Exxon Production Research Company

The Offshore Company

Leo Donald Maus

Joe K Heilhecker

Lyle D Finn

William T Ilfrey

Charles Emory Barton

A hybrid offshore structure for conducting petroleum drilling and producing operations in very deep waters is disclosed. The structure consists primarily of a substantially rigid lower section extending upwardly from the bottom of the body of water to a pivot point located intermediate the bottom and the surface of the body of water, a compliant upper section extending upwardly from the pivot point to a deck located above the water surface, pivot means located proximate the pivot point and adapted to permit the compliant upper section to pivot laterally in response to environmental loads, and torsion means adapted to transmit torsional loads from the compliant upper section to the substantially rigid lower section. The lower section may comprise either a conventional trussed steel frame fixed to the bottom of the body of water by a plurality of piles or a concrete or steel gravity base. The compliant upper section may optionally be either a guyed tower or a buoyant tower. A variety of suitable pivot means and torsion means may be used. The pivot point is positioned so that the weight of the hybrid structure is substantially minimized while maintaining the flexural vibration period of the structure within acceptable limits. Generally, the pivot point will be located above the bottom of the body of water a distance of between about 10 percent and about 50 percent of the total depth of the body of water.

Hybrid offshore structure

A marine riser system for use in deep water drilling operations from a floating vessel is disclosed. The riser system permits detachment of the lower end of the riser from the wellhead enabling the riser to be set aside to a position which is clear of the wellhead. Support means adjacent the wellhead can be used to support and position the riser when it is set aside. Tensioners, support mechanisms and guidance means are provided to move the riser back and forth between the wellhead and support means. In this manner, casing and tools having diameters larger than that of the riser can be inserted into the wellhead without returning the riser to the surface. Drilling operations with large diameter drill bits can also be conducted with the riser in the set aside position.

Riser set-aside system

An improved offshore drilling method and apparatus are disclosed which are useful in preventing formation fracture caused by excessive hydrostatic pressure in a drilling riser. Gas is injected into the riser to provide the lift necessary to return the drilling fluid to the surface and to reduce the density of the drilling fluid. The rate of gas injection overlifts the drilling fluid to the extent that the pressure of the fluid is reduced to less than that of the seawater surrounding the riser. Seawater is permitted to flow into the lower end of the riser in response to the differential pressure between the drilling fluid and seawater so that the pressures of the drilling fluid and the seawater approximately equalize.

Gas lift system for marine drilling riser

An improved offshore drilling method and apparatus are disclosed which are particularly useful in preventing formation fracture caused by excessive hydrostatic pressure of the drilling fluid in a drilling riser. One or more flow lines are used to withdraw drilling fluid from the upper portion of the riser pipe. Gas injected into the flow lines substantially reduces the density of the drilling fluid and provides the lift necessary to return the drilling fluid to the surface. The rate of gas injection and drilling fluid withdrawal can be controlled to maintain the hydrostatic pressure of the drilling fluid remaining in the riser and wellbore below the fracture pressure of the formation.

Artificial lift system for marine drilling riser

Method and apparatus for determining on board a heaving drilling vessel, the flow rate of drilling fluid flowing from a well hole and into a telescoping marine riser connecting the well hole with the vessel. A measuring apparatus is associated with a drilling fluid return conduit of the riser in such a position that the measuring apparatus and the portion of the conduit between the measuring apparatus and the riser are at all times filled with drilling fluid. The measuring apparatus generates a first signal proportioned to the flow rate of drilling fluid flowing therethrough, measures the drilling fluid level in the riser and generates a second signal proportional to the change in volume of the drilling fluid contained therein above the point at which the conduit intersects the riser. The telescoping movement of the riser is measured and a third signal is generated proportional to the change in volume of the flow path provided by the riser between the well hole and said point. The first, second and third signals are correlated with each other whereby the measured flow rate of the drilling fluid is modified to compensate for the telescoping of the marine riser and the drilling fluid stored in the marine riser above the point the conduit intersects with the marine riser, whereby the true flow rate of the drilling fluid flowing out of the wellhole and into the marine riser is determined onboard the heaving vessel.

Growing community of inventors

Houston, TX, United States of America

Leo Donald Maus