Results of Alkaline-Surfactant-Polymer Flooding Pilot at West Salym Field

Abstract

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.

Oil Recovery Performance by Surfactant Flooding: A Perspective on Multiscale Evaluation Methods

“…Among those techniques is the temperature log, which could be utilized to avoid the risk of injecting out of the zone. Saturation logs are also useful for monitoring the vertical saturation distribution and propagation of the oil bank …”

“…Saturation logs are also useful for monitoring the vertical saturation distribution and propagation of the oil bank. 201…”

Alkali Polymer Flooding of a Romanian Field Containing Viscous Reactive Oil

“…The positive effects of alkali on polymer solution viscosity development, adsorption, and injectivity, and the long-term stability of polymers in alkali solutions were explored by Nurmi et al [ 16 ], indicating additional economic benefits of AP flooding over polymer flooding. While various chemical enhanced oil recovery (EOR) projects have been successfully field-tested and implemented for light oils (e.g., Guo et al [ 17 ], Pandey et al [ 18 ], and Volokitin et al [ 19 ]), heavy oils require additional chemicals to polymers for increased production over waterflooding. Alkali and surfactant injection induces emulsion formation and channel blockage in waterflooded cores and micromodels (e.g., Bryan et al [ 20 ], Dong et al [ 21 ], Xie et al [ 22 ], and Xiao et al [ 23 ]).…”

Screening of Chemicals to Enhance Oil Recovery in a Mature Sandstone Oilfield in Kazakhstan: Overcoming Challenges of High Residual Oil

“…Guo et al [21] also indicated that even in cases of low TAN, a synergistic effect between the injected synthetic surfactants and the in situ surfactants leads to an ultra-low interfacial tension [22]. Additionally, injecting alkali into reservoirs with low TAN is beneficial as alkali helps reduce surfactant adsorption [23]. The adsorption reduction happens because of the increasing pH level of the system.…”

“…A higher pH increases the negative charge of the reservoir rock and surfactant molecules, so more electrical repulsion between surfactant molecule and reservoir rock occurs [24,25]. Since alkali is less costly than surfactant, using it even with low TAN crude oil can be economically beneficial as it can significantly lower the surfactant consumption [5,23].…”