Enhancing oil recovery of ultimate water-cut reservoirs with a novel methane-producing bacterial strain

Abstract

Most of the old oil fields in eastern China are now in the ultra-high water-cut development stage characte-rized by a rapid increase in water-cut, low oil recovery rate and inefficient water flooding. The existing technologies for enhancing oil recovery are no longer economically viable for crude oil extraction, necessitating the development of alternative techniques.This study focuses on a post-polymer-flooding oil reservoir in the Shengli Oil Field as an experimental area. The analysis of the reservoir microbial community structure and the study on the activation, reservoir adaptability and oil displacement performance of the novel methane-producing bacterial strain were conducted to explore its application potential in such reservoirs. The results showed a rich population of petroleum hydrocarbon degrading bacteria in the experimental area, which is conducive to the implementation of biogasification technology. Under simulated reservoir conditions, the novel methane-producing bacterial strain had good compatibility with the indigenous microorganism in the reservoir, achieving a gas production rate of 3.12 mmol/g oil after 90 days. This rate was 4.5 times higher than that from activating reservoir microorganisms alone, with methane accounting for 78% of the generated gas. Microbial community structure analysis revealed that the newly discoverd methane-producing bacterial strain comprised 35.9% of the community, playing a vital role in the significant increase in gas production rate. An adaptability study demonstrated that this bacterial strain exhibited exceptional gas production performance at reservoir temperatures below 65 ℃ and crude oil viscosities less than 1 356 mPa·s. Utilizing a laboratory-designed physical model, the impact of the bacterial strain on enhancing oil displacement performance was assessed. These results showed effective mobilization of residual oil at the model's top after bacterial strain injection, leading to a 5.4 percentage point increase in oil displacement efficiency under ultimate water-cut conditions. These findings support the proposal of using biogasification technology to enhance oil recovery in ultimate water-cut reservoirs.

Keywords

• methane gas
• biogasification
• novel methane-producing bacterial strain
• enhance oil recovery
• ultimate water-cut reservoir