This paper describes the development of a tight gas reservoir in the Dutch sector of the Southern North Sea, using a horizontal well with 5 hydraulic fractures. The reservoir is tight (average permeability below 0.1 mD) and was discovered in 1986. The first development well was drilled as a long reach horizontal well in 1990, and completed with a cemented liner. The well was perforated and initial production was 0.2 mln Nm3/d after which the well quickly dropped below its liquid loading limit of 0.09 mln Nm3/d. The well was brought back into production 13 years later and produced at a stable rate of 0.07 mln Nm3/d. In 2005 the well was sidetracked using under-balanced drilling in an attempt to intersect natural fractures (Veeken, 2007). The initial production from this sidetrack was 0.1 mln Nm3/d, but this time the well was able to sustain production at 0.07 mln Nm3/d as the tubing head pressure was lower by that time. To develop this reservoir, the well was sidetracked (overbalanced) in 2008 and completed with a cemented liner. In 2009, 5 hydraulic fractures were placed using a jackup support barge and a specially converted supply vessel. Since December 2009 the well has produced steadily at 0.3-0.4 mln Nm3/day, a (steady-state) production improvement factor of 5-6. This was the first true tight gas (<0.1 mD) development in the North Sea using a horizontal well with multiple fractures. The initial production takes place at constant rate and constant pressure, which suggests that significant cleanup is taking place, either in the fracture or the reservoir or both. An attempt has been made to model this cleanup in a 3D reservoir simulation model. This paper describes the background of the project, fracture design methodology, operational issues and lessons learned, fracture treatment data analysis, post fracturing production analysis (with over a year of production history) and production forecast. This paper is a valuable case study for operators and contractors involved in offshore fracturing operations in low permeability gas reservoirs.

Tight gas developments in the high cost environment of the North Sea are becoming economical and operators are focusing on the technology required to realise these plays and extend field and facility life. Operating companies are targeting tight gas reservoirs with low to very low permeability with long deviated and horizontal wellbore sections. Close attention to the perforating method is required in order to optimise hydraulic fracturing operations whilst minimising rig time. Sand jetting technology has been in use by various industries for many years. Although theoretical papers for oilfield applications were published as early as the 1960s (Brown et al, 1960), it was only after advances in steel metallurgy in the last decade that tools could be made robust enough for real-world oilfield use. In addition, simulation software has improved greatly in recent years, yielding better predictability for this type of operation. This paper will describe coiled tubing-conveyed sand jetting perforating operations for a five stage multi-frac horizontal gas well in the Southern North Sea. The goal of the operation was to create perforations with minimal entrance friction, reduced tortuosity during treatment, and minimise the chance of multiple fractures. Such a treatment would reduce the chances of premature screen-out and the associated costly rig time as well as allow for optimised placement of the proppant following a tip screen out (TSO) design. The challenges associated with performing the operation on a small, unmanned satellite platform will be described, along with pre-job planning and operational steps taken to ensure the sand jet tool could reach the target depths in the deviated well.