An Acoustic-Mechanical Method Of Re-establishing Communication With Subsea Systems
Authors: Sheffield J.R. , Masonheimer R.A. 
Published: December 2007

A practical system has been developed for re-establishing guidelines on subsea wells. A commercially available acoustic device is used in conjunction with specifically designed mechanical equipment. Field tests and successful applications are discussed here, as well for using the equipment.

Introduction

In offshore petroleum operations, it is essential to establish or re-establish physical communication with a subsea system. In relatively shallow water, divers accomplish this task. However, as oil operations move to deeper water and more adverse environments, diving in many instances becomes very difficult. Such conditions have led to the investigation of methods for establishing communication and installing equipment remotely. One typical operation involving the installation of guidelines on suspended exploration wells in the deep waters of the Santa Barbara Channel illustrates the requirements for establishing communication between a vessel and a subsea system. In this paper we shall discuss only the commercially available acoustic instruments and the mechanical equipment designed to install the guidelines. To establish communication between a vessel and a subsea system, whether operation is active or suspended, requires three steps:finding the general area by navigational techniques,finding the exact point of entry, andcompleting the process by point of entry, andcompleting the process by mechanically establishing physical communication.

This discussion is limited to the details of Steps 2 and 3; however, an inaccurate navigating system (Step 1) could require long-range acoustic devices (Step 2) that are not commercially available and would have to be built. The design and development of the required mechanical equipment will depend to a certain extent on the acoustic devices available. On the other hand, the job to be done and the hardware needed for the job may indicate a preferable acoustic device. Thus we shall first discuss briefly the over-all system, then describe the available acoustic devices and the mechanical equipment. Finally, we shall discuss in detail the mating of both systems for testing.

Re-establishing the Guidelines

The guideline re-establishment system consists of a drillstring assembly, lowered from a drilling vessel anchored in the vicinity of the well, and an oceanfloor assembly consisting of a corrosion cap, guide tube, and reflector mounted on the wellhead within the guide structure (Fig. 1). The drillstring assembly contains the acoustic device and all four guidelines to be installed. The vessel is positioned by moving in response to signals from an acoustic device so that the drillstring assembly is directly over the ocean-floor assembly and ready for stabbing. When stabbed, this drillstring assembly will orient mechanically, install all four guidelines, then dog into the ocean-floor assembly so that the reflector, guide tube, and corrosion cap can be removed from the wellhead. Thus, when the string has been pulled and the guideline installation system laid down, the well will be clear and ready for running the blowout preventer and riser. Before any of this can happen, however, the wellhead must be found.

JPT

P. 1075