Located offshore southeastern India, the PY-1 field is a geological marvel, distinguished by its unusual primary reservoir – a Precambrian fractured granodiorite in the Porvo Novo Horst. This basement rock, exposed to weathering during the Late Jurassic to Late Cretaceous, underwent significant fracturing during subsequent Cenozoic tectonic episodes, creating a complex subsurface environment.

The reservoir, with its intriguing characteristics, exhibits an average bulk porosity of 7% (0.5% fracture porosity) and a permeability that ranges from 0.07-1548 mD (Fig. 1), averaging 6.5 mD. With a GIIP of 416 BCF and an EUR of 120 BCF (28.9% recovery factor), reservoir heterogeneity necessitates horizontal wells to enhance production.

Drilling through fractured granite is not without its challenges. Issues like gas kicks, lost circulation and formation damage are common. To mitigate these challenges, managed pressure drilling (MPD) has been implemented. This closed-loop circulation system, leveraging adjustable surface backpressure, enables quicker pressure adjustments, reducing mud losses in the 8½ in. horizontal sections using 9.4 ppg mud weight against a pore pressure of 9.2 ppg.

Disruptions at the onshore facilities contributed to early breakthrough and a decline in production. In 2018, two sidetracked wells were drilled: one targeted the upper basement using smaller 3½ in. tubing, resulting in rejuvenated gas rates to 3 MMCF/day, while the other tapped into the Eocene sands, adding another 2.5 MMCF/day to the overall daily field production (Fig. 2). This new plateau, however, proved short lived, lasting only a year before declining down to 1.2 MMCF/day and cumulative production reaching 33 BCF (Fig. 3).