Bockstedt, a mature oilfield in Northern Germany, was discovered in 1954 and put on-stream in the same year. The waterflooding of this high permeability Valanginian sandstone reservoir, with moderately viscous oil and highly saline brine was started in 1959 and continues to date, albeit at a high watercut. A compartment within this field was selected for a pilot test of the biopolymer Schizophyllan; a polysaccharide, with considerable viscosifying efficiency and high salinity and temperature stability.
As the biopolymer flood progresses, surveillance and monitoring techniques that estimate in-situ polymer properties and help to understand the influence of the polymer on reservoir performance are applied. Operational procedures have also been developed and tested to ensure a manageable restart of operations in the event of planned and unplanned well shut-ins. Production logging test runs in the injection well during the water injection phase showed a homogeneous injection profile over the reservoir interval. Well logs from new wells drilled within the pilot area provide additional insight with regards to the saturation distribution. Passive and partitioning tracers have been injected and are regularly being sampled and analysed.
After a successful polymer injectivity field test was conducted in mid-December 2012 for Schizophyllan, continuous polymer injection commenced in early January 2013. High-resolution data available from permanent downhole gauges show an initial increase and subsequent stabilization of bottom-hole pressure at a higher value in the injection well after the start polymer injection. A modified Hall plot used to assess the polymer injectivity does not show any significant reduction in injectivity. An estimation of the reservoir properties during the water injection phase and subsequently the in-situ effective polymer viscosity during the polymer injection phase using several falloff tests confirms that, the polymer is not shear degraded in the reservoir and offers insight as to the position of the polymer front in the reservoir. The work was accompanied by numerical simulation to better understand the in-situ rheological properties of the polymer.
This paper discusses the challenges, experiences and early results from the operational aspects of an on-going polymer flood pilot in a mature oilfield after an early technical evaluation.