9 In bf'f'shore petroleum operations, it is essential to establish or re-establish physical communications with a subsea system. Divers accomplish this task in relatively shallow water. However, as oil operations move to deeper water and more adverse environmental conditions, diving in many instances has become very difficult. These conditions have led to the investigation of methods for remote establishment of communication and installation of equipment. One such operation involves installing guidelines on suspended exploration wells in the deep waters of the Santa Barbara Channel. This is considered a typical example of the requirements for establishing communication between a vessel and a subsea system. This paper is restricted to the acoustic instruments commercially available and the mechanical equipment designed to install the guidelines.
To establish communications between a vessel and a subsea system, whether operation is active or suspended, requires three steps:
locating the general area by navigational techniques
locating the exact point of entry and
completing the process by mechanically establishing physical communications.
This discussion is limited to the details of Steps 2 and 3; however, an inaccurate navigating system 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, a brief discussion of the over-all system will be presented first. A description of the available acoustic devices will be followed by a discussion of the mechanical equipment. Finally, the mating of both systems for testing will be discussed in detail.
The 'guideline re-establishment system consists of a drill string assembly, lowered from a drilling vessel that is anchored in the near vicinity of the well, and an ocean-floor assembly consisting of a corrosion cap, guide tube, and reflector mounted on the wellhead within the guide structure (Fig. 1). The drill string assembly contains the acoustic device and all four guidelines to be installed. In practice, the vessel is positioned by moving in response to signals from an acoustic device so that the drill string assembly is directly over the ocean floor assembly and ready for stabbing. When stabbed, this drill string 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 BOP and riser. Before any of this can happen, however, the wellhead must be located.
