Abstract
The community diversities of two oil reservoirs with low permeability of 1.81 × 10−3 and 2.29 × 10−3 μm2 in Changqing, China, were investigated using a high throughput sequencing technique to analyze the influence of biostimulation with a nutrient activator on the bacterial communities. These two blocks differed significantly in salinity (average 17,500 vs 40,900 mg/L). A core simulation test was used to evaluate the effectiveness of indigenous microbial-enhanced oil recovery (MEOR). The results indicated that in the two high salinity oil reservoirs, one reservoir having relatively lower salinity level and a narrow salinity range had higher bacterial and phylogenetic diversity. The addition of the nutrient activator increased the diversity of the bacterial community structure and the diversity differences between the two blocks. The results of the core simulation test showed that the bacterial community in the reservoir with a salinity level of 17,500 mg/L did not show significant higher MEOR efficiency compared with the reservoir with 40,900 mg/L i.e. MEOR efficiency of 8.12% vs 6.56% (test p = 0.291 > 0.05). Therefore, salinity levels affected the bacterial diversities in the two low permeability oil blocks remarkably. But the influence of salinity for the MEOR recovery was slightly.
Highlights
Nutrient activator to maintain the growth and metabolism of the aerobic microbes[1]
The results indicated that the two blocks had distinct bacterial community structures
Based on the Shannon index analysis, Block Liu had a higher species diversity that was probably caused by the invasion of exogenous species in the injection water, which came from surface water and had low salinity (972 mg/L) and high microbial diversity
Summary
Nutrient activator to maintain the growth and metabolism of the aerobic microbes[1]. This method decreases the operational cost significantly and does not require microbial culture incubation above ground[2]. A number of studies have focused on the diversity of microbial communities, environmental factor (temperature, salinity, permeability, etc.), and influence of nutrient injection. The structure of the microbial community is influenced by oil reservoir geological conditions or external factors (nutrient injection, water flooding). The structure of microbial community changed remarkably with the increase of formation temperature[8,9]. The higher the temperature was, the less species in formation water would be Salinity is another influencing factor for microbial community structure. The bacterial community structure of a lower permeability reservoir with high salinity during the MEOR stimulation process have not been reported. The distribution of bacteria in two low-permeability oil blocks (Wangyao block and Liu block, Changqing, China) was characterized using high throughput sequencing techniques to determine the influence of salinity. We used a core simulation experiment to evaluate the performance of bacterial oil recovery and the influence of different permeability and salinity after stimulation
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