In recent years, exploration in northeast India has focused mainly in the area south of the Naga fault. This area is tectonically active with complex folding and faulting. Target formations are in excess of 3,000m through these complex structures. ONGC has drilled several wells in the Tripura region of northeast India. Although results were encouraging, the main challenges faced during drilling were various well control and instability events: kicks, tight hole, stuck pipe, lost in hole, etc. The causes of this instability were difficult to isolate. Experience from past wells also indicated the existence of overpressure in the Middle Bhuban Formation, which could not be accurately predicted by surface seismic data. Hence, drilling through these highly stressed and overpressured formations led to excessive NPT and cost. In addition, severe hole enlargement and rugosity through eventual reservoir sections resulted in poor logging conditions and uncertain reservoir evaluation. As a result, access and interpretation of the reservoirs, to prove and produce reserves, is a major challenge in this region. In this paper, two case studies are presented to show how a geomechanics-based approach has significantly improved drilling rates by reducing the drilling-related problems. New wells were drilled within 40% of the planned number of days. Better hole conditions not only improved drilling performance but also led to huge improvements in reservoir evaluation and the identification of unloading mechanisms, probably caused by uplift due to thrusting, in the Middle Bhuban Formation. Integrated study provided valuable information about overpressure and stresses acting in this field/structure for future drilling.

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