This paper provides an overview of the ExxonMobil Diana/Hoover offshore installation, including both surface and subsea components in a record water depth of 4,850 feet.

The use of equipment advancements and industry firsts are presented together with a description of the organization and management of the project. The paper concludes with an overview of performance results and lessons learned.

Installation Overview

The installation of a Deep Draft Caisson Vessel (DDCV) drilling and production facility with related subsea pipelines and components in record water depths presented unique installation challenges, which required technology development, equipment advancements and a novel execution approach. Some of the "Industry Firsts" achieved were 1) the heaviest lifts onto a floating structure in open waters, 2) the deepest and largest Steel Catenary Risers (SCRs) installed 3) the largest mooring system installation, and 4) the heaviest lifts onto any type structure in the Gulf of Mexico.

The equipment advancements associated with the project included mooring system handling equipment, a two station J-Lay tower that installed the majority of the flowlines and SCRs, and a "long tether" pipeline touchdown monitoring ROV located on the pipelay vessel.

The 950+ man-year installation mostly occurred during the winter months of 1999/2000 in an area that routinely experiences high velocity eddy currents. These environmental conditions presented safety and operational issues that challenged the Diana/Hoover Construction vessels, which were among the largest in the world.

The execution approach was focused on selection of the most qualified Contractors working predominately under a risk sharing contract structure. A co-located integrated project team organization with common priorities was utilized to manage the offshore execution program. The team was expected to make decisions that were considered in the best interest of ExxonMobil (EM), the individual contractors and the overall project.

The components installed as part of this project are shown in Figure 1. The following sections provide additional detail regarding the platform and subsea installations.

Surface Components

The surface components installed included the DDCV hull, lower and upper deck modules, and various other packages that were lifted into place offshore. This work occurred over a 70 day period, with the Saipem S-7000, the world's largest semi-submersible crane vessel (SSCV), being utilized as the primary construction vessel.


The DDCV hull (Fig. 2) was 705 feet long, 122 feet in diameter and weighed 35,000 tons. It was fabricated in two sections in Pori, Finland, and each section was dry transported by heavy lift vessel to Corpus Christi, Texas. The two hull sections were joined in Corpus Christi and wet towed to site in the horizontal configuration. Once the hull arrived offshore it was prepared for upending and mooring.

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