Page 41: of Offshore Engineer Magazine (Aug/Sep 2016)

40 42

that are API 17G compliant, which can

The Oceaneering Millennium ROV is connecting the ? ying leads from the well

SUBSEA be actuated from the surface, or auto- stimulation tool to the subsea tree.

matically close if unexpected pressures are encountered. The system can be con? gured to perform 10K psi or 15K psi stimulations as required.

The system has an emergency quick disconnect system (EQD) that enables the vessel to disengage from the well with zero leakage. The EQD can be released using an ROV, via an electric control line, or with a deadman cable that acti- vates the EQD in case of loss of station keeping or a black ship situation.

Advantages of rigless systems

Unlike rig-based interventions that must access the wellhead vertically, there are several options for connecting the well

Case studies stimulation tool to the subsea wellhead.

It can be deployed and landed using a A subsea well in the Gulf of Mexico mud mat, or secured to a suction pile experienced a signi? cant drop in installed in advance of the stimulation production due to formation impairment. then attached to the wellhead with a A rigless stimulation was performed ? ying lead. On vertical trees, the well from an MSV, using a wellhead stimulation tool uses an H4 connector stimulation tool to bullhead 1100 bbl of directly to the tree. On horizontal trees, acid at 11K psi at the tree. Despite bad the H4 connector is connected by a ? y- weather, the stimulation was completed ing lead to a choke interface. Another in 18 days (including three days of advantage of Oceaneering’s rigless pumping), for $15 million less than a rig- method over rig-based interventions is based operation, and improved the well’s its ability to perform the stimulation on productivity by 75%.

horizontal trees without removing the Also in the Gulf of Mexico, produc- crown plug in the tree. Plug removal tion from two wells in 4300ft of water is needed for the drill pipe used for rig was impaired by ? nes migration. The stimulations to engage vertically with operator determined that each well the wellbore. Using this method, a vari- needed a treatment schedule pumped ety of interfaces are available including within 15 hours at volumes exceeding a choke inserts and high ? ow manifolds, single vessel’s capacity using premixed which do not require plug removal. chemicals. A rigless stimulation was carried out using an MSV and a second,

Rigless intervention capabilities low-pressure pumping vessel. Bulk

Currently, the rigless stimulation treatment chemicals were mixed on the method can treat wells at high pumping ? y during stimulation. The operation

The well stimulation tool deployed rates up to 15K psi with open water was completed successfully and pro- subsea in the Gulf of Mexico.

dual coiled tubing riser units. With duced higher production numbers than this process, the subsea tree can be stimulation. Oceaneering’s production originally anticipated.

Offshore Ghana, an operator deter- controlled from the vessel through enhancement team provides project mined that production from ? ve subsea an umbilical distribution system that management, engineering, and offshore wells had dropped signi? cantly be- provides power and communications service technicians speci? cally trained cause of accumulation of ? nes, calcium to the tree locally, without relying on to integrate all in-house and third-party carbonate and scale. A dual-vessel, control from the distant host facility, services. This provides for the con- rigless stimulation was performed, and can close safety valves as required. sistent execution of well stimulation combining the capabilities of an MSV

During operation, real-time topside and activities, strong customer support, and and a construction vessel. Four open subsea data is streamed back to shore, reduces offshore downtime.

water dual coiled tubing riser units including pump pressure data, ROV Since 2009, more than 30 rigless well were used to pump the treatment video, pressure transducer and ? ow stimulations have been completed suc- chemicals at 16 bpm to a specially meter readings. cessfully in waters as deep as 6700ft in modi? ed well stimulation tool. Each of single and dual-vessel applications, re-

Project management yields results the wells in the ? ve-well campaign saw sulting in average production increases

Project management is an impor- of 50% and savings of as much as 50% an average production rate increase of tant aspect of successful subsea well compared to rig-based stimulations.

more than 70%. oedigital.com August 2016 | OE 43 042_OE0816_Subsea3-Oceaneering.indd 43 7/23/16 12:00 AM