Guicai Zhang

Ultra-Low Interfacial Tension Between Heavy Oil and Betaine-Type Amphoteric Surfactants

Betaine surfactants with lipophilic groups of different lengths were synthesized in this research and the dynamic interfacial tension (IFT) between solutions of these surfactants and three kinds of crude oil from Shengli Oilfield are measured. The results indicated that, for Gudao and Gudong heavy oil, cetyl dimethyl hydroxyl sulfobetaine (SBET-16) was the most efficient in lowering the IFT in the case of no alkalis, while for Shengtuo heavy oil, cetyl dimethyl carboxymethyl betaine (CBET-16) was best. SBET-16 with the concentration of 0.003–0.1% and 0.005–0.1% can reduce the oil/water IFT to ultra-low for Gudao and Gudong oil respectively, CBET-16 with the concentration of 0.005–0.1% can lower the oil/water IFT to ultra-low for Shengtuo oil. These results showed that for different oils, an oil displacement agent with high capacity to lower the oil/water interfacial tension may be obtained only by changing the molecular structure of betaine surfactant. This study can be used to guide the design of surfactants for alkaline-free combination flooding.

Adsorption behavior of dodecyl hydroxypropyl sulfobetaine on limestone in high salinity water

Herein is presented a new methodology to determine the static adsorption of dodecyl hydroxypropyl sulfobetaine (DSB) on limestone with the use of HPLC. The results showed that with the increase of NaCl concentration, adsorption of DSB on the limestone surface decreased due to the increase of zeta potential (less negative). In contrast, with increasing CaCl2 concentration, adsorption of DSB decreased first and then increased, which corresponds to the change in trend of the limestone surface zeta potential. As to the influence of temperature, with an increase of temperature, the adsorption of DSB increased slightly. The behavior of DSB adsorption under different temperatures could be well interpreted by more adsorption of Ca2+ at higher temperature. It was also found that a little addition of inorganic salt could accelerate the formation of vesicles and more salt would inhibit the formation. By comparison of aggregation distribution before and after adsorption, it was found that micelles contribute more to adsorption than vesicles.

Influence of Oil Viscosity on Alkaline Flooding for Enhanced Heavy Oil Recovery

Oil viscosity was studied as an important factor for alkaline flooding based on the mechanism of “water drops” flow. Alkaline flooding for two oil samples with different viscosities but similar acid numbers was compared. Besides, series flooding tests for the same oil sample were conducted at different temperatures and permeabilities. The results of flooding tests indicated that a high tertiary oil recovery could be achieved only in the low-permeability (approximately 500 mD) sandpacks for the low-viscosity heavy oil (Zhuangxi, 390 mPa·s); however, the high-viscosity heavy oil (Chenzhuang, 3450 mPa·s) performed well in both the low- and medium-permeability (approximately 1000 mD) sandpacks. In addition, the results of flooding tests for the same oil at different temperatures also indicated that the oil viscosity put a similar effect on alkaline flooding. Therefore, oil with a high-viscosity is favorable for alkaline flooding. The microscopic flooding test indicated that the water drops produced during alkaline flooding for oils with different viscosities differed significantly in their sizes, which might influence the flow behaviors and therefore the sweep efficiencies of alkaline fluids. This study provides an evidence for the feasibility of the development of high-viscosity heavy oil using alkaline flooding.

Synthesis and Evaluation of Homogeneous Sodium Hexadecyl Polyoxypropylene Ether Sulfates

Sodium fatty alcohol polyoxypropylene ether sulfates and sodium fatty alcohol polyoxyethylene ether sulfates are nonionic–anionic surfactants, and this paper is devoted to study the synthesis and evaluation of this kind of surfactants. Using 1-bromhexadecane as raw material, homogeneous sodium hexadecyl polyoxypropylene ether sulfates (APS16-n, n = 1, 2, 3) were obtained through following steps: synthesizing hexadecyl polyoxypropylene ether alcohol by Williamson reaction, then esterifying with chlorosulfonic acid and neutralizing with sodium hydroxide. Homogeneous sodium hexadecyl polyoxyethylene ether sulfates (AES16-n, n = 1, 2, 3) were synthesized in the same way for comparison. The structures of these surfactants were identified by infrared spectroscopy, 1H-NMR analysis, and elementary analysis. The equilibrium interfacial tension between the aqueous surfactant solution and model oil (n-octane, n-decane and n-dodecane) were measured at different NaCl concentrations.

Improvement of Sweep Efficiency by Alkaline Flooding for Heavy Oil Reservoirs

Severe viscous fingering during water flooding of heavy oil leaves a large amount of oil untouched in the reservoir. Improving sweep efficiency is vital for enhancing heavy oil recovery. This study presented a laboratory study for improving sweep efficiency by alkaline flooding in heavy oil Reservoirs. This included glass-etched micromodel flooding tests, one-dimensional flooding experiments and three-dimensional physical model study. The micromodel tests show that W/O droplet flow plays a prominent role in the alkaline flooding to improve sweep efficiency. There is a minimum alkaline concentration that generates the W/O droplet flow, and the W/O droplet flow is more obvious with the alkaline concentration increasing. A series of flood tests were conducted using 325 mPa · s, 2000 mPa · s, and 3950 mPa · s heavy oils to assess the effectiveness of W/O droplet flow in alkaline flooding for enhanced heavy oil recovery. The flood tests results demonstrate the considerable potential for improved heavy oil recovery by alkaline flooding, and moreover, the incremental oil recovery has been found to increase as the alkaline concentration increases. The result obtained in three-dimensional physical model study indicates that the sweep area can be greatly improved by the formation of W/O droplet flow in alkaline flooding.

Dynamic Interfacial Tension Between Gudao Heavy Oil and Petroleum Sulfonate/HPAM Complex Systems

Abstract The dynamic interfacial tension between Gudao heavy oil and petroleum sulfonate/hydrolyzed polyacrylamide complex system was studied. It is shown that with the addition of hydrolyzed polyacrylamide into the solution of petroleum sulfonate, not only is the viscosity of the complex system increased, but also the dynamic interfacial tension is further lowered. Thus a complex system with high viscosity and low interfacial tension can be constituted by 0.3 wt% petroleum sulfonate and 0.18 wt% hydrolyzed polyacrylamide with a viscosity-averaged molecular weight of 1 × 107. In addition, the dynamic interfacial tension between complex system and crude oil can also be lowered by increasing the salt content in solution.

The Effect of Oil Viscosity, Permeability, and Residual Oil Saturation on the Performance of Alkaline Flooding in the Recovery of Heavy Oil

Abstract This article examines the effect of oil viscosity, permeability, and residual oil saturation on the performance of alkaline flooding to enhance heavy oil recovery. The results show that the in situ generated water-in-oil emulsion during alkaline flooding can effectively improve sweep efficiency and, consequently, improve heavy oil recovery. The tertiary oil recovery can reach over 20% of the initial oil in place using 1.0% NaOH. The incremental oil recovery of alkaline flooding increases with the residual oil saturation. However, the tertiary oil recovery gradually increases with decreasing the permeability. But the effectiveness of alkaline flooding does not decrease with the increasing oil viscosity.

Branch Fractures in Oriented Hydraulic Fracturing, Modeling, and Experiments

A three-dimensional finite element model is established to study factors influencing factures in oriented hydraulic fracturing. The results indicate factors include horizontal principal stress difference and the angle between oriented perforation and the maximum horizontal stress. The computations reveal that hydraulic fracture will not always initiate along a perforation, and usually the hydraulic fracture is in a zigzagged shape. When the stress difference and the perforation angle are great, dual fractures will appear along both perforation and the maximum stress directions, verified by laboratory experiments. For improving the accuracy of stress measurement, oriented perforation can reduce the complexity of hydraulic fractures.

Laboratory Studies of Depressurization with a High Concentration of Surfactant in Low-Permeability Reservoirs

To solve the problem of high pressure of water injection in low permeability reservoirs, a high concentration of surfactant system was developed in this article. With the solubilization of oil in aqueous surfactant solution as a criterion, a formula was screened from anionic and nonionic-anionic surfactants, and the optimal depressurized system was obtained as follows, 13.3% surfactant HEX +2.23% n-propanol +4.47% n-butanol, the solubilization capability being up to 0.66 g/g. This system had good salt tolerance, and it exhibited water external microemulsion in the range of of 1 to 200 g/L NaCl. Core flooding results show that this high concentration of surfactant system formed water external microemulsion with the residual oil in the core, reducing the displacement pressure over 35%. Meanwhile, the effects of concentration and injection volume on depressurization were also investigated. It is indicated that a good depressurization effect was achieved after injecting 1 pore volume of the system with the salt concentration of 100 g/L.

Effect of Organic Acid on Lauroamide Propyl Betaine Surface Dilatational Modulus and Foam Performance in a Porous Medium

ABSTRACT The purpose of this work was to study the effect of surface tension and surface dilatational modulus on foam performance in high-salinity water in a porous medium. In order to clarify the role of the surface dilatational property in foam flow in a porous medium, three systems were established: a system with low surface dilatational modulus and high surface tension, a system with low surface dilatational modulus and low surface tension, and a system with high surface dilatational modulus and low surface tension. Measurement of dilatational modulus and surface tension showed that lauroamide propyl betaine (LAB) could not reduce surface tension and that surface dilatational modulus was low. The addition of lauric acid (LCOOH) to LAB could not achieve high surface dilatational modulus; however, it could reach lower surface tension. The addition of myristic acid (MCOOH) to LAB could achieve high surface dilatational modulus and lower surface tension. Unlike the other two systems, the results of a dilatational modulus comprised of a mixture of MCOOH and LAB were not a constant, as demonstrated by varied surface area deformation outcomes. With the increase of deformation, surface dilatational modulus decreased. Results of foam flow tests showed that among the two lower surface dilatational modulus systems, LAB foam had higher flow resistance regardless of flow rate. Among the two systems of similar lower surface tension, the mixture of LAB and MCOOH showed higher flow resistance than the mixture of LAB and LCOOH. However, with the increase of flow rate, pressure differences between the two systems became smaller, which corresponded to the decrease of surface dilatational modulus with an increase of deformation. GRAPHICAL ABSTRACT