Use of Tracers in the Alkaline-Surfactant-Polymer Pilot in West Salym
A.J. De Reus, V. Karpan, D.W. Van Batenburg and E. Mikhaylenko
Event name: IOR 2019 – 20th European Symposium on Improved Oil Recovery
Publication date: 08 April 2019
Info: Extended abstract, PDF ( 3.45Mb )
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An Alkaline-Surfactant-Polymer (ASP) pilot was executed in the West Salym oil field in the Russian West-Siberian oil province. An extensive surveillance plan was essential to the successful interpretation of the ASP pilot. A tracer program formed a significant part of the surveillance plan. This tracer program was designed and executed to A) understand the connectivity and sweep between the pilot wells and B) to determine the change in saturations due to ASP flooding. This paper focusses on the results of the tracer program. The West Salym reservoir is a sandstone formation with temperatures as high as 83 °C, low crude oil viscosities of about 2 cP and permeabilities ranging from 10 to 250 mD. The main oil bearing sand bodies are stacked deltaic sandstones interceded with shales. Individual sand bodies are relatively long, narrow and internally inhomogeneous with porosity ranging from 18 to 22%. The field is waterflooded, with oil production having peaked in 2011. To increase the recovery factor, a tertiary oil recovery technique (ASP) was selected. A confined five spot pattern was selected for the ASP pilot. Four tracer stages were conducted during the ASP pilot, where different tracers were injected in the injectors at the corners of the pilot pattern. Tracer results were analyzed using Shook’s method as well as reservoir modelling. The tracer stage during the pilot pre-flush showed a strong drift across the pilot area, resulting in a decision to shut in two producers near the pilot. During the subsequent (ASP) tracer stage, it was confirmed that the drift was reduced, and that conformance had increased due to the viscosity of injected fluids. Analytical tracer analysis was complicated by the production and injection upsets due to scaling, as well as the changes in injected viscosities: the requirement for steady state conditions were not met. Nonetheless, tracer data was important for history matching the ASP pilot dynamic model and determining the chemical sweep. The partitioning tracers in the water post-flush helped to confirm the low residual oil saturation after ASP.