From Pilot to Field-Wide Implementation: A Journey of Polymer Injection in the Largest Onshore Oilfield in Thailand
Authors: Pancharoen Monrawee , Worawutthichanyakul Thanawut , Laochamroonvorapongse Rapheephan , Trinavarat Pannapon , Sinhabaedya Prangtip , Kulprasoot Thipruethai , Rujipimolkit Chuthanart 
Published: September 2022

Enhanced Oil Recovery (EOR) is considered as the next stage of Sirikit Oil Field development strategy beyond waterflooding. The field contains light oil (40° API) in highly stratified sand-shale sequences with low net-to-gross ratios. Despite the challenging conditions for polymer injection including high reservoir temperature, low permeability, and high water cut, the large-scale polymer injection pilot has demonstrated a satisfactory result paving the way for field-wide execution in the field.

The large-scale polymer injection pilot has been carried out from September 2019 – August 2021 with 12 polymer injectors and 20 producers. Both technical and operational data were thoroughly analyzed during the pilot, including production and injection history, interwell tracer application, pressure transient analysis, and water distribution profile. Reservoir simulation model as well as analytical tools were utilized to evaluate pilot performance and estimate oil recovery gain from polymer injection. The successful strategies from the pilot were included in the design of the field-wide implementation. Finally, economic evaluation was performed for the field-wide development of polymer injection.

As evidenced by ILT and tracer studies, the large-scale polymer pilot injection demonstrated the ability to enhance oil recovery in pilot areas by improving vertical and area sweep efficiency. The additional recovery factor gain from the pilot was approximately 10% based on the STOIIP of the polymer-affected area. A significant water cut reduction of 20% was also observed within 6 months of injection. Additionally, there was no concern over back-produced polymer's effect on production facility and environmental impact to surrounding community.

Following the successful completion of the pilot, it is planned to expand the similar concept to a field-wide implementation in 2 additional areas in the same field. Injection flood pattern and scheme, operational philosophy, and key lesson learned from the pilot have been incorporated to minimize the uncertainty and risks. The oil gain expected from field-wide implementation was estimated using a reservoir simulation model calibrated with actual field data. The economic impact of increasing oil recovery with different pore volume injections was evaluated, and a three-year injection was proposed to get the best economic outcome. The robust project economic justification results in a field-wide execution scheduled for late 2022.

The field trial of polymer injection revealed the potential to significantly improve oil recovery in the Sirikit oilfield which comprises several sub-areas with different reservoir properties. This field-wide implementation is the first field-level polymer injection in Thailand and is a steppingstone to the sequential studies of EOR implementation in the field based on development phase and complexity of reservoir properties in each area.