Abstract
The Gryphon Field (UK Central North Sea) development commenced in 1993 with the successful exploitation of massive sand rich turbidite lobes of the Balder formation by horizontal wells. A component of small scale sand injection had been identified during appraisal and subsequent development but it wasn't until the acquisition of long offset simultaneous inversion seismic data in 2002 that the scale of the injection wing along the eastern edge of the field was appreciated. A full evaluation of the subsurface uncertainties led to the injection wing being matured as a development target although one which presented new challenges.
The main challenge proved to be locating and then geosteering through a three dimensionally constrained target with high lateral positional uncertainty and potential for wellbore instability. A multi-disciplinary team met this challenge with a combination of new technologies (e.g. prototype deep reading and azimuthal resistivity LWD tools) and the rigourous implementation of wellbore stability recommendations offshore.
Further technologies and strategies to mitigate these risks were introduced in the course of the drilling campaign (e.g. directional survey uncertainty reduction by In-Field Referencing and Dual Inclination techniques, landout strategies to address lateral positioning uncertainty, optimisation of well planning involving the multi-disciplinary team in a 3D environment and the use of low-rheology muds).
Production in some of the injection wing wells has substantially exceeded prediction whereas others have been more challenging to produce due to a faster than anticipated water-cut development. When averaged over all the wells, production targets have been exceeded.
The injection wing play has helped rejuvenate the field with seven wells drilled in the structure between 2004 and 2006 which, as of May 2007, have produced approximately 11 million barrels of oil and are contributing 80% of daily production.
