document

Abstract

Development well K14-FB 102 was completed as a dual lateral in 1997 to optimise production capacity and reservoir drainage from a tight, Rotliegend sandstone in an offshore gas play in the Dutch sector of the North Sea. The two 5 7/8" horizontal production intervals were drilled and completed openhole using a rheologically engineered, minimal solids, non-damaging sodium formate brine based fluid designed as a drill-in fluid for reservoir intervals. The system was designed around the Low-Shear-Rate-Viscosity (LSRV) which is critical not only for hole cleaning and drilling performance, but also for minimizing filtrate invasion and potential formation damage by using minimal solids. The formate system exhibited superior hole cleaning qualities during the entire interval and no significant drag was observed during drilling. No pills were pumped prior to pulling out of hole and tripping proceeded without problems, verifying excellent hole condition. As a result of high ROP's, a 35% reduction in total reservoir drilling time was achieved. The resulting production capacity was 40% above expectation and a near-zero mechanical skin indicated that the reservoir interval had been completed with minimal residual drilling induced damage. The formate system, with its unique rheological profile, differs from other water-based fluids, and provided advantages not only for drilling technique but also enhanced HSE criteria.

Background

The K14-FB gas field is located close to existing offshore infrastructure. Asset value has been maximised through the deployment of minimal new surface equipment and ‘fit-for-purpose’ well solutions. The field has been developed using mini-satellite platform technology with a subsea umbilical ‘tie-in’ to the existing regional infrastructure. The first development well involved a relatively inexpensive sidetrack and ‘tie-back’ of an exploration well. The second development well was designed to avail of an efficient sub-horizontal openhole reservoir completion, and it was planned to trial the world's first ‘Expandable Completion Liner’ (ECL). However, due to operational difficulties, this completion method was not possible. Instead, the well was completed as a dual lateral with one branch being left barefoot, and the other with a pre-drilled liner (PDL).

Well test analysis in the two exploration wells drilled in the field had already established a poorer than average sandstone reservoir quality (av. effective horizontal permeability 1 - 10 mD) compared with that in neighbouring fields (10 - 100 mD). This necessitated an approach which would ensure minimum wellbore damage, and maximise reservoir productivity from the K14-FB development wells. Sand failure prediction work using core material from the exploration wells indicated that the sandstone was competent and that development wells would not require dedicated sand control equipment.