Petroleum is becoming a limited commodity due to increasing global demands attributed to industrialization and the population boom. Because the conventional methods of oil recovery have exhaustively reached an economic limit, developing novel technological approaches in oil extraction is therefore a priority concern. One proposed strategy is the microbial enhanced oil recovery (MEOR), which is purported as an effective method to improve oil recovery from low-permeability reservoirs in China. Although this method is considered minimally invasive, low-cost, and operationally simple, it has not been widely applied in the oil industry. Here, we discuss the technical details of MEOR in laboratory settings and field tests. The current challenges in employing MEOR from lab settings to industrial pilot scale-ups are systematically presented, here, including its economic implications. Central to this review is the synopsis of our findings on the applicability of MEOR and micro-foam method in the northwest district of China (Shaanxi province), along with the successful cases of these applications in other countries. This article also focused on a newly developed flooding technology, the so-called genetically engineered microbial enhanced oil recovery (GEMEOR). In addition, we included our proposed operational designs on GEMEOR and its technological potentials on an industrial scale. This review therefore demonstrates the creditability of MEOR, and may provide more guidance for the application of GEMEOR in Chinese oilfields.

The combination of strains of different species and genera may enhance the effects of single bacteria, surpass the tolerance upper limit, and optimize the viscosity reduction and degradation. In this study, six strains were isolated in low permeability layers of the Ordos Basin and were combined to verify the effect of the consortium strains. The selected single strains have good emulsifying and viscosity-reducing effects, but their degradation components are different. SC4561 (Bacillus cereus), SC4551 (Bacillus sp.), and H-1 (Brevibacillus sp.) form consortium A, and SC4534 (2) (Bacillus sp.), SC4542 (Bacillus licheniformis), and A-3 (Bacillus licheniformis) form consortium B. The performance of the mixed strains was evaluated by the analysis of change in emulsification rate, crude oil composition, viscosity, and the tolerance (temperature, salinity, and pH) through GC-MS, rotational rheometer, and other methods. The results showed that the temperature tolerance of the consortium strains was improved by 5-7°C. Consortium B had higher emulsibility ( was higher than 40% in average) and viscosity degradation (above 35%), and the crude oil in consortium B has almost no wall adhesion. The components of crude oil that consortia use were still diverse, including both long- and short-chain hydrocarbons. However, the proportion of long-chain n-alkanes is further reduced compared with that of single bacteria, and the highest ratio was reduced by 23.81% (B-ALL). At the same time, they also had effects on aromatic hydrocarbons with complex structures (phenanthrene and phenanthrene). This research confirms the enhanced effect of consortium bacteria on single bacteria, facilitating the implementation of microbial enhanced oil recovery technology in the future.

Microbialenhanced oil recovery has gained more attention in recent years due to its low cost and eco-friendliness. However, studies on the application of this technique in the low-permeability reservoirs are few. In this study, eight strains from the Ordos Basin low-permeability reservoir that produce biosurfactant and reduce viscosity were identified. Strains could produce biosurfactants (lipopeptide and glycolipids) to emulsify the oil and had good tolerance on temperature (25C-50C), salinity (1g/L-50g/L), and pH (5-10). After the actions of A-3, SC4534(2), SC4561, and JSC4535, the content of long-chain n-alkanes were decreased by 51.2, 28.3, 35.2, and 28.9, respectively. The naphthalene in aromatic hydrocarbons was also effectively degraded by the strains that were screened, and the degradation rate was higher than 84. Additionally, all strains were able to reduce oil viscosity, which was reduced by 27-51 (in seven days). 16S rRNA gene sequencing analysis indicated that seven strains belong to the genus Bacillus and one belongs to the genus Rhodospirillaceae. The results revealed that the existence of high-efficiency strains that can significantly improve the properties of crude oil in low-permeability oil fields though biodegradation and use of biosurfactants, which is of great significance for the application of MEOR in low-permeability oil fields.

Petroleum microorganisms play a crucial role in the application of microbial-enhanced oil recovery, and the community structures of petroleum microorganisms have been widely studied. Due to variations in reservoir geological conditions, reservoir microbial communities exhibit unique characteristics. However, previous studies have primarily focused on microbial community changes within a single well, a single block, and before and after water flooding, and thus, cross-horizon and cross-regional comparative studies of in situ microbial communities are lacking. In this study, the 16S rRNA full-length sequencing method was adopted to study bacterial communities in crude oil samples taken from two wells at the same depths (depths of 2425 m and 2412 m) but approximately 20 km apart in the Hujianshan oilfield, located in the Ordos Basin. At the same time, the results were combined with another layer of research data from another article (from a depth of 2140 m). The aim was to compare the differences in the microbial community structures between the oil wells on a horizontal scale and a vertical scale. The results revealed that there were minimal differences in the microbial community structures that were influenced by the horizontal distances within a small range (300 m) had significant impacts on the communities, and this was mainly controlled by temperature. The greater the depth, the higher formation temperature, leading to an increase in thermophilic and anaerobic bacteria within a community.

The production of value-added bioproducts from renewable carbon sources has gained increasing attention in recent years. The aim of this study was to develop economical approaches for the production of prebiotic XOS with defined degree of polymerization (DP) by Bacillus subtilis MR42 from corn stalks. The MR42 strain has been genetically modified to delete the xynC gene, which enables it to convert xylan into specific XOS without generating xylose as a byproduct. Under optimal conditions, a high yield of XOS (703.4 mg/g xylan) was obtained. The purified XOS were further characterized using various techniques including TLC, HPLC, ESI-MS and 1HNMR spectroscopy. The analysis revealed that the XOS primarily consisted of xylotriose (257 ± 0.14 mg/g XOS), xylotetraose (267 ± 0.24 mg/g XOS) and xylopentaose (289 ± 0.29 mg/g XOS), accounting for 81.3% of the total XOS. The prebiotic effect of XOS was evaluated by examining its impact on the growth of Lactobacillus, the production of short-chain fatty acids, and its antioxidant activity. B. subtilis MR42 showed a promising ability to produce XOS of DP 3–5, without the generation of xylose.