Bhagyam Field: Peripheral Waterflood to Full Field Polymer Flood. Subsurface, Reservoir Management & Field Development Learnings from 10-Year-Old Field Journey

Abstract

Abstract Bhagyam field is a moderately viscous onshore oilfield in the Barmer basin located in the western part of Rajasthan state in India. The main producing unit is Fatehgarh comprising of multi storied fluvial sandstones. Fatehgarh is an excellent reservoir with multi-Darcy permeability. The field was discovered in 2004 & has been in production since Jan-2012. A total of 200+ wells have been drilled in this field since the start of field development journey. The field has been on peripheral hot water flood since the start of production. A polymer flood pilot was done in the field in 2016 & based on the success of the pilot, full field polymer injection supported by peripheral water injection was commenced in Oct-2020. The paper captures the developmental journey of the field; challenges observed in the field during its production life, surprises encountered during waterflood phase & initial few years of polymer flooding phase and subsurface & modeling challenges encountered in the field. During the initial waterflooding phase, water breakthrough & the rise in water cut in the field was faster than expected. The then subsurface models were unable to capture early water breakthrough and fast water cut rise. The reservoir modeling philosophy in the field had to be revamped with updated understanding of the field to better capture field performance. Also, the field has a bio-degraded oil zone with relatively higher oil viscosity where a major part of the in-place volume is present. Commercial exploitation of the bio-degraded zone has posed its own challenges. The journey of polymer flood in the field has been a success story. The field has performed as expected but challenges in terms of injectivity, conformance, surface issues etc. have been observed. The paper discusses the learnings from the first few years of field production life when field performance deviated from expectations and the reasons for that deviation. The paper also summarizes how subsurface & reservoir management learnings from the initial field life were incorporated while planning polymer flooding in the field. The paper also discusses learnings from subsurface & operational challenges encountered during the initial few years of polymer injection in the field. The paper also summarizes how subsurface modelling has evolved in the field over time to better capture field performance. The understanding of reservoir characteristics, rock-fluid interaction & fluid movement in Bhagyam field has improved significantly in the last 10 years and this has led to improved reservoir management practices & better development planning of the field resulting in reserves addition & recovery factor improvement. The learnings from this field can be applied to similar reservoirs across the world.