Bhagyam Full Field Polymer Flood: Implementation and Initial Production Response

Abstract

Abstract Bhagyam is an onshore field in the Barmer basin, located in the state of Rajasthan in Western India. Fatehgarh Formation is the main producing unit, comprising of multi-storied fluvial sandstones. Reservoir quality is excellent with permeability in the range of 1 to 10 Darcy and porosity in the range of 25-30%. The crude is moderately viscous (15 – 500 cP) having a large variation with depth (15 cP – 50 cP from around 270 m TVDSS to 400 m TVDSS and then rising steeply to 500 cp at the OWC of 448m TVDSS). Lab studies on Bhagyam cores show that the reservoir is primarily oil wet in nature. Bhagyam Field was developed initially with edge water injection and with subsequent infill campaigns, prior to polymer flood development plan implementation, the Field was operating with 162 wells. Simple mobility ratio and fractional flow considerations indicate that improving the mobility ratio (water flood end-point mobility ratio is 30-100) in Bhagyam would substantially improve the sweep efficiency. Early EOR screening studies recommended chemical EOR (polymer and ASP flood) as the most suitable method for maximizing oil recovery. The lab studies further demonstrated good recovery potential for Polymer flood. Bhagyam's first Polymer flood field application started with testing in one injector which was later expanded to 8 wells. Extended polymer injection in these wells continued for four years. Observing a very encouraging field response, field scale polymer expansion plan was designed which included drilling of 28 new infill wells (17 P+ 11 I) and 24 producer-to-injector conversions. Modular skid-based polymer preparation units were installed to meet the injection requirements of the expansion plan. Infill producers were brought online in 2018 as per the plan but polymer injection was delayed due to various external factors. The production rate, however, was sustained without significant decline, aided by continuous polymer injection in initial 8 injectors, continuing water flood and good reservoir management practices. First polymer injection in field scale expansion started in Oct’20 and was quickly ramped up to the planned 80000 BPD in 4 months, supported by analyses of surveillance data, indicating very encouraging initial production response. Laboratory quality check program was designed to check quality of polymer during preparation and to ensure viscosity integrity till the well head. The paper discusses modular polymer preparation unit set-up and the additional installations designed to reduce pipeline vibrations during pumping of polymers., Experience gained while bringing online the polymer injection wells and the lab quality checks employed to ensure good polymer quality during preparation and pumping have also been discussed. The paper also discusses reservoir surveillance program adopted at the start of polymer injection like spinner survey, Pressure fall-off surveys and the stimulation activities that worked in improving the injectivity of polymer injectors. The paper further outlines the observations from the production response and the surveillance data collected to ensure good polymer flow in this multi-darcy reservoir.