The West Salym oil field is located in the West Siberian oil province (Russia). Its reservoir conditions are typical for the region: sandstone formation with temperatures as high as 83 °C, low crude oil viscosities of about 2 cP, and brine salinities in the range of 14,000-16,000 ppm. The field is waterflooded to maintain the reservoir pressure close to its initial level and to optimize oil recovery. Oil production from West Salym peaked in 2011 and since declined with increasing water cuts. The expected ultimate recovery factor due to waterflood, as reported in the field development plan, is between 35-40%. This recovery will be achieved through an evergreen waterflood optimization process consisting of infill/side-track drilling campaigns, pattern rebalancing, well workovers, etc. To increase the recovery factor, a tertiary oil recovery technique called Alkaline-Surfactant-Polymer (ASP) flooding was selected. Earlier studies indicated a potential of 15-20% incremental oil recovery due to ASP injection. Laboratory studies were started in 2008 with the surfactant/polymer screening and selection followed by core flooding experiments. In 2009, a successful single-well chemical tracer test was conducted to prove the efficiency of the developed ASP formulation at field conditions. In 2012 a final investment decision was taken to conduct a multi-well pilot to demonstrate oil recovery potential of the ASP flooding process and to collect sufficient information for decisions on subsequent commercial projects. Pilot operation was started in February 2016 with the start-up of the ASP mixing and injection plant. Active injection was completed in January 2018 and the end of production is expected in Q1 2018. The paper focuses on the pilot performance results, principal operational challenges and strategies to overcome them. The ASP injection resulted in the mobilization of a significant volume of oil in the confined 5-spot pattern. The water cut dropped from 98% prior to ASP injection to 88% due to oil mobilization by the ASP solution. The estimated incremental recovery is above 16% of the pilot STOIIP. Together with the mobilized oil a larger than predicted concentration of injected chemicals has been back-produced through the pilot producing wells. This has led to production issues, most notably failure of electric submersible pumps in the pilot producing wells due to carbonate scale and production of stable oil-water emulsions. Both issues required the use of methodologies and chemicals that were novel for West Salym field. The laboratory data and field observations collected during the pilot operation phase are presented to support our conclusions. Finally, actual vs. expected results of the ASP pilot and remaining uncertainties to further develop the chemical flooding technology are discussed.

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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. To successfully interpret the project outcome an extensive surveillance plan was put in place. A tracer program formed an important, stand-alone part of the plan. Tracers injection was designed and executed to evaluate the incremental oil production due to ASP injection by using A) change in volume swept between the pilot wells and B) change in oil saturations due to ASP flooding. This paper focusses on the practical aspects of the tracer program execution and how the tracer program results were used for the interpretation of the pilot. The West Salym reservoir is a sandstone formation with 83°C temperature, 2 cP crude oil viscosity, permeabilities ranging from 10 to 250 mD and porosity ranging from 18 to 22%. The field is operated as a mature waterflood, with oil production having peaked in 2011. To increase the recovery factor, a tertiary oil recovery technique (ASP) was selected. A confined five spot well pattern was chosen for conducting the ASP field trial. Due to low remaining oil saturation after the waterflood (executed also as a pre-flush for the ASP flood) the production watercut reverse due to the ASP injection changed only from 98% to 88-90%. Hence, it was important to evaluate the efficiency of ASP flooding using several independent approaches. In addition to field injection/production data, analytical and modelling techniques, the tracer data interpretation became a valuable source of information. Four tracer injection stages were conducted during West Salym ASP pilot. Passive and partitioning tracer injection/production data were analyzed using Shook's analytical method and supported by the reservoir modelling. Analytical analysis of field data was complicated by the production and injection upsets, as well as the changes in injected viscosities. Even though the requirement for steady state conditions were not fully met, the passive tracer recovery data provided an important input to the history matching of pilot dynamic model helping to determine the sweep increase due to injection of viscous chemical solutions. The partitioning tracer recovery data in the water post-flush were used to confirm the low residual oil saturation after ASP flooding.