Qingfeng Hou

Current development and application of chemical combination flooding technique

Abstract Great progress and success have been achieved in the fundamental study and field test of chemical combination flooding in recent years. In China, a low concentration ASP formula is employed to achieve ultra-low interfacial tension by the synergistic effect of alkali and surfactant. The viscosity of polymer solution prepared from produced water can meet the technological requirement when salt tolerance polymer is applied. ASP or SP flooding can increase both oil displacement efficiency and sweep volume. ASP pilot tests and industrial field tests in Daqing Oilfield have resulted in an oil recovery increase of 18.5%-26.5%. The chemical combination flooding has entered into the industrial promotion and application stage, with a series of supporting techniques formed in the field tests. The main challenges in this technique include short pump-checking period and difficulty in produced liquid handling and high cost. Micelle-polymer flooding as the major chemical combination flooding technique was applied abroad in the early stage of chemical flooding tests. However, the micelle-polymer flooding has not been applied widely due to its high cost. With the rise of oil price in recent years, low concentration chemical combination flooding has drawn more attention. Because of high temperature and high salinity in most reservoirs abroad where chemical combination flooding is used, high performance temperature and salt tolerance oil displacement agents are the bottleneck for future chemical flooding.

Stability Comparison Between Particles-Stabilized Foams and Polymer-Stabilized Foams

The enhanced oil recovery (EOR) results of foam flooding depend largely on the stability of foam flow within porous reservoirs. To stabilize foams, polymers such as partially hydrolyzed polyacrylamide are often introduced into the foaming agent. However, particles-stabilized foams have been paid more attentions in recent years. To investigate the better stabilizer for foam application in EOR, experimental stability comparison between polymer-stabilized foams and clay particles-stabilized foams was investigated. To do this, the static stability of bulk foams was studied by half-life of foams and rheological behavior of foaming agent solution. The dynamic stability of two types of compressed foams in porous media was then compared with blocking ability. Results showed that particles-stabilized bulk foams were more stable than polymer-stabilized bulk foams, and the viscoelasticity of surfactant-particles solution was higher. Moreover, blocking ability of particles-stabilized foams was also better than that of polymer-stabilized ones.

Effect of oil on the stability of polymer enhanced foams

The enhanced oil recovery (EOR) results of foam flooding depend largely on the stability of foam flow within reservoirs in the presence of crude oil. Experimental studies indicated that oil would impact the foam stability greatly. This paper discussed the effect of oil on the stability of polymer enhanced foams. Two commercial polymers including hydrolysed polyacrylamide (HPAM) and modified polyacrylamide (MPAM) were employed. Mechanism on interaction between foam and oil for experimental foam systems was also studied quantitatively based on several physical-chemical parameters including spreading coefficient, entering coefficient, bridging coefficient and lamella number. The foam stability could be remarkably improved with both HPAM and MPAM. The effect of oil on the stability of polymer enhanced foams could not be fully understood by related coefficient theories. The increase in viscoelasticity of foam films would play a key role in the stability improvement for polymer enhanced foams.

Feasibility Studies on CO2 Foam Flooding EOR Technique After Polymer Flooding for Daqing Reservoirs

Most of the high permeability reservoirs in the Daqing Oil Field have been conducted by water flooding and polymer flooding. Further development of such mature reservoirs has become a big challenge due to highly dispersed residual oil. Foam flooding, as a candidate enhanced oil recovery (EOR) technique, has been proposed. In this article, EOR evaluation of CO2 foam flooding after polymer flooding has been conducted on homogeneous sandpack cores flooding tests at the reservoirs condition. Results indicated that CO2 foam flooding could enhance considerable oil recovery, even if the oil recovery occurs after polymer flooding. It was also found that higher quality foam with higher pressure gradient could improve larger swept volume and, thus, recovered more residual oil than lower quality foam did. The influence of both the injection strategy and solubility of CO2 in brine on EOR of CO2 foam flooding was also studied. GRAPHICAL ABSTRACT

On the Origin of Foam Stability: Understanding from Viscoelasticity of Foaming Solutions and Liquid Films

The foam stability (drainage half-life) of α-olefin sulfonate (AOS) with partially hydrolyzed polyacrylamide (HPAM) or xanthan gum (XG) solution was evaluated by the Warring Blender method. With the increase of polymer (HPAM or XG) concentration, foam stability of the surfactant–polymer complexes increased, and the drainage half-life of AOS-XG foam was higher than that of AOS-HPAM foam at the same polymer and surfactant concentration. With the addition of polymer (HPAM or XG), the viscoelasticity of bulk solution and the liquid film were enhanced. The viscoelasticity of AOS-XG bulk solution and liquid film were both higher than that of AOS-HPAM counterparts.

Blocking Ability and Flow Characteristics of Nitrogen Foam Stabilized with Clay Particles in Porous Media

Particles-stabilized foams have received more attention in recent years due to their specific characteristics and advantages in contrast to conventional foams which were stabilized with surfactants. However, the rheology of particles-stabilized foam in consolidated cores was rarely studied. To investigate the feasibility of the particles-stabilized foam application in enhanced oil recovery, the blocking ability and flowing characteristics of foam stabilized with clay particles were investigated by using experimental cores. To do this, the foam resistance factor was studied as an index in this article. The effects of foam quality (gas velocity divided by total velocity), injection rate of foam, and the permeability of cores on the blocking ability of foams were investigated. Results showed that the blocking ability reached the peak value at the foam quality of 0.74. This indicated effective blocking ability as conventional foams performed in porous media. Moreover, the foams block the channels more effectively in high permeability cores, compared with low permeability ones. Finally, foams displayed shear-thinning property in porous media as injection rate increased.

Synthesis and performance evaluation of novel alcohol ether carboxylate surfactants for alkali-surfactant-polymer flooding

Novel surfactants alcohol polyoxypropylene polyoxyethylene ether carboxylates (APPEC) were successfully synthesised by carboxymethylation reaction of alcohol polyoxypropylene polyoxyethylene ether (APPE) to meet alkali-surfactant-polymer (ASP) flooding needs. The structure of APPEC was characterised by Fourier transform infrared (FTIR) spectrometry. The reaction conditions of APPEC including reaction ratio of raw materials, temperature and reaction time were optimised. Interfacial tension and ASP core flooding experiments were also carried out to evaluate the enhanced oil recovery (EOR) performance of the APPEC surfactants. The interfacial tension between Xinjiang crude oil and synthetic water could be decreased to ultra-low level in a short time with 0.4 wt% APPEC at 28.7°C. Two core flooding experiments proved that ASP flooding system could improve the oil recovery by 21.5% or 22.3%. Therefore, the APPEC surfactant formulas could improve oil displacement efficiency under Xinjiang reservoir condition.

Comparative Study of Extensional Viscoelasticity Properties of Liquid Films and Stability of Bulk Foams

The extensional viscoelasticity modulus and conductivity of liquid films and stability of bulk foams were investigated respectively. The effects of sinusoidal exciting frequency, polymer type, and polymer concentration on liquid film viscoelasticity modulus were systematically discussed. Higher film viscoelasticity modulus could be assigned for FS01/MPAM film systems than for FS01/HPAM ones. The film conductivity result showed that FS01/HPAM or FS01/MPAM liquid film systems could delay the liquid drainage speed under dynamic conditions compared with FS01 ones. Bulk foam test based on Waring Blender method indicated that FS01/HPAM foam was more stable than FS01/MPAM. Compared with static bulk foam test, the extensional viscoelasticity and conductivity method could reflect the dynamic behavior of liquid films.