Development of a Diverless Subsea Module Deployment System
Authors: Moore B. , Cretenet A. , Parfitt S.H.L. , Primrose G.M. 
Published: October 2008

ABSTRACT
The paper describes the development of a deepwater guideline less Module Deployment System (MDS), undertaken jointly by BP Exploration's DISPS Project and Elf UK. Design, manufacture and test of two prototype components of the MDS, namely a remotely controlled, negatively buoyant, load carrying underwater vehicle (Remote Guidance Vehicle - RGV) and a Heave Compensation Winch (HCW), was undertaken and is discussed, along with their associated technical risks. A computer simulation of the RGV behaviour is described, along with two interchangeable automatic position controllers and an improved acoustic position measuring system.

INTRODUCTION
For diverless subsea production systems in 350m to 750m water depth, the intervention technology used to install and change out seabed equipment modules will be a crucial element. This paper describes the development of such a deepwater intervention system for BP Exploration's DISPS Project and for Elf UK. Reference 1 gives the overview of this system within the DISPS development.
The primary function of any subsea intervention system is guidance and conventionally this has been achieved with guidelines. In deeper water it was thought that a guideline less approach, using a Remote Guidance Vehicle, might offer considerable advantages, and if successful, would enhance the Industry's capabilities. The high cost of semi-submersible drilling vessels coupled with their slow mobilisation and deployment time, influenced the decision to develop a guidelineless MDS, which could operate from a monohull dynamically positioned (DP) support vessel.
Starting with a definition of the MDS performance requirements, the paper traces the evolution of the system from concept evaluation and preliminary design through to detail design, manufacture, and Factory Acceptance Testing of a Remote Guidance Vehicle (RGV) and Heave Compensation Winch (HCW), which were built to performance test the concept. Attention is focussed on the main technical risk areas and the methods and tools used to evaluate these and build confidence in the design.

TECHNICAL PERFORMANCE SPECIFICATION
The deepwater subsea studies (References 1 and 2) proposed a modular concept for the seabed facilities, and defined the load carrying and guidance requirements of the MDS. Environmental and operating conditions were determined by potential future exploration activity in the deep water west of the Shetland Islands.
System specification requirements including station keeping are summarised in Table 1.

CONCEPT EVALUATION
The requirement for guideline less module deployment dictated the need for the following major components:-A vehicle. to transport .and position modules over the subsea template (Remote Guidance Vehicle).A deployment vessel with station keeping capabi1ity.A deck mounted module handling and deployment system. During concept evaluation the aim was to prepare conceptual designs and perform preliminary analyses, to establish the performance requirements of these major components and the intervention system as a whole.