Abstract

An extended-reach, S-shaped appraisal/development well drilled from a platform to prove up and drain a field extension in a Rotliegendes sandstone reservoir has been hydraulically fractured with a proppant-based stimulation treatment. The hydraulic fracture was a means to optimise the production rate and involved an injectivity test followed by a main treatment.

The hydraulic fracture was performed utilising a stimulation vessel constructed in 2013 that is equipped to perform large-scale acid and proppant hydraulic fracturing and acid matrix stimulation treatments. This treatment was the first massive proppant hydraulic fracturing operation performed by the vessel. Prior to this operation, the vessel had been used to perform numerous acid-based stimulation operations.

A total of 365.3 metric tonnes (730,536 lb) of resin-coated intermediate strength proppant was placed in the fracture, which is thought to be the largest single fracture treatment ever pumped in this particular national sector of the southern North Sea. A tip-screenout design was successfully used to achieve a high average proppant concentration of 23 kg per square metre (4.7 lb/ft2), which equates to an average propped width of 1.3 cm (0.51 in). The large width was needed to achieve sufficient fracture conductivity for the expected reservoir permeability and to minimize convergent flow pressure drop in the fracture, due to the short perforated interval that was used. A very short perforated interval was used to minimize the risk of near-wellbore problems, due to the well deviation of 40 degrees in the payzone. This approach was successful, as the treatment was pumped as per program with no vessel NPT and no HSE incidents.

Lessons learned included optimisation of perforating operations, methods to better optimise initiation of proppant flow to the blender, rationalising data sources, and effective use of equipment redundancy to ensure zero NPT.

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