Sustained production in wells with potential variable pressure

The operator's goal was to deliver a sustained 6.8 million m³/d [240 MMcf/d] production rate from three wells in a sandstone reservoir with a limited completion budget. This required a different approach to well design than typically used in other North Sea HPHT developments, where pressure accumulation on the previously cemented annulus has often been a problem.

The drilling team needed to find an application that would eliminate this potential for pressure accumulation, which could cause monitoring problems on a subsea well with undesired wellhead pressure or require costly subsea remedial treatments.

Customized cements provide tight seal and improved well pressure control

The FlexSTONE HT advanced high-temperature flexible cement technology system was used to create a permanent seal above the HPHT formation. Schlumberger proposed using FlexSTONE HT cements because of their flexible nature and high temperature stability. CemSTRESS software provided additional design tools. Displacement modeling proved crucial to effective planning and execution.

As designed, 305 m [1,000 ft] of 1,941 kg/m3 [16.2 lbm/galUS] flexible FlexSTONE HT cement was placed across the interface of the high-pressure formation to effectively provide a gasket-like seal complete with expanding agent behind the production casing string. The inclusion of the expanding agent was designed as a mitigation measure against microannulus creation during casing pressure testing operations.