Design and Execution of an MEOR Huff and Puff Pilot in a Wintershall Field

摘要

Wintershall is conducting a technology project for development and field application of MEOR (Microbiologically Enhanced Oil Recovery) in collaboration with BASF. The successful results of the laboratory phase led to a first small confined pilot Huff'n’ Puff (HnP) in a Wintershall mature oil field to prove that the laboratory-developed concept works in the field under reservoir conditions. A suitable well for the MEOR operation was selected in the studied field based on selection criteria. The selected well is a former producer approximately 900 m deep. After a USIT run it was decided to recomplete it. Prior to MEOR HnP pilot, an injectivity test was performed to allow for re-assessment of the current petrophysical and geological properties around the well. In order to establish the baseline for the pilot evaluation, a comprehensive monitoring program consisting of microbiological, chemical and petrophysical surveys commenced just after the well recompletion. The surface set-up designed for follow-up MEOR field operations was installed in the field. The mixing of the MEOR solution with the injection water was regulated automatically by measuring the injection rate. The injection took four days, followed by an incubation period of five weeks. During the nutrient injection, the injectivity was significantly lower than the one obtained from a previous injectivity test. As a result, the total volume of injected nutrient was lower than initially planned. Nevertheless, the volume was sufficient to achieve the pilot objectives. The injection was carried out under matrix conditions by keeping the pressure below the fracture pressure. The injected fluid temperature was somewhat lower than planned, but according to downhole measurements, still high enough for microbial growth. It was observed that there was an oxygen ingress into the system through the injection pump, however no detrimental effect was seen on microbial activity. After the shut in period, a comparable volume of the injection fluid was produced back. The tracer concentration in the back produced fluid was used to calibrate the chemical and microbiological effects of MEOR.