Abstract

The Pirawarth Field, located in Austria, has been considered for polymer flooding. The reasons were the good permeabilities, medium viscosity of the oil (50 cP), low reservoir temperature (30 °C) and injection of low salinity water, resulting in low polymer concentration requirements.

Production from this field started in 1964. Until 2008, the recovery factor of the field reached 26 %. The reason for the low recovery factor is the unfavourable mobility ratio between the viscous oil and water.

In addition to conventional history matching, produced water chloride concentration data was implemented as matching parameter. The chloride concentration match revealed that the geological structure of the field was not well represented, although the water cut increase could be matched. This lead to delayed simulated breakthrough of the low salinity injected water. Improving the geological model enabled an improved match of the injected water breakthrough.

Laboratory experiments confirmed high efficiency of polymers in increasing water viscosity for the Pirawarth conditions. A core flood experiment was conducted and showed that adsorption is limited, the water relative permeability will be reduced by polymer injection and that the displacement with polymer after water flooding results in incremental recovery of more than 20 % of oil in place.

The core flood experiment was simulated and the parameters derived from the core flood experiment were used in the dynamic model of the field. The results of the simulation are very promising, indicating an increase in oil recovery in the pilot area of 5 %. It is planned to perform the pilot in 2010.

Introduction

The Pirawarth Field is located about 20 km northeast of Vienna in the Vienna Basin. First oil was produced in 1964. In 1977, water flooding was implemented. The recovery factor today reached 26 %. The Ultimate Recovery factor at abandonment of the field is expected to be 32 % applying the current production strategy.

In 2007, an integrated study was performed to identify opportunities to improve oil recovery from this field. Screening parameters for various enhanced oil recovery methods concluded that polymer injection is the most promising method to increase oil recovery after waterflooding at reasonable costs.

Geological setting/reservoir parameter

The dominant structural features in the Pirawarth area are the NE trending left lateral Steinberg and Vorstaffel Fault systems that controlled, as synsedimentary faults, the sediment input from the Upper Badenian on. The fault system is part of a large left lateral fault zone that forms the western termination of the Vienna Basin.

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