Cairn India operated Ravva Field is located offshore Krishna-Godavari (KG) Basin on the east coast of India. The field was discovered in 1987 and was brought into production in 1993 from the Middle Miocene sandstones. Oil production rate reached its plateau of ~50,000 bopd by 1999. The field produced at the plateau rate for ~ 9 years before starting to decline by the end of 2007.
Two infill drilling campaigns were planned and executed in 2007 and 2011 to arrest the production decline and add incremental reserves to the field. New infill wells increased production for a short while but failed to arrest the prevailing declining trend. By the end of 2013, Ravva oil production dropped to ~21,000 bopd and was declining by 35–40% per year. Arresting the production decline by finding additional reserves in a mature waterflooded field which had already achieved ~49% oil recovery was a challenge with significant risks. Planning for additional infill drilling targeting areas of undrained oil required an integrated approach with adoption of advanced technologies to minimize risks.
A 4-D monitor seismic survey was acquired in 2010 over the Ravva field and co-processed with a vintage baseline survey to identify areas of undrained oil. Separate processing of the 2010 high density 3-D survey provided improved seismic imaging of the subsurface architecture. A high resolution 3-D model was created by using sequence stratigraphic concepts, fault seal analysis studies, detailed property modeling through integration of seismic attributes, log and core data. An integrated subsurface study was initiated in 2011 to identify infill well opportunities in the field. A full cycle of integrated reservoir modeling from seismic to simulation was carried out using advanced technologies and workflows.
The integrated study resulted in the identification of several infill opportunities as well as near field exploration and appraisal targets. The Ravva Phase-5 drilling campaign executed in 2014-15 comprising 8 infill, 1 water injector, and 2 exploration/appraisal wells was the most extensive infill campaign in the field's history. Well results from the drilling campaign have been very encouraging. The ten producers drilled in the campaign together added ~18,000 bopd to the field production and they are estimated to improve the field oil recovery by ~3%. By March 2015, when all new wells were brought online, Ravva field production had once again reached 28,000 bopd. The success in near field exploration and appraisal has extended the producing field boundary and has identified upsides that could support future drilling campaigns.
The Ravva Phase-5 drilling campaign has showcased the first successful application of a 4-D OBC seismic project in India. New technologies such as 4-D seismic combined with integrated subsurface reservoir modeling can demonstrably arrest production decline in comparable mature oil fields and drive recovery factors closer to the technical limit.