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This paper systematically investigated the progress of laboratory research and field application of biochemical composite enhanced oil recovery technology in the past 10 years in China and abroad. The synergistic mechanism between oil recovery bacteria， biosurfactants， biopolysaccharides， and chemical oil recovery agents such as surfactants， polymers， and nanoparticles was discussed in terms of improving displacement efficiency and expanding swept volume， respectively. In addition， the system construction and field application effects were analyzed. The results show that the combination of biological bacteria and their metabolites with chemical oil recovery agents has synergistic effects on interfacial tension reduction， emulsification dispersion， mobility ratio control， and viscosity reduction of heavy oil， and the field application has achieved good application results. Bacteria polymer composite profile control and microbial desulfurization and viscosity preservation technologies were explored in Shengli Oilfield， and estimated recoveries reached 9% and 10.3%， respectively. Biological ASP composite technology was applied in Daqing Oilfield， and the recovery of the pilot area has been improved to 22%. The biochemical composite enhanced oil recovery technology has great potential for application in the exploitation of difficult-to-recovery reserves in mature oilfields. The next step is to continue to deepen the synergistic mechanism between biological and chemical systems， innovate the integration and implementation process of biological and chemical oil recovery systems according to the differences between reservoir planes and inter- and intra-layers， refine the implementation plan for different development stages and reservoir spaces， and maximize the advantages of biological and chemical synergistic efficiency enhancement technologies through the three-dimensional balanced development of reservoirs to satisfy the demand for sustainable development of mature oilfields.

Sphingan is a crucial exopolysaccharide (EPS) produced by Sphingomonas genus bacteria with wide-ranging applications in fields such as food, medicine, and petroleum. In this study, a novel sphingan, named MT gum, was overproduced from the wild-type strain Sphingomonas sp. MT01 at a yield of 25.6 g/L in a 5 L fermenter for 52 h at 35 °C. The MT gum was mainly composed of D-glucose (65.91%) and L-guluronic acid (30.69%), as confirmed by RP-HPLC, with Mw 7.24 × 105 Da. The MT gum exhibited excellent rheology and pseudoplasticity characteristics while maintaining function in high-temperature and high-salinity environments. The viscosity retention rates of MT gum (0.1%, w/v) were 54.06% (80 °C, 50,000 mg/L salinity) and 34.78% (90 °C, 50,000 mg/L salinity), respectively. The apparent viscosity of MT solutions (0.1%, w/v) was much higher than that of welan solutions under the same conditions. The MT gum also had the property of instant dissolution and completely swelled in 40 min. Meanwhile, the MT gum was resistant to 3–10 mg/L Fe2+ in the reservoir conditions, ensuring its application in offshore oil fields. These findings suggested that the biopolymer MT gum produced by the strain MT01 had significant potential in enhanced oil recovery (EOR) of high-temperature and high-salinity oil reservoirs. [ABSTRACT FROM AUTHOR]

Weathered crust karst reservoirs with intricately interconnected fractures and caves are common but challenging enhanced oil recovery (EOR) targets. This paper investigated the remaining oil distribution rules, formation mechanisms, and EOR methods through physical experiments on acrylic models resembling the geological features of weathered crust reservoirs. Acrylic models with precision dimensions and morphologies were fabricated using laser etching technology. By comparing experiments under different cave filling modes and production well locations, it was shown that a higher cave filling extent led to poorer bottom water flooding recovery due to stronger flow resistance but slower rising water cut owing to continued production from the filling medium. Multi-well water and gas injection achieved higher incremental oil recovery by alternating injection–production arrangements to establish new displacement channels and change drive energy. Gas injection recovered more attic remaining oil from upper cave regions, while subsequent water injection helped wash the residual oil in the filling medium. The findings reveal the significant effects of fracture cave morphological configuration and connectivity on remaining oil distribution. This study provides new insights and guidance for EOR design optimization catering to the unique features of weathered crust karst fractured vuggy reservoirs. [ABSTRACT FROM AUTHOR]

Silicon Oxide nanoparticle (SiO2-NP) with appropriate surface functionalization has tremendous potential in enhanced oil recovery (EOR) via wettability alternation, interfacial tension reduction, disjoining pressure enhancement, electric charge modification, etc. Prior to the application of SiO2 to EOR, an effective functionalization and an accurate characterization of the surface properties are indispensable. Though many experimental works have been performed in this area, a systematic review is still lacking. Therefore, a review of the above content is presented. Current research gaps are identified, and future outlooks are indicated. This review provides guidance for SiO2-NP surface functionalization, characterization, and evaluation. [ABSTRACT FROM AUTHOR]

BACKGROUND Surfactin, a lipopeptide biosurfactant produced by Bacillus strains, is one of the most surface-active biosurfactants, and has the potential to enhance oil recovery or environmental remediation. However, low yield and high production costs limit its use in high-volume applications. In this work, Bacillus subtilis BS-37 was immobilized on a piece of cotton towel in a 5 L stirred tank reactor; the fill-and-draw process and foam fractionation were used for repeated batch fermentations. A two-stage pH control operation was developed for surfactin fermentation: for repeated batch fermentation, the pH value was 5.0 for the biomass accumulation in the previous 6 h; and then the pH value was raised to 7.5 for surfactin production over the following 18 h of fermentation. RESULTS The immobilized Bacillus subtilis BS-37 cells were efficiently reused for 7 cycles, producing 7887.3 mg surfactin in total. CONCLUSIONS The repeated batch fermentation, low-cost foam fractionation, reusable immobilized cells, and energy-efficient open (nonsterile) fermentation could greatly promote the development of industrial production of surfactin. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

To study the effect of the osmotic stress in the microenvironment on the growth and metabolism of the encapsulated cells under aerobic condition, Osmo-sensitive yeast Y02724 and high-osmotic resistant yeast Hansel were used as models to explore the growth and metabolism state of the cells cultivated inalginate-chitosan-alginate (ACA) microcapsules. The changes of the yeast cells' specific growth rate, maximum product quantity and the secretion of ethanol and glycerol were analyzed. For Y02724, the yield of ethanol was increased in the ACA microenvironment compared to suspension cultivation. For Hansel, the maximum growth speed of microencapsulated cultivation had no obvious difference compared to the suspension cultivation. Moreover, after encapsulation, the production of glycerol was decreased for both Y02724 and Hansel compared to suspension cultivation. In conclusion, osmotic stress existed in the ACA microcapsules and affected the growth and metabolism of the cells.