TECHNICAL FIELD

This invention relates to the method of providing a light weight or neutrally buoyant umbilicals for subsea blowout preventer stacks.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

REFERENCE TO A “MICROFICHE APPENDIX”

Not applicable

BACKGROUND OF THE INVENTION

Deepwater offshore drilling requires that a vessel at the surface be connected through a drilling riser and a large blowout preventer stack to the seafloor wellhead. The seafloor wellhead is the structural anchor piece into the seabed and the basic support for the casing strings which are placed in the well bore as long tubular pressure vessels. During the process of drilling the well, the blowout preventer stack on the top of the subsea wellhead provides the second level of pressure control for the well. The first level being provided by the weighted drilling mud within the bore.

During the drilling process, weighted drilling mud circulates down a string of drill pipe to the drilling bit at the bottom of the hole and back up the annular area between the outside diameter of the drill pipe and the inside diameter of the drilled hole or the casing, depending on the depth.

Coming back up above the blowout preventer stack, the drilling mud will continue to travel back outside the drill pipe and inside the drilling riser, which is much large than the casing. The drilling riser has to be large enough to pass the casing strings run into the well, as well as the casing hangers which will suspend the casing strings. The bore in a contemporary riser will be at least twenty inches in diameter. It additionally has to be pressure competent to handle the pressure of the weighed mud, but does not have the same pressure requirement as the blowout preventer stack itself.

As wells are drilled into progressively deeper and deeper formations, the subsurface pressure and therefore the pressure which the blowout preventer stack must be able to withstand becomes greater and greater. This is the same for drilling on the surface of the land and subsea drilling on the surface of the seafloor. Early subsea blowout preventer stacks were of a 5,000 p.s.i. working pressure, and over time these evolved to 10,000 and 15,000 p.s.i. working pressure. As the working pressure of components becomes higher, the pressure holding components naturally become both heavier and taller. Additionally, in the higher pressure situations, redundant components have been added, again adding to the height. The 15,000 blowout preventer stacks have become in the range of 800,000 lbs. and 80 feet tall. This provides enormous complications on the ability to handle the equipment as well as the loadings on the seafloor wellhead. In addition to the direct weight load on the subsea wellheads, side angle loadings from the drilling riser when the surface vessel drifts off the well centerline are an enormous addition to the stresses on both the subsea wellhead and the seafloor formations.

Another complication is that with all the weight and size of the blowout preventer stacks, duplicate heavy umbilicals are required to provide operational control signals to the blowout preventer stacks via duplicate control pods. Especially in deeper water of several thousand feet, the umbilicals are so heavy that they cannot simply be suspended in the water as with weights of 10,000-15,000 lbs. heavy and high capacity winches would be required to handle them. Additionally, during the drilling process in deep water the vessels are characteristically floating vessels which continuously heave with the ocean waves causing a continual dynamic motion on the supporting winch. For these reasons, the heavy umbilicals are clamped to the drilling riser every two or three joints for support.

As the control pods are one of the historical components needing service and maintenance, it is difficult to retrieve a control pod with a very heavy umbilical attached. Typically, the drilling riser and lower marine riser package portion of the blowout preventer stack must be brought to the surface for control pod or umbilical maintenance. This is how the umbilicals have been made for the past 60 years of offshore drilling, and continues to be a problem.

BRIEF SUMMARY OF THE INVENTION

The object of this invention is provide an umbilical for subsea drilling systems which is neutrally buoyant.

A second object of this invention is to allow the recovery of a subsea blowout preventer stack control pod without having to recover the lower marine riser package and without handling a heavy umbilical.

A third object of this invention is provide a connector for the lower end of the neutrally buoyant umbilical connector.

Another object of this invention is to interface the connector with an acoustic control pod on the lower blowout preventer stack.

