Prototype Testing of the Diverless-Maintained Cluster (DMaC) Subsea Production System
Authors: Pejaver D.R. , Jones J.W. , White John , Brydon Jim 
Published: October 2008

ABSTRACT
Esso Explomtion and Production UK Limited has concluded their Diverless Maintained Cluster (DMaC) Well development program with successfull underwater trials of key hardware and operational concepts.
Efficient ROV tooling together with simple and largely conventional seabed production equipment results in a cost effective cluster well system for water depths ranging between 100m to 1000m.
Novel techniques demonstrated are the diverless installation of flexible pipe using an ROV deployed pull-in tool, and "flytoplace" installation of umbilical jumpers. A multipurpose connector (the "Retlock"), specifically designed for ROV operation, was developed and extensively shop tested.

INTRODUCTION
This paper describes a significant research and development program initiated in 1989and completed early 1992.
The objective of the progmm was to develop a diverlesssubsea production system which would be cost competitive with diver assist systems when deployed in water depths typical of central and northern North Sea locations whilst being suitable for water as deep as 1000 metres or greater, worldwide. The simple and practical principles of cluster well subsea production systems utilised by DMaCemanate from the diver maintained system used on the Shell/ Ilsso "Osprey" field in the North Sea, but adapted for diverless application.
The work was funded by Esso Exploration and Production UK Limited and involved several UK contractors, with technical input and coordination provided by Exxon Production Research Company in the USA. A summary schedule illustrating the overall project plan is presented in Figure I.
This paper summarises the level of development of themajor components of the DMaC system and describes the test program which proved key components of the system by shallow water trials in operationally realistic conditions. A more detailed description of the design basis and philosophies and system components, is given in Reference 1.

DMaC SYSTEM OVRRVIEW
The field scenario assumes oil/gas production from a reservoir sufficiently remote from an export or processing facility to necessitate the use of a gathering manifold. The base case manifold caters for eight wellsgiving a typical equipment layout as shown in Figure 2; the most significant design criteria are presented in Table 1.
The hardware addressed comprised the Xmas trees, manifold, interconnecting jumpers and all related ROV tooling. No engineering work was done on down hole/ drilling items or the main export pipelines or any surface facility.

PRODUCT FLOW SCHEMATIC
The base case DMaC schematic is illustrated in Figure3. Apart from the pigging valve, all hydraulically powered items am mounted on the Xmas trees ratherthan on the manifold.
Well test is by "subtraction". In this method the pigging valve is closed and the effect of switching flow from the production jumper to the test jumper monitoredat the surface facility.

MANIFOLD
The manifold plan area is 5m × 5m (16.4 ft × 16.4 ft)and designed to be installed through the drill rig moonpool. The typical foundation is a single drilled and cemented pile (i.e. similar to an Xmas tree guide base and conductor casing arrangement).