Three-dimensional visualization for well placement and geosteering: Njord Field, offshore mid-Norway

Abstract

Njord is a structurally complex Lower Jurassic oil field located on the Halten Terrace, offshore mid-Norway. The field was discovered in 1986 and has been under production since 1997. The field is produced by a combination of depletion and crestal gas injection. Difficulties in finding new economically viable drilling targets led to a drilling stop in 2001–2002 and production is now in decline. A second drilling phase comprising three infill wells began in late 2002. Production results from these three wells will be critical for determining Njord’s future beyond 2005. During the drilling stop, advanced 3D visualization techniques were used to unravel the field’s complex extensional fault pattern. New well targets were identified using multiple seismic datasets and multiple interpretations. 3D visualization was also used during drilling to keep the wells within the reservoir and to avoid an unstable formation. Reservoir simulation models were used to identify areas with undrained potential, and 4D seismic data indicated fault blocks where changes in gas saturation had occurred. The reservoir oil is initially under-saturated, but gas has also come out of solution in areas with significant pressure depletion. Gas has also been re-injected. New wells were planned to avoid these fault blocks. Target points were placed using 3D visualization software and well path dog-leg angles were calculated. The process continued iteratively until a well path had been achieved with maximum reservoir penetration and realistic dog-leg angles (< 3.5°). Real time data were transmitted to shore during drilling using a web service. These data included survey, petrophysical log, biostratigraphical and borehole image data that were used alongside the 3D visualizations. In this way, drilling progress through the G&G interpretation was continuously monitored. Similarly, geosteering, or plug back and sidetrack, decisions were quickly evaluated. Supplementary material: Movies referred to in the article are available at https://doi.org/10.6084/m9.figshare.c.4812936