Riserless Light Well Intervention for Deepwater Wells
Riserless Light Well Intervention (RLWI) enables operators to increase the oil and gas recovery rate from subsea oil wells. It allows rapid well access by using smaller DP vessels instead of larger semisub drilling rigs or drillships. RLWI also enables subsea well intervention without having to use a drilling riser package connected to the subsea stack, which is topped by the blowout preventer system. Riserless intervention is a cost-saving alternative to drilling rigs, reducing mobilization time for life-of-well operations including wireline, logging, light perforating, zone isolation, plug setting and removal, and decommissioning. The technology is based on wireline well maintenance, where the cable is routed via a subsea lubricator system into the subsea well. Traditional activities are wireline operations for well logging, perforation and installing or pulling equipment like plugs and downhole safety valve inserts and sensors. The operational envelope can be extended by use of tractors in horizontal wells.
As recovery rate has traditionally been considerably lower on subsea wells than on surface platforms due to more complicated well intervention and maintenance issues. RLWI enables players to perform intervention to increase the recovery rate at significantly reduced time and much less cost. Another positive aspect of employing RLWI services as that no hydrocarbons are transported to the vessel, but flushed back into the well through the lubricator system during normal operations. However, RLWI is a complex operation requiring specialized technical expertise and control in all phases of the preparation and implementation.
Helix Energy Solutions, for example, performs riserless intervention work via its Subsea Intervention Lubricator (SIL), a single trip riserless system that facilitates access to large bore subsea wells, making possible safe and efficient riserless well intervention from a dedicated subsea intervention vessel. These types of specialized vessels lead the subsea vessel market order book and are in great demand at locations where large deepwater exploration programs are ongoing, such as the Brazil, the GoM and West Africa. The Helix SIL’s fully hydraulic control system provides a high level of system reliability and redundancy. The control system is an integrated system connected to the topside hydraulic generation and distribution systems, as well as the subsea systems and third party subsea trees. Remote access to the master control is also available from onshore. According to Helix, when a SIL system is deployed from a monohull vessel, cost savings of between 40 and 60 percent are possible compared to well intervention using a drilling rig.
Helix Energy Solutions Group, Inc., has recently entered into agreements with Petrobras to provide well intervention services offshore Brazil. Helix will be providing the services using 2 newbuild chartered monohull vessels, which will be built at the Flensburger shipyard in Germany for Siem Offshore AS. Helix will provide the topsides and manage the integration of the RLWI equipment onto the vessels, while Siem will be responsible for the monohull build and oversee construction at the shipyard. Siem will be the owner of the vessels, and charter both the vessels and marine crew to Helix for an initial period of 7 years. Helix’s aggregate investment in the topside equipment for both vessels is expected to be approximately $260 million. The initial term of the contract with Petrobras is for 4years with options to extend. The first vessel is expected to be in-service for Petrobras mid-2016, with the second vessel to follow later that same year. It is interesting to note that Petrobras is the lone player offering long-term charter contracts for subsea vessels in Brazil.