Method and system for maintenance and servicing of subsea wells

A system for servicing a subsea well with its wellhead located adjacent to the ocean floor and production flow lines extending therefrom along the ocean floor comprising:

• a. flexible riser means;
• b. a surface support vessel with means for raising, lowering and attaching the flexible riser means to the wellhead;
• c. means, located on the support vessel, for perform maintenance on the subsea well via the flexible riser means;
• d. a lower riser package attached to the flexible riser means;
• e. the lower riser package including mating and sealing surfaces to releasably engage the wellhead and establish communication between the flexible riser means and the wellhead;
• f. A positive buoyancy portion of the flexible riser means adjacent to the lower riser package;
• g. a neutral buoyancy portion of the flexible riser means, adjacent to the positive buoyancy portion;
• and
• h. the remainder of the flexible riser means having negative buoyancy.

A flexible riser and lower riser package for servicing a subsea well with its wellhead located adjacent to the ocean floor comprising:

• a. the lower riser package attached to one end of the flexible riser;
• b. the lower riser package including means for releasably engaging the wellhead and establishing communication between the flexible riser means and the wellhead;
• c. a positive buoyancy portion of the flexible riser means adjacent to the lower riser package;
• d. a neutral buoyancy portion of the flexible riser means, adjacent to the positive buoyancy portion;
• and
• e. the remainder of the flexible riser means having negative buoyancy.

A flexible riser and lower riser package for servicing a subsea well with its wellhead located adjacent to the ocean floor comprising:

• a. the lower riser package attached to one end of the flexible riser;
• b. a fluid flow passageway extending longitudinally through the lower riser package;
• c. means for connecting the flexible riser means to the upper end of the passageway to establish communication therewith;
• d. blowout preventers to control fluid flow through the passageway;
• and
• e. wellhead connector means on the lower end to releasably attach the lower riser package to the subsea wellhead.

The method of servicing a subsea well with its wellhead located adjacent to the ocean floor comprising:

• a. positioning a support vessel on the ocean surface within a preselected offset from the wellhead;
• b. launching a remotely operated vehicle from the support vessel to locate the wellhead and remove its tree cap;
• c. deploying a flexible riser means with an attached lower riser package into the water from the support vessel;
• d. guiding the lower riser package to the wellhead by the remotely operated vehicle after the wellhead has been prepared;
• e. attaching the lower riser package to the wellhead to establish communication between the wellhead and flexible riser means;
• and
• f. performing maintenance on the subsea well from the support vessel via the flexible riser means.

The method of servicing a subsea well with its wellhead located adjacent to the ocean floor comprising:

• a. positioning a support vessel on the ocean surface within a preselected offset from the wellhead;
• b. launching a remotely operated vehicle from the support vessel to located the wellhead and remove its tree cap;
• c. deploying a flexible riser means with an attached lower riser package into the water from the support vessel;
• d. guiding the lower riser package to the we the remotely operated vehicle after the wellhead has been prepared;
• e. attaching a first line from the lower riser package to the subsea wellhead to measure the distance therebetween;
• the
• f. placing a second line from the support vessel to ocean floor to measure movement of the support vessel relative thereto;
• g. paying out or retrieving the flexible riser means with a powered reel to control movement of the lower riser package towards the wellhead at a preselected rate in response to changes in the first and second measuring lines;
• h. attaching the lower riser package to the wellhead to establish communication between the wellhead and flexible riser means;
• and
• i. performing maintenance on the subsea well from the support vessel via the flexible riser means.

The method of servicing from a support vessel a subsea well with its wellhead located adjacent to the ocean floor comprising:

• a. combining a remotely operated vehicle and a lower riser package into a single unit which can be launched with a flexible riser means;
• b. attaching an umbilical cable to the lower riser package to supply electric and hydraulic power thereto from the support vessel;
• c. positioning the support vessel on the ocean surface within a preselected offset from the wellhead;
• d. deploying the flexible riser means with the single unit attached thereto into the water from the support vessel;
• e. supplying power and control to the remotely operated vehicle portion of the single unit from the umbilical cable;
• f. locating the wellhead and removing its tree cap with the remotely operated vehicle portion of the single unit;
• g. guiding the single unit to the wellhead by the remotely operated vehicle portion after the wellhead has been prepared;
• h. attaching the lower riser package to the wellhead to establish communication between the wellhead and flexible riser means;
• and
• i. performing maintenance on the subsea well from the support vessel via the flexible riser means.