Jasmine: The challenges of delivering infill wells in a variably depleted HPHT field

Drilling infill wells into a heavily depleted reservoir poses several challenges which can lead to increased time, cost and risk. Data acquisition, including gathering formation pressure data, can be severely compromised, complicating real-time decisions and pore pressure interpretation. Fracture gradients, usually constrained by data acquired outside the reservoir, need to be estimated using a different approach through a depleted reservoir. The Jasmine HPHT Field in the UK Central North Sea can be used to illustrate some of these challenges and describe some practical solutions. A qualitative approach to estimating the level of reservoir depletion from formation gas measurements has been developed for the Jasmine Field, comparing pre-depletion gas trends against those obtained during the infill drilling campaign. The methods described here to estimate depleted fracture gradients using modelled and observed stress paths coupled to the pore pressure reduction were found to fit with well observations and have helped inform operational decisions to manage severe lost circulation events. A strategy to acquire data in memory while drilling has proved successful and has allowed lost circulation events to be managed safely. Managed Pressure Drilling has opened up narrow drilling windows and has reduced the number of hole sizes and liners required to drill these infill wells. Thematic collection: This article is part of the Geopressure collection available at: https://www.lyellcollection.org/topic/collections/geopressure