Blowout Preventer Stack Research Articles

Special Guide Bases for the Gulf of Alaska

This paper discusses the designs of two medal guide bases developed for part of the Gulf of Alaska. Required support capacity of a guide base is part of the Gulf of Alaska. Required support capacity of a guide base is compared with predictions of the bearing capacities of Gulf of Alaska soils using published soil bearing capacity relationships and soil shear-strength data. Field measurements during installation of one base indicate satisfactory agreement between predictions and performance. Introduction One of the most important steps when drilling a well from a floating rig is the installation of the 30-in. conductor and permanent guide base. This string must be set essentially vertical and at a depth that will support the overhead and blowout preventer stack. In areas outside the Gulf of Alaska, the 30-in. conductor always has been installed using one of two commonly used methods. Usually, the process involves setting a temporary guide base on the process involves setting a temporary guide base on the sea floor, drilling a 36-in. hole, landing the 30-in. conductor with the permanent guide base on the temporary guide base, and cementing the conductor back to the sea floor. In areas where the soils are too weak to support the temporary guide base, the 30-in. conductor could be jetted to the required penetration. Unfortunately, neither method can be used in a significant portion of the 1976 Gulf of Alaska OCS (outer continental shelf) sale area.In part of this area there is an unconformity at or near the sea floor that separates a hard overconsolidated silty clay from a very soft marine clay. The soft clay varies in thickness from a few feet to about 100 ft in the areas of interest. The soft clay is too weak to support a conventional temporary guide base. The 30-in. conductor cannot be jetted to the required penetration because the silty clay is too difficult to get through and the soft soil is too thin to provide the required penetration. provide the required penetration. Special Guide Bases for the Gulf of Alaska Two special temporary guide bases have been developed to permit drilling in areas that cannot be drilled conventionally. Figs. 1A, 1B, 2A, and 2B are conceptual drawings that also show the bases during installation and after drilling the 36-in. hole and installing the 30-in. conductor and permanent guide base.The floating base is shown in Figs. 1A and 1B. The base is a 15- x 15- x 10-ft-high water tight box that derives much of its support by floating in the soft soils at the soil-water interface. When filled with water, the base weighs 84 lb/cu ft, which is halfway between the 104+ lb/cu ft minimum density of the soft soils and 64 lb/cu ft sea water. The 15- x 15- x 10-ft two-piece construction is a good compromise between transportability and maximum size that can be handled on the spider deck of large semisubmersible drilling units.The floating base is attached to a 40-in. conductor that is used to case off most of the soft soils. This base and 40-in. conductor are designed for use in areas where the soft soils range from 10 or 20 ft to 200 ft or more, where the 30-in. conductor could be jetted to sufficient depth without using a temporary guide base. The 40-in. conductor and floating base are run as a unit and are installed by jetting the 40-in. conductor. The 30-in. conductor and permanent guide base are installed by drilling a 36-in. permanent guide base are installed by drilling a 36-in. hole below the 40-in. conductor, landing the 30-in. conductor and permanent guide structure on the floating base, and cementing the 30-in. conductor back to the sea floor. JPT P. 1635

Design Testing of a Blowout Preventor and Controls System For Drilling in 1,000 Feet of Water

Abstract This paper describes the design considerations forselecting a blowout preventer control system and associatedhandling techniques required for drilling in 1,000 ft ormore of water from a semi-submersible drilling vessel. Design, manufacture, fabrication and assembly testing havebeen completed. This system is described and a summaryof test information is included. The control system is entirely hydraulic using eitherhose or remote pilot operated circuits, depending onresponse time required for each control. A steelwire-reinforced hose bundle was designed and built in onecontinuous length to allow operation without extra support orguidelines. Handling techniques have been developedwhich should allow the control equipment to be run andretrieved without pulling the marine conductor. A unique unitized triple ram blowout preventer unitwas designed and built so that the over-all height of thedrilling control wellhead could be reduced to allow it tobe used with existing vessels. Other components such asthe control panel, hose reel, kill and choke line assemblesand underwater hydraulic connectors are discussed. Introduction The problem was to secure a blowout preventer systemcapable of drilling in all water depths up to 1,000ft or more. Previously used control systems werereviewed to determine what blowout preventer experiencewas directly applicable and what modifications or newdevelopments would be required. In addition, this studytook into account the sea conditions existing along theWest Coast where this system will be tested. Maximumstorm conditions in this area include wave heightsexceeding 40 ft, current in excess of 3 ft/sec and windsin the range of 100 mph. Continuous operation underthese conditions is not a requirement, but the equipmentselected must survive the wave forces and rig motionwhich may occur during these storms. As explained inthe report, the primary control linkage between theblowout preventer stack and the vessel is to be attached tothe marine conductor. Successful operation of the marineconductor is assumed during the discussion of thisprimary control linkage. This report reflects the effects of sea environment onthe controls, reviews the developments required anddescribes the final system which is now awaiting drillingtests. This review places many of the significant designfactors for a subsea blowout preventer system andassociated operating techniques in one place. There maybe disagreement with the equipment and techniquesselected, but the effect of the severe environment (depthand sea conditions) on the design should be appreciated. Hopefully, additional design criteria concerning thevitally important blowout preventer operation will bepresented by others as it is revealed both by experienceand study. Analytical solutions for design problems were usedseveral places. Some of these data are to display theorder of magnitude to be expected rather than to be usedfor detailed design. In some cases data are restricted toa particular item, good only for that item but furnishingcharacteristics which may be expected from similar items. Many times, however, simple tests provided adequatedesign information with much less effort. For instance, fullscale tests of the control circuits were used to evaluatethe feasibility of remote, pilot operated hydrauliccontrols. Design data for the control hose bundle wereobtained by subjecting a full-sized prototype bundle tomaximum forces calculated to exist during actualoperation. Finally, full scale land assembly tests of theequipment were accomplished to further check handlingand operational characteristics. General Description The equipment to be used in this blowout preventersystem will be identified in ascending order, from thesub sea wellhead to the control equipment located on thedrilling vessel. A symmetrical four line system will beused to guide the blowout preventer stack and otherdrilling equipment to the wellhead. One of the basicdesign criteria was that the control system should be inplace and fully tested on the spider beams of the vesselbefore the stack was lowered into position. Theblowout preventer stack will normally be lowered andretrieved while attached to the marine conductor. JPT P. 1023ˆ

Marine Drilling and Well Completions from Floating Platforms

SHIELDS, C.M.; STANDARD OIL CO. OF CALIFORNIA, SAN FRANCISCO, CALIF. Abstract Floating drilling vessels and barges have been used extensively in California coastal waters for core drilling since the early 1950's. The techniques developed in these operations have recently been used for full- scale drilling operation, and some wells have been completed on the ocean floor as successful producers. The floating drilling vessel technique, although still in an early state of development, provides a method for economically exploring deep-water areas; developing marine reserves when additional platforms cannot be justified; and performing exploratory and developing drilling in remote arias. The limitation on the method are in deep diving, vessel mooring systems and high drill pipe and casing stresses caused by vessel movement. Introduction The purpose of this paper is to review the recent developments and accomplishments of the floating drilling vessel techniques, compare the relative economics of developing marine oilfields from floating and fixed platforms, and to examine the risks and intangible advantages in drilling from floating vessels. Drilling operations from floating barges may be divided into three phases. The first phase, starting shortly after World War II, was concerned with obtaining shallow cores in water depths to approximately 100 ft. For the most part cores were obtained using punch or jetting methods, although some work was done with small rotary rigs operated "over-the-side" of small vessels. During this phase over 500,000 ft. of 4 to 6 in. diameter core holes were drilled to depths of 500 ft. below the water surface. The second phase of the floating drilling operations was started about 1954. This phase was initiated with the construction of medium size, 150- to 200-ft vessels employing regular rotary drilling equipment mounted on the center line of the vessel. Ten- to 12-ft holes were cut in the vessel hulls, through which the drilling operation was performed. Operating through the center of the vessel, rather than overside, minimized the effect of vessel roll and pitch and substantially improved the over-all drilling operation. During this second phase, as many as six floating drilling vessels were in service off the California coast. Operations were conducted in water depths to 400 ft and holes drilled to 10,000 ft below the water surface. Drilling operations were also conducted in other areas with shallower water. The third phase of the floating drilling operations was started about 1958 and continues to the present time. This phase is characterized by a further refinement in the drilling technique and development of ocean-bottom drilling equipment, by which wells have been completed on the ocean floor as successful producers. During this phase, new, large drilling vessels have been developed for operations in water depths beyond 300 ft and for drilling to 15,000 ft as efficiently as land or fixed-platform equipment. Description Of Drilling Method The procedure in drilling from a floating vessel is in many respects similar to drilling from a fixed platform or land location. The principal difference, however, is in accounting for the relative motion between the vessel and the ocean floor, caused by currents, wave motion and the inherent springing characteristics of the mooring system. Drilling methods and equipment used with floating vessels have been improved in recent years, although the basic method is essentially unchanged. As shown in Fig. 1 the ocean bottom equipment usually consists of a base plate or template, blowout preventer stack, disconnect coupling, flexible joint, riser pipe and telescopic joint. Guide lines attached to the template provide a means of re-entering the hole during the initial drilling operation. During subsequent drilling operations the riser pipe is used for guiding pipe and tools into the hole as well as providing a conduit for drilling fluid returns. The flexible member and telescopic joint are required to accommodate the lateral and vertical motion of the moored vessel. Disconnect couplings as shown in Fig. 1 are installed above and below the blowout preventers. The upper disconnect joint will permit the riser and associated equipment to be removed for repairs and replacement without disturbing the blowout- preventer assembly. This connection may also be disengaged when operations are secured because of storms and sea conditions. JPT P. 605ˆ