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Abstract Control lines hydraulically operated downhole isolation valves were run with the production casing strings of big bore offshore gas producers to provide downhole isolation for losses and pressurised mud cap drilling (PMCD) operations. The mandrel casing hanger was re-designed and manufactured to allow hydraulic controls through the casing hanger and wellhead with a contingency technique to retrieve the control lines. Successful installation on 7 wells provided valuable lessons and confidence in applying such system. The casing hanger and wellhead was re-designed with conduits to install control lines and provide hydraulic communication to external pumps. The wellhead has outlets to retrieve the control lines as contingency. Some design changes to provide better isolation and testing between the two hydraulic conduits were made prior to manufacturing. Workshop trials were done to prove the design. Challenges were resolved during installation with improvements in running control lines below the hanger and retrieving the control lines without nippling down the Blow Out Preventor (BOP). Both primary and contingency techniques were applied successfully after running and landing the casing allowing the downhole casing isolation valve to be operated. Challenges during installation were damage to seals on the hanger and modifying design to retrieve the control lines without having to nipple down BOP and to pick up the casing hanger (after landing) were applied as improvements on job execution. Cementing operations with the casing hangers were successful without issues on the control lines or hydraulic conduits. Expansion of hydraulic fluids from the control lines that leak off when wells were on production at high gas rates were observed and resolved by replacing the bleed-off needle valves. The re-designed casing hanger and seals with the hydraulic outlets are working as designed with no well integrity issues even with the wells producing at high gas rates. The successful installation and production of the wells show that casing hangers with hydraulic communications to control downhole valve on casing string can be used. Successful installation of casing hanger with hydraulic communication to operate downhole valves in casing strings provide opportunities to add devices for casing strings to have more functions e.g., hydraulically set selective seals or packers, sleeve for stage cementing. Instead of hydraulic line, electrical or conductor type lines can be run on casing string for monitoring downhole pressures, temperatures, flow or other parameters outside the casing using similar casing hangers.
Yeow et al. (Thu,) studied this question.