Improving microbial selective plugging technology through experimentally based modelling and simulation

Efficient utilization of existing oil resources has been and is an important research area for Norwegian continental shelf. However, despite constant development of new technology, between 25 and 50% of the oil is still in place after conventional recovery. Water injection or water/gas injection are common recovery methods. The introduction of water leads to growth and activity of bacteria that may cause problems like corrosion and low gas quality. On the other hand, bacterial growth in oil reservoirs may lead to enhanced oil recovery if we get the bacteria to work with us. The focus on microbial enhanced oil recovery (MEOR) has increased lately due to regulations requesting implementation of green and environmentally sound technology within the oil industry. Enhanced oil recovery by use of bacteria involves a range of complex processes that requires a multidisciplinary approach to research and modelling. Oil reservoirs consist of porous rock filled with oil. At start of production, oil is easily recovered due to reservoir pressure depletion. After some time however, there is a need for pressure support in form of water injection where water push remaining oil out of the reservoir. During prolonged water injection waterways are established, which results in by-passing of remaining oil. In the current project we focus on bacteria?s ability to form biofilm that plug waterways that are established during water injection. The waterways bypass oil and reduce the recovery efficiency. By plugging the waterways, the direction of injected water will turn towards oil-bearing parts of the formation. In the current project we have focused on gaining more knowledge on how biofilm grows and behaves in the pores they are set to plug. In order to get a good overview of all mechanisms involved we have studied the process under microscope where we can visually monitor the biofilm in a net of pores similar to that of reservoir rock. The knowledge we have attained from these experiments was used in the development of a mathematical model for pore scale that was further developed into a model for a larger scale such as a piece of reservoir rock (Darcy scale). This model can again be used to develop a model for simulation of how bioplugging may affect water flow and oil recovery in actual oil fields. The good thing about research on biofilm and their plug performance is that it generates so much general knowledge that also can be applied within other research topics. Since biofilm growth is a natural trait for bacteria one can imagine that they also may cause problems, and not only possible solutions.

Underveis i prosjektet har det vært god og fruktbar kommunikasjon på tvers av de vitenskapelige fagdisipliner involvert. Det har resultert i felles etablering av ny kunnskap og kompetanse gjennom studier av biofilmvekst i væskestrøm på poreskala nivå (eksperimentelle resultater, tolkning og publisering av disse), samt utvikling av matematiske modeller på pore og Darcy skala for simulering av biofilmvekst i porøse medier. Prosjektet hadde som formål å utvikle et simuleringsverktøy for en spesifikk biopluggteknologien for økt oljeutvinning (MEOR) for en industripartner, men har også med tilpasninger vært brukt til å simulere andre prosesser knyttet til biofilmvekst i porøse medier, for eksempel uspesifikk bioplugging av oljereservoar. Vi ser derfor også potensial for bruk av modellene til å simulere biofilmvekst i andre porøse medier enn oljereservoar, slik som for eksempel grunnvannsreservoar og geotermiske systemer.

Efficient recovery is essential for optimal exploitation of existing and new oilfields. In spite of technological advances, between 25 and 50% of the oil is left in reservoirs after conventional recovery. MEOR technologies are environmentally sound and cost efficient tertiary recovery methods for water injected oil reservoirs. Norway has a leading position in MEOR, with Statoil taking a first use position through the offshore development at Norne and later at the Statfjord field. MEOR is a complex process, where flow of multiple phases and their interaction with the rock surface are affected by bacterial growth and activity, metabolic components and structural changes. The project aims at studying MEOR mechanisms involved in adaptive bio-plugging of high permeable structures in heterogeneous reservoir formations. The processes involved in MEOR are encountered at various scales, but is initiated at pore scale. Our approach is to develop a pore scale and core model where the mathematical modelling is based on experimental data from both scales. The objective of this project is to develop of accurate mathematical models and numerical approaches for MEOR, capable to describe the relevant biological, physical and chemical processes occurring at various scales. Given the complexity of MEOR, this can only be gained by combining the practical insights from the laboratory experiments with a consistent treatment of the pore scale and transition to a heterogeneous porous system at Darcy scale, from both analytical and numerical point of view. This challenging task requires a tight interdisciplinary collaboration. Project members are Uni Research CIPR, University of Bergen, Technical University of Munich, University of Perpignan, Technical University of Eindhoven, UFZ Leipzig, FAU University and industrial partner GOE-IP.