Investigation of spore forming bacterial flooding for enhanced oil recovery in a North Sea chalk Reservoir

Little has been done to study microbial enhanced oil recovery (MEOR) in chalk reservoirs. The present study focuses on core flooding experiments designed to see microbial plugging and its effect on oil recovery. A pressure tapped core holder was used for this purpose. A spore forming bacteria Bacillus licheniformis 421 was used as it was shown to be a good candidate in a previous study.

Bacterial spore can penetrate deeper into the chalk rock, squeezing through the pore throats. Our results showed that injection of B. licheniformis 421 as a tertiary oil recovery method, in the residual oil saturation state, was able to produce additionally 1.0-2.3% original oil in place (OOIP) in homogeneous cores and 6.9-8.8% OOIP in heterogeneous cores.

In addition, the pressure gradient was much higher in the heterogeneous cores, which confirms that bacterial selective plugging plays an important role in higher oil production from the heterogeneous chalk rock. In all cases, an incubation period ('shut-in') after the bacterial and/or nutrient injection was needed to give sufficient time for the bacteria to grow inside the core and to produce more oil.

Our findings show potential application of bacteria as a plugging agent in heterogeneous chalk cores to improve oil production.