Guest Editorial: The Future of Subsea Well Access and Completions
Authors: Horvat Damir 
Published: July 2019

Guest editorial
A review of technologies currently applied in offshore environments to drill and complete subsea wells for hydrocarbon production confirms that many opportunities exist to improve methodologies in ways that can be more economically beneficial and more environmentally sustainable.
Most drilling and completion challenges have been met and overcome on a case-by-case basis although collective knowledge, and industry improvements, have progressed rapidly since the late 2000s.
Subsea completions for gathering hydrocarbons from subsea wells have demonstrated both environmental and economic benefits for offshore oil and gas projects. Barriers and opportunities for expanded use of subsea completions involve both technological and regulatory issues. Advanced technologies are needed to ensure long-lived and serviceable subsea•equipment.
Reasonable regulations also are needed to make sure that the best available technologies and practices are considered in•rulemaking that affects subsea operations and future of subsea well access.
Well Completions and Subsea Completions
Completion is used in offshore oil and gas activities in two different contexts. A well completion involves a set of actions taken to convert an individual borehole into an operational system for controlled recovery of underground hydrocarbon resources. A subsea completion refers to a system of pipes, connections, and valves that reside on the sea floor and serve to gather hydrocarbons produced from individually completed wells and direct those hydrocarbons to a storage and offloading facility that might be either offshore or onshore.
Subsea completions typically contain an upper completion, a lower completion, and a production tree. Advances in upper and lower completions followed normal developments in materials, pressure, and temperature ratings. However, significant advancements in subsea well access has occurred in the past few years. The later advancement reduced operational costs and led to the capability to develop one-trip, single-system, umbilical-less installation of tubing hangers.
One of the remarkable accomplishments of the upstream offshore petroleum industry has been the development of technology that allows simplified but efficient subsea well access to carry out the operations in a more complex situation.
Despite an increase in complexity, improvements in subsea well access and completion technology have allowed more complex well patterns to be drilled to a greater depth such that additional hydrocarbon resources can be developed at a greater distance from the drilling or production structure, allowing more energy to be produced with less environmental impact.
In the past 15 years, mechanical subsea systems have been developed, which allow deepwater riserless drilling with weighted mud and with fluid returns to the drilling rig. Those systems allow a dual-gradient hydrostatic pressure to be applied, thereby more closely matching the natural deepwater pressure profile. While those systems have been used on a number of offshore wells, there is limited supply of the necessary equipment and other well-control issues must be carefully considered for each particular operation.