A method of completing a subsea borehole including connecting a first vessel to a subsea wellhead assembly via a riser. A borehole is drilled with a drill string communicated to the subsea wellhead assembly through the riser. A lower completion assembly is run on a service string into the borehole through the riser. At least two barrier valves of the lower completion assembly are set with the service string in order to form a mechanical barrier to fluid flow with each of the at least two barrier valves. The riser is disconnected from the subsea wellhead assembly. An upper completion string is run through open water to the borehole and connected to the lower completion assembly. An lower completion assembly for a subsea borehole is also included.