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.

This paper provides an update on a microbial enhanced oil recovery (MEOR) project conducted by Wintershall and BASF. Overall nutrient development and planning of a single well field trial (huff'n'puff, HnP) including risk management are described. A nutrient solution is tailored to stimulate growth and metabolite production of a reservoir community of various indigenous microbial species in a Wintershall operated oil field with challenging reservoir characteristics, including high salinity (160,000 ppm). Up-scaled imbibition experiments performed with sandstone cores using MEOR-oil systems are compared with injection brine-oil systems and assessed for the implications on incremental oil. The results of sandpack and coreflood experiments performed with optimized nutrient solutions are discussed regarding incremental oil recovery and responsible EOR mechanisms. A MEOR modelling concept developed using STARS/CMG is used to estimate additional oil production under various feeding strategies after the calibration of the EOR mechanisms assigned.As the laboratory and numerical works have indicated the feasibility of the MEOR field application, emphasis has been put on risk issues ranked in the register of the project. The key risk is potential souring of the reservoir due to the activation of the sulphate reducing bacteria (SRB) growing on the metabolites generated by the MEOR target community. Conventional mitigation measures have been tested in short and long-term experiments. An innovative solution had been developed to assure H 2 S free application without any consequences to the reservoir and to the MEOR application.A single well pilot application is planned in a pre-selected well of the Wintershall field studied with two main objectives: (1) proof of the concept of risk mitigation and (2) stimulation of growth and metabolite production. Identification of operational issues as well as data gathering to improve the forecasting methods towards full-field predictions are secondary objectives. A monitoring plan has been initiated to establish a baseline in terms of microbiological and petro-dynamic parameters. Temperature and volumetric distributions have been predicted based on the results of an injectivity test performed in the well. The data is used to design the HnP operation and the surface setup for the injection rate of 100 m 3 /day nutrient solution under well-defined conditions.

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MEOR (microbial enhanced oil recovery) is known as low-cost and easy to apply EOR technology. It uses the fact that natural occuring microrganisms in the oil reservoir can be stimulated to create effects that may result in mobilizing oil and sweeping it to the production well. During bacterial stimulation, there is always the risk that the growth of sulfate-reducing microorganisms, specifically bacteria (SRB), which are present in many oil reservoirs, is also triggered and toxic and highly corrosive H2S could be produced. The paper reports an investigation of microbiological H2S production and its mitigation. The project is jointly run by Wintershall and BASF in the context of a MEOR project in a German oil field. Different SRB inhibitors (one of them being nitrate) have been tested. The inhibitors have different modes of action regarding H2S inhibition, bacteriocidal activity and also show other side reactions. In growth experiments with original reservoir water, it was observed that some inhibitors can prevent H2S formation. It was concluded that very high nitrate concentrations (100 – 500 mM) are necessary for a long-term suppression of H2S up to 41 days. Furthermore, in cultures with nitrate, iron and calcite precipitations were observed as the result of chemical reactions induced by bacterial activity. Reactive flow simulations were performed using Toughreact to predict the impact of those precipitations on the permeability of the reservoir. In contrast to these findings, alternative inhibitors could successfully mitigate H2S production in long-term experiments without any complications. Based on this data and predictions, the use of an alternative SRB inhibitor is preferred over nitrate in the upcoming field pilot.

The Vega subsea field in Norway has been producing successfully using a continuous Mono Ethylene Glycol (MEG) injection, topped up with corrosion inhibition means. A topside reclamation process allows re-use of MEG, however, limits the possibilities to produce saline water. In order to manage wells producing saline formation water and to increase ultimate recovery, a new flow assurance and integrity philosophy without continuous MEG injection is considered. This paper describes the options on hydrate as well as integrity management and the modifications both on the subsea and topside facilities required to enable an operational philosophy change. This change of the operational philosophy appears feasible, using either timely depressurization or Low Dosage Hydrate Inhibitors (LDHI) as well as a film building corrosion inhibitor in the system.