of heavy oil during the in situ combustion (ISC) process. This study focused on the thermal behavior of Tahe ultra-heavy oil and the catalytic effect of copper oxide on low-temperature oxidation to probe into the applicability of the ISC technique. For this purpose, three samples, including Tahe crude oil, oxidized oil and oxidized oil-CuO, were studied by performing thermogravimetry (TG)/derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) with three different heating rates (5–10 and 15xa0°Cxa0min−1) at temperatures ranging from 30 to 830xa0°C. The result indicated that more fuel was produced to cause more exothermic heat in the high-temperature oxidation (HTO) zone as the heating rate increased. Kinetic parameter calculation detected that the activation energy of the crude oil was 13.73xa0kJxa0mol−1 in the low-temperature oxidation (LTO) stage and 131.72xa0kJxa0mol−1 in the HTO stage, respectively. Compared with TG/DSC analysis and the activation energy of the three samples, the activation energy of oxidized oil was reduced obviously in the HTO zone by the crude oil. Additional CuO accelerated fuel deposition in the low-temperature region with no reduction in the activation energy, revealing that CuO has a catalytic effect on Tahe crude oil to cause fuel deposition in LTO. Based on the comprehensive thermal performance and kinetic characterization of the crude oil, 69.61% of the crude oil remained in the final LTO, which can be oxidized as coke to supply sufficient fuel for the HTO stage. This finding indicates that the ISC technique may be feasible for Tahe oilfield development.

Application potential of in situ emulsion flooding in the high-temperature and high-salinity reservoir

Abstract In this research, an emulsifier formulation named SC-18 for W/O system was screened out and evaluated for feasible application of in-situ emulsion flooding in high-temperature and high-salinity reservoir. Results showed that SC-18 could reduce interfacial tension to 10–2 order of magnitude and change rock wettability from oil-wet to water-wet, which was beneficial to decrease residual oil saturation and improve displacement efficiency. Meanwhile, rheological testing showed that emulsion produced by SC-18 exhibited good temperature tolerance and mechanical stability, which favored mobility control and sweep efficiency enhancement under harsh conditions. In addition, good viscoelasticity of produced emulsions could also improve sweep efficiency by strengthening plugging and diverting effects of emulsion droplets, namely enhancing “Jiamin effects.” By means of natural core flooding and visualized plate model, it was proved that in-situ emulsion flooding with SC-18 could improve both displacement efficiency and sweep efficiency for high-temperature and high-salinity reservoir. GRAPHICAL ABSTRACT

Investigation on stabilization of foam in the presence of crude oil for improved oil recovery

Abstract A major concern, in the foam flooding projects, is the stability of foam in the presence of oil. In this study we chose three foaming agents with different behaviors in the oil-bearing environments and examined their performance in terms of the emulsified oil and the pseudoemulsion films. The results indicate that the state of the emulsified oil or the pseudoemulsion films has a significant impact on foam stability. Two hypothesizes suggest that the role of emulsified oil played in foam stabilization can be summarized as increasing the emulsion stability and creating the viscous liquid phase, and interfacial adsorption and viscoelastic layers of pseudoemulsion films present a strong correlation with the foam stability. From the foam flooding experiments, the oil-enhanced foam is deemed to be more efficient in the oil displacement and the liquid diversion. Graphical Abstract

Stability and adsorption of multiphase foam system with high temperature resistance

ABSTRACT The multiphase foam system with high temperature resistance mainly consisted of the foaming agent (0.3% disodium monoester succinate (DMS)) and the foam stabilizer (0.2% PS4 and 0.5% hydrophilic SiO2). The synergy between polysaccharide (PS4) and SiO2 was determined by the foam composite index (Fc), which remained at a higher level after aging for 30 days at 115 °C. Macro and micro structure of foam in the presence or absence of SiO2 was observed with the naked eye and a scanning electron microscope (SEM), respectively; the result confirmed that SiO2 could adsorb on a liquid film. In addition, the effects of crude oil components and pressure on foam properties were investigated; the latter was monitored by a visualized reactor, and the results showed that asphaltene and high pressure boosted foam while it was opposite to aromatic hydrocarbon. Moreover, the static and dynamic adsorption of DMS under different conditions were determined, and the results could be concluded that besides external factors, PS4 could reduce the adsorption of DMS effectively. GRAPHICAL ABSTRACT