An Integrated MEOR Project; Workflow to Develop a Pilot in a German Field

Abstract

Abstract The workflow and the results of the work packages of a Microbial Enhanced Oil Recovery (MEOR) project aiming at a pilot are introduced and discussed. An enrichment culture consisting of a community of various microbial species derived from one of the Wintershallfields shows good growth and EOR characteristics upon nutrient stimulation tailored for the given reservoir characteristics, including high salinity (160000ppm). The emulsification indices as well as measured interfacial tensions (IFTs) between dead oil and the microbial culture supernatant collected during the exponential and stationary growth phases indicate potential beneficial impacts on capillary forces. Imbibition experiments with Bentheim sandstones support the measurements. The rheology of cell-free medium after growth shows pseudoplastic behavior resulting in viscosities of up to 3-6mPa•s at representative shear rates. An important EOR effect was gas (CO2) generated during growth, which resulted in a calculated reduction of 3-4mPa•s in oil viscosity. The effect of pressure (reservoir pressure is 30bar) on the metabolite generation is being investigated with growing cells in high-pressure bio-reactors. Model systems including micromodels, sandpacks and corefloods were used under sterile and anaerobic conditions to monitor the oil displacing effects of the nutrient-stimulated communities. Experiments using polydimethylsiloxane (PDMS) micromodels consisting of channels with different pore sizes indicated an improvement of the sweep efficiency potentially due to selective plugging. A sandpack system was designed to test the dynamic performance of the bacteria and proposed nutrient formulations. The flooding tests performed under reservoir temperature showed incremental oil of up to 18% of OOIP after three successive medium treatments. The oil recovery performance of the proposed nutrient formulations is also being tested with coreflooding experiments at reservoir pressure and temperature. Numerical simulation work packages focused on modeling all MEOR components as tracer in oil and water phases and implement growth/decay of bacterial cells by Monod equation. The implementation of this concept into the commercial reservoir simulator STARS/CMG using its reaction kinetics option is ongoing. Polymer and surfactant effects in water phase and gas generation effect on oil viscosity are modeled using standard approaches. The parameters are calibrated with batch as well as dynamic growth experiments. The implementation was validated by comparison to data obtained from sandpack and coreflood experiments. Results of both experimental and numerical work packages indicated additional oil recovery due to selective plugging, emulsification, CO2 generation and beneficial viscosity changes of water and oil phases.