Stimulation of indigenous microbes by optimizing the water cut in low permeability reservoirs for green and enhanced oil recovery

Kai Cui,Zhiyong Zhang,Shanshan Sun,Hailan Li,Pengcheng Fu,Zhongzhi Zhang

doi:10.1038/s41598-019-52330-2

Kai Cui, Zhiyong Zhang + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-52330-2

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Abstract

Low permeability oil reservoirs are a widespread petroleum reservoir type all over the world. Therefore, methods to recover these reservoirs efficiently are of importance to guarantee energy supply. Here we report our novel stimulation of indigenous microbes by optimizing the water cut in low permeability reservoirs for green and enhanced oil recovery. We aimed to investigate the characteristics of indigenous bacterial communities with changes in water cut in reservoirs by high-throughput sequencing technology, and reveal the mechanism and characteristics of the crude oil biotreatment under different crude oil-water ratio conditions and the optimum activation time of indigenous functional microbial groups in reservoirs. The indigenous microbial metabolism products were characterized by gas chromatography mass spectrometry. Results showed that Acinetobacter (47.1%) and Pseudomones (19.8%) were the main functional genus of crude oil degradation at the optimal activation time, and can reduce the viscosity of crude oil from 8.33 to 5.75 mPa·s. The dominant bacteria genus for oil recovery after activation of the production fluids was similar to those in the reservoirs with water cut of 60–80%. Furthermore seven mechanism pathways of enhancing oil recovery by the synergistic of functional microbial groups and their metabolites under different water cut conditions in low permeability reservoirs have been established.

Highlights

Low permeability oil reservoirs are a widespread petroleum reservoir type all over the world
These results showed that the indigenous microbes in the low permeability reservoirs survived mainly in the water phase and that the number of bacterial species in the oil phase was relatively small, similar to the results reported in the literature[24]
The relative abundance of Pseudomonas were 42.3%, 29.5%, 6.1%, and 27.2% in CQ.3–CQ.[6], whereas those of Acinetobacter were 5.8%, 5.6%, 48.4%, and 19.9% in CQ.3–CQ.[6], respectively. These results indicated that Pseudomonas and Acinetobacter were the main functional microbial genus for microbial enhanced oil recovery (MEOR) because they effectively utilized the crude oil as a carbon source to maintain their own life activities[26]; they can survive and reproduce on the oil-water interface[25]; and they can selectively degrade naphthenes and aromatic hydrocarbons at different water cut, and synchronous produce metabolites to reduce the viscosity of crude oil[20]

Summary

Introduction

Low permeability oil reservoirs are a widespread petroleum reservoir type all over the world. Different EOR technologies are employed worldwide including: thermal (steam injection, in-situ combustion, etc.), chemical (surfactants, polymers, solvents, alkali, etc.), microbiological, miscible gas (carbon dioxide) injection[10,11] These techniques have the potential to improve the mobility of crude oil, characteristics of the oilewater interface, swept volume of oil displacement agents in the reservoirs, microscopic oil displacement efficiency, and macroscopic sweep efficiency. Characteristics of microbial community structures in oil wells with changing in water cut in low permeability reservoirs and the mechanism of MEOR under different crude oil-water ratio conditions by functional bacteria for oil recovery are still largely unknown. How to optimize the combination of water flooding and microbial flooding with the changes of water cut in low permeability oil reservoirs is becoming a valuable research nowadays

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