Abstract

This paper discusses the design and results of a polymer test in a field containing heavy oil. The field is located in the south of Oman and contains significant in place volumes of viscous oil (700cp) in sub Darcy reservoir. Due to unfavorable oil-water mobility ratio, the ongoing water injection will still leave significant volumes of stranded oil post water injection.

A "Paradigm Shift" from energy intensive thermal processes, high viscous polymer flood is currently being evaluated to target and recover stranded high viscosity oil. If successful not only would the oil recovery from the field be significantly increased but a reproducible process would be available to target other high viscosity oil reservoirs in Oman.

A single well injection test was conducted in 2014 representing the first foray into high viscous polymer flooding for the field. The driver for conducting the test was to de-risk polymer injection as a pre-courser to a full field expansion. To that end the following KPI's were identified.

  • Matrix injection – can economical rates at design pressures be achieved

  • Low salinity – clay swelling and subsequent loss of injectivity

  • Alternate higher molecular weight polymer's – can injectivity be maintained or is polymer plugging

  • Conformance – Applicability to full field / is conformance control required

  • Fracture pressure – Defining injection envelope for full filed expansion

The test comprised of a converted horizontal producer that was retrofitted with Disturbed Temperature and Acoustics (DTS & DAS) fiber optics. Modular polymer facilities capable of injecting high viscous polymer slugs at high rates were utilized; additionally a modular low salinity process was also used to drop the injected water and polymer salinity to 500ppm TDS.

The following have been identified as key learning's from the test:

  • A lack of conformance was identified through DTS and DAS evaluation during initial water injection, prior to the injection of any polymer

  • A loss of injectivity was also observed over a period of the test. This affected subsequent polymer and water injection periods.

  • The behavior of in-situ polymer highlighted possible unexpected phenomena, particularly the effect on water injection post polymer injection.

  • Low salinity, 500ppm TDS, water was injected with and without polymer with no adverse affect on injectivity.

  • Additionally, the higher molecular weight polymer also was successfully injected.

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