Towards an Economically Viable (A)SP Flooding Project in West Salym

Abstract

Summary West Salym (WS) is a typical mature West Siberian oil field that has been developed since 2004 and waterflooded since 2005. Oil production peaked in 2012 and despite evergreen waterflood optimization activities the production from WS is declining. Expected ultimate recovery due to the waterflooding is 38% leaving significant oil in place as a target for tertiary oil recovery. The technique, called Alkaline-Surfactant-Polymer (ASP) flooding, was selected as the most suitable for WS reservoir conditions. To assess the technology potential a series of laboratory studies, a Single Well Chemical Tracer field test, and finally a multi-well ASP flooding pilot were executed. With incremental oil recovery of 17% the pilot project has demonstrated the technical success of ASP flooding. Currently, the project team is working on the economic viability of large-scale chemical flooding in WS to ensure further development of the project. This paper focuses on the workflow developed for scaling up the WS pilot results to a commercial-scale project and on the optimization of chemical flooding efficiency. Realistic representation of complex flow mechanisms and interaction of injected chemicals with the reservoir rock and fluids occurring during the (A)SP displacement is a technical challenge for the evaluation of the potential for a large scale commercial project. Dynamic reservoir modelling has been widely used for this task replacing the analytical techniques under the premise of delivering more reliable results. For accurate modelling of chemical flooding recovery mechanisms, the use of fine grid simulations, rather than coarse grids with upscaled physical properties, is recommended whenever feasible. Additionally, the chemical flooding optimization is an iterative process to find the most economic combination of chemical flood design (concentration of chemicals vs. slug sizes), surface/subsurface configuration and pace of project expansion. Such iterative forecasting combined with the need for fine grid dynamic models is usually associated with long run times. One key attribute of our approach is the use of modern dynamic modelling software that allows time-efficient modelling of the chemical flooding. A commercial simulator optimized to provide the best parallel performance on multicore platforms was used. The general formulation of the ASP flooding mathematical model valid for both black-oil and compositional descriptions, captures the major chemical flooding effects i.e. modification of relative permeability, interfacial tension, water viscosity, interaction and retention of injected chemicals, etc. The developed workflow has been successfully utilized to predict and optimize the performance of (A)SP flooding scenarios in tertiary mode for the West Salym oil field.