Innovative Well Intervention Techniques to Sustain Production in Mature Offshore Fields

摘要

Abstract Cairn India is an operator for two mature offshore fields in India – Ravva and CB/OS-2. Due to high offshore rig cost combined with cost recovery risks, innovative well intervention techniques are implemented in both the fields to sustain production & enhance injection. This paper summarizes some of the successful well intervention cases over the past few years and how it changed the approach towards meeting production targets. Case 1: Slickline conveyed straddle gas lift technique to activate and produce from a previously shut-in well. Case 2: Wireline conveyed robotic tools to retrieve downhole screen and restore well injection. Case 3: Modular CT units and advanced downhole tools for well stimulation improving production by multiple folds. Case 4: Specific chemical system to successfully complete a vessel based stimulation campaign in water injectors; this led to an overall two-fold increase in the field injection rates. Case 5: Advanced downhole camera to identify wellbore held-up reasons during regular interventions and how it has led to several important decisions saving time and cost. The operator always looked at challenging problems as opportunities for innovative solutions. The above interventions were focused on well revival using cost effective and innovative well intervention techniques avoiding rig based workover and achieving the objective in all the above cases. A synopsis on the recently completed cases and future inventive solutions is covered in last section of the paper. Field Introduction Ravva is located 10 kms off the shore of Godavari Delta on the east coast of India. The anticline structural reservoirs are multi-Darcy sands of Middle Miocene age. The field oil is light with an API gravity of 35o and GOR of the range 470 – 520 scf/bbl. The field was developed through 8 unmanned platforms with production commencing in 1993. Water injection was introduced in 1997 for reservoir pressure management and is the supporting drive mechanism. Water-oil displacement characteristics are excellent due low oil viscosity, high permeability, low residual oil saturation and good areal pressure communication. Almost all wells are producing with Gas injection for artificial lift. After a sustained plateau production period of 50,000 bopd, the field currently is on decline with increasing water cut (average water-cut ranging from 60% - 90%).