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During the development of low permeability oil reservoirs in Changqing oilfield, the nonuniformity of injection profile is a commonly seen problem. Conventional profile control methods face the difficulty caused by hard injection and poor reservoir adaptability. Polymer microspheres (PMs) are considered to have good profile control capabilities due to their properties such as hydration swelling and plugging. Therefore, it is proposed to use PMs profile control method to improve the oil recovery in low permeability reservoirs. There are two key factors for the success of PMs profile control, which are matching relationship and plugging properties. In this paper, the average pore throat diameter of the pilot test area was calculated, and the hydration swelling properties were studied by measuring the diameter of PMs. The plugging properties of PMs were studied by displacement experiment. Based on the experimental research, in 2016, 4 well groups in Changqing oilfield were selected for PMs profile control. Calculation results showed that average pore throat diameter of the study area was 2.28μm. The diameter of 800 nm named PCE been selected for PMs profile control. The hydration swelling experiment results showed that PCE initial average diameter was 784nm. After 13 days of hydration swelling, PCE average diameter was 2798 nm and increased by 2.57 times. The results of PCE displacement experiment showed that resistance factor, blocking rate and retention rate was 3.5, 71.42% and 96.22%, respectively. The performance of the PCE application in oilfield showed that 11 production wells were effective after PCE injection, and the success rate of profile control was 47.8%. The average validity period was 150 days. And a total of 1365.5t of oil had been increased during the validity period. For the injection wells, the average injection pressure and the thickness of water absorbing layers increased by 1.415MPa and 3.28m respectively.

Microbial mineralization (corrosion, decomposition, and weathering) has been investigated for its role in the extraction and recovery of metals from ores. Here we report our application of biomineralization for the microbial enhanced oil recovery in low-permeability oil reservoirs. It aimed to reveal the etching mechanism of the four Fe(III)-reducing microbial strains under anaerobic growth conditions on Ca-montmorillonite. The mineralogical characterization of Ca-montmorillonite was performed by Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, and energy-dispersive spectrometry. Results showed that the microbial strains could efficiently reduce Fe(III) at an optimal rate of 71%, alter the crystal lattice structure of the lamella to promote interlayer cation exchange, and efficiently inhibit Ca-montmorillonite swelling at a rate of 48.9%. Microbial mineralization is ubiquitous in the natural environment. Microbes in low-permeability reservoirs are able to facilitate alteration of the structure and phase of the Fe-poor minerals by reducing Fe(III) and inhibiting clay swelling, which is still poorly studied. This study aimed to reveal the interaction mechanism between Fe(III)-reducing bacterial strains and Ca-montmorillonite under anaerobic conditions and to investigate the extent and rates of Fe(III) reduction and phase changes with their activities. Application of Fe(III)-reducing bacteria will provide a new way to inhibit clay swelling, to elevate reservoir permeability, and to reduce pore throat resistance after water flooding for enhanced oil recovery in low-permeability reservoirs.

Wettability modification is one of the main mechanisms to increase oil recovery from low-permeability oil reservoirs. Nanofluids composed of nanoparticles can be used as modifiers to alter wettability from oil-wet to water-wet condition thus to promote hydrocarbon recovery. Biosurfactants, which are candidates to replace synthetic surfactants for industrial applications, have the potential to prepare nanofluids. In this study, nanofluids prepared by dispersing SiO2 nanoparticles in rhamnolipid solution (hereby named bionanofluids) were considered potential wettability modifiers to apply to petroleum recovery from low-permeability sandstone reservoirs. Analyses via visual observation, optical absorbance measurement, ζ-potential determination, and particle size measurements demonstrated that the bionanofluids with 25 ppm rhamnolipids maintained an optimal stability. The effect of bionanofluids on wettability alteration was investigated through contact angle measurement and imbibition test. The results showed that bionanofluids could alter the wettability of oil-wet sandstone to strongly water-wet. The best performance was achieved with a nanoparticle concentration of 1000 ppm. Additionally, a micromodel test using rhamnolipid solution and bionanofluid was carried out to evaluate the synergistic effects of SiO2 nanoparticles and rhamnolipid on displacing oil. Bionanofluid injection following biosurfactant flooding was shown to improve oil recovery, yielding an additional 5% production. These results reveal that the bionanofluid prepared with SiO2 and rhamnolipids not only remained stable but also provided a potential way for enhanced oil recovery.