Deep water diverless technology has been successfully applied to shallow water drilling operations in hostile environments of the North Sea to minimize lost rig time. This technology encompasses currently available instruments and equipment, with state-of-the-art design, and operations procedures. The use of sector scanning sonar, acoustic positioning sys terns, and silicon intensified target, low-light level subsea T.V. cameras to position rigs and install underwater templates is described. Design principles, which allow the diverless installation of templates and underwater wellheads, are discussed. The utilization of deep water operating procedures on two shallow water locations in the North Sea are also described. The economic advantages of using deep water technology in these locations is illustrated.
There are many places in the world where drilling and production operations in shallow water are seriously hampered due to hostile environments which impose severe limitations on diving operations. Deep water technology was developed to provide solutions to problems associated with the inaccessibility of' on-bottom sea floor equipment, poor underwater visibility, and the physical limitations of divers. This technology, which includes currently available equipment, design principles and operations procedures, can be judiciously applied to shallow water operations to realize substantial savings in rig time by expediting completion of predrilling wells through templates for early production.
In the southern North Sea, Amoco (U.K.) Exploration Company and Amoco Netherlands Petroleum Company have been pre-drilling wells through templates supported on exploratory wells in shallow water. Well protector jackets are subsequently installed and the wells tied back. This development drilling program was seriously hampered initially by persistant storms and severe currents.
The hard, sandy seafloor required the jack-up rigs to be positioned precisely in their original deep foot prints, created during the exploratory drilling, to provide rig stability and avoid possibly disasterous lateral loads on the legs. Precise rig positioning was also required in order to reach all of the template well slots. The current conditions of 3 to 5 knots were so severe that the rigs could not be towed onto location, while simultaneously maintaining the proper heading to insure spud can foot print coincidence and avoid damaging the existing well.
Installation of the drilling template was also hampered by the severe currents. Sand and silt entrained in the water reduced underwater visibility for standard subsea T.V. cameras and divers to near zero. Diver on-bottom time is limited to approximately one hour per day during the tide changes; and anything lowered into the water is pushed off target by the strong current. The footings of bottom-founded templates experienced excessive scour, resulting in unacceptable tilting.
Running 30-inch casing was another major problem because of large current-induced deflections, zero visibility, and lack of diver assistance. Eight to ten foot deflections at the end of the 30-inch casing frequently prevented stabbing the casing through its well slot in the template.
