Unlocking Optimal Recovery in Challenging Fluvio-Dominated Reservoirs: Achieving Success Through Polymer Injection
Authors: Navasumrit P. , Pancharoen M. , Worawutthichanyakul T. , Sinhabaedya P. , Ketmalee T. , Hanchaiphiboolkul S. , Boonnog C. , Boonphu T. , Srisuksomboon T. 
Published: April 2024

Polymer flooding stands as the forthcoming phase in the development strategy of the Sirikit Oil Field (S1) beyond mature waterflooding. In 2022, following successful initial projects, polymer injection was introduced in the Thap Raet area (TRT) — a region characterized by high structural complexity, restricted lateral continuity of fluvial-dominated reservoirs, thin sandstones layers, and multiple fluid contact regimes. Despite the challenging geology, the trial yielded positive results, opening the door for its widespread implementation across the entire field.

With insight gained from prior pilots, the preparation phase includes laboratory polymer screening, reservoir simulation, the design of the polymer injection unit, and well preparation. Comprehensive data acquisition has been conducted both prior to and during the injection period to capture the changes induced by the polymer through Fall-off Tests, Injection and Production loggings. To maintain a balanced voidage replacement ratio, thoroughly monitoring process has been established. Finally, the project's effectiveness is evaluated, considering various aspects of success criteria namely flow conformance improvement and incremental of ultimate recovery.

By constructing a representative sector model for the target blocks, polymer flood optimization was conducted, considering slug size, concentration, and injection duration. The simulation results confirmed the benefits of polymer injection, leading to the selection of an optimum scenario for development. A large-scale polymer pilot injection facility was designed for eight injectors with a wide range of injection capacity, allowing for future use in other locations. Polymer selection was based on validation tests conducted at an internal laboratory, assessing chemical performance with reservoir and fluid properties in the TRT area.

The integration of monitoring dashboard system enables accurate analysis of information during operation of all 5 patterns. Over a year, water cut reduction has been observed, but the degree varies based on the waterflood maturity of each block, reflecting the polymer flood response in the complex geological reservoir. Challenges arise from unexpected producer issues and viscosity sampling method, requiring close monitoring. Quarterly injection logging demonstrates improvements in the vertical injection profile. Integrating the evaluation results shows the ability to enhance oil recovery with significant oil gains above the waterflood baseline. No environmental impact on the surrounding community.

The achievement of favorable results in polymer injection within intricate Fluvio-dominated reservoirs can be credited to a profound understanding in geological aspects, detailed preparation, diligent monitoring, and thorough assessment involving multidisciplinary teams. This procedural approach and the insights gained will serve as an innovative groundwork for the successive complete implementation within the S1 or analogous fields.