Abstract Transocean Offshore has designed their newbuild drillship Discoverer Enterprise to drill in up to 10,000' of water. The current deepwater drilling record is 7,612'. This paper addresses the equipment upgrades and corresponding additional investment required to outfit a newbuild drillship' for 10,000' of water versus one outfitted for 7,000', which approaches the current limit of existing rigs. Much of the equipment selected for the Discoverer Enterprise had not previously been built in the size or capacity rating required to operate in 10,000' of water. Some upgrades, such as the riser, impacted several other items such as the rotary, buoyancy, tensioners, derrick, and hoisting equipment. In most cases it would not be practical to retrofit existing deepwater rigs for 10,000' of water. The technology developed setting water depth drilling records worldwide in the last 20 years is being applied and expanded operate successfully and efficiently in 10,000' of water. Introduction The Discoverer 534 is the current deepest water depth rated rig at approximately 7,800'. Equipped with 21" riser and an 18 3/4" BOP stack, it holds the water depth drilling record of 7,612' set in the Gulf of Mexico in 1996. The Discoverer Seven Seas has drilled in 7,520' of water, but this was using a 16 3/4" BOP stack and nominal 19" riser. Using riser smaller than 2 I" allows drilling rigs to get in deeper water depths without upgrading their equipment, but that will not be considered since the merits of using a 21" riser system are well documented. In addition to the Discoverer 534 and Seven Seas, there are other rigs nominally rated to water depths of approximately 7,000' that have not had the opportunity to demonstrate their capability. The typical drilling equipment found on a deepwater drilling rig such as the Discoverer 534 or the Discoverer Seven Seas is summarized as follows:0.625" wall riser with 2000 kip couplings, 3" ID 15 ksi choke and kill lines44" - 47" OD riser buoyancy (riser is fully outfitted with buoyancy)16 X 100 kip wireline riser tensioners1 X 3000 HP drawworks using I 3/4" drill line3 X 1600 HP Mud Pumps650 ton derrick capacity49 1/2" rotary table and diverter housing400 or 600 kip in-line heave compensator These vessels are about 534 feet long, have an operating variable load of approximately 7500 tons, and are equipped with six 2500 HP thrusters for dynamic positioning. The vessels' size, equipment, capacities and basic structural limitations all combine to limit their water depth capability to approximately 8,000'. The basic reason for this limitation is their inability to effectively store, run, and support long strings of the type of riser needed for water depths in excess of 8,000'. Operators are now looking to deeper water depths due to the success seen in the last few years between 3,000' and 6,000'. Improved seismic technology has increased the deepwater potential for discovering commercial reserves. High permeability reservoirs and improved completion technology has made flowrates of 20,000 BOPD from oil wells and 100 MCFD from gas wells possible. There are currently 485 blocks leased in greater than 7,000' of water in the Gulf of Mexico.
Mooring and Riser Management In Ultra-Deep Water and Beyond Darrel K. Pelley; Darrel K. Pelley Transocean Search for other works by this author on: This Site Google Scholar Riddle E. Steddum; Riddle E. Steddum Transocean Search for other works by this author on: This Site Google Scholar Andrew S. Westlake Andrew S. Westlake Transocean Search for other works by this author on: This Site Google Scholar Paper presented at the SPE/IADC Drilling Conference, Amsterdam, Netherlands, February 2005. Paper Number: SPE-92616-MS https://doi.org/10.2118/92616-MS Published: February 23 2005 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Pelley, Darrel K., Steddum, Riddle E., and Andrew S. Westlake. "Mooring and Riser Management In Ultra-Deep Water and Beyond." Paper presented at the SPE/IADC Drilling Conference, Amsterdam, Netherlands, February 2005. doi: https://doi.org/10.2118/92616-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE/IADC Drilling Conference and Exhibition Search Advanced Search AbstractIn recent years, offshore oil and gas exploration has rapidly advanced to record water depths that were beyond conception 20 years ago, with the 10,000-ft water depth barrier hurdled in 2003 in the US Gulf of Mexico. Drilling equipment design and capability to achieve this record has simply grown to meet increased capacity requirements.This paper outlines the mooring and drilling riser management challenges that will need to be realized in 10,000 feet of water and beyond. By defining the boundary conditions for moored and dynamicallypositioned scenarios in future record water depths, the challenges to the design and operation of mooring and riser systems can be explored, including component design issues, deployment techniques and system management in adverse environmental conditions. Previous work undertaken on this subject by Transocean shows that the capabilities used to break the 10,000-ft barrier will require yet another step-change to drill in water depths of 12,000-ft (DP) or 10,000-ft (Moored) with conventional subsea well control equipment and marine drilling risers.Two scenarios are presented, one each for moored and dynamically positioned vessels to demonstrate the requirements that require special consideration for successful operation and management of mooring and marine drilling risers.IntroductionThe purpose of this document is to outline the potential use of emerging technologies in marine drilling riser systems and deepwater mooring systems to meet the challenges of the coming years in the deep-offshore drilling industry. Drilling operations in the US Gulf of Mexico (US GOM) in a water depth of 10,011 feet by the Discoverer Deep Seas in November 2003 have provided indications that the ability to perform efficiently and successfully in water depths beyond 10,000 feet requires study of new technologies to enhance the capabilities of existing equipment in lieu of simply scaling up existing systems to meet the increased capability demands.The issues with the conventional steel marine drilling riser appear principally to be mass and wet weight, and several new or emerging technologies were considered as candidates for study in the theoretical 12,000 ft. case. These included but are not limited to the use of composites, including the all-composite riser and composite peripheral lines; aluminum/titanium riser strings; the application of the free-standing riser system and surface BOP methodology (which has been successfully used in ultra-deep water depths with a dynamically positioned MODU). While all of these options have real benefits, some of which are yet to be fully quantified, a decision was made to concentrate on the use of composite peripheral lines on a steel riser tube for several reasons. In particular, the replacement of existing choke and kill lines on an existing deep water riser system represents a substantial reduction in capital investment over the purchase of an entirely new riser system. Additionally, risk is comparatively small since the ability to revert to conventional auxiliary lines is retained. Also of concern is the trend toward higher anticipated mud weights in ultra-deep water wells which not only increase the tension requirement but also result in high local loads in the riser couplings along the length of the riser string. Keywords: riser, upstream oil & gas, operability, coupling load, calculation, catenary system, riser string, minimum line, water depth, wet weight Subjects: Pipelines, Flowlines and Risers, Risers This content is only available via PDF. 2005. SPE/IADC Drilling Conference You can access this article if you purchase or spend a download.
Abstract In recent years, offshore oil and gas exploration has rapidly advanced to record water depths that were beyond conception 20 years ago, with the 10,000-ft water depth barrier hurdled in 2003 in the US Gulf of Mexico. Drilling equipment design and capability to achieve this record has simply grown to meet increased capacity requirements. This paper outlines the mooring and drilling riser management challenges that will need to be realized in 10,000 feet of water and beyond. By defining the boundary conditions for moored and dynamically-positioned scenarios in future record water depths, the challenges to the design and operation of mooring and riser systems can be explored, including component design issues, deployment techniques and system management in adverse environmental conditions. Previous work undertaken on this subject by Transocean shows that the capabilities used to break the 10,000-ft barrier will require yet another step-change to drill in water depths of 12,000-ft (DP) or 10,000-ft (Moored) with conventional subsea well control equipment and marine drilling risers. Two scenarios are presented, one each for moored and dynamically positioned vessels to demonstrate the requirements that require special consideration for successful operation and management of mooring and marine drilling risers.
ABSTRACT Successful Surface BOP drilling operations from moored semisubmersible drilling rigs of Transocean Sedco Forex Inc. have been progressively developed in deepwater regions offshore Indonesia since 1996. These techniques developed specifically for environmentally benign areas have illustrated significant commercial advantages over traditional methods using subsea BOP and low-pressure riser systems. As a result of these proven potential cost savings, significant effort is being focused on developing of similar Surface BOP and high-pressure riser systems suitable for offshore floating drilling applications in more moderate operating environments typical of the Gulf of Mexico, West Africa, Brazil and the Mediterranean. Current industry design guidelines and standards applicable to MODU's are specific to the traditional subsea BOP and low-pressure riser drilling systems. Efforts to develop alternative deepwater Surface BOP technology suitable for moderate environment MODU application have resulted in a requirement for a rational design basis to be established. Development of this technology within the industry is currently fragmented between several groups and an industry-coordinated effort to standardize the design basis and guidelines has yet to evolve. The guidelines presented in this paper evolved from the procedures, equipment, and operational experiences obtained during the successful deepwater Surface BOP drilling operations for the past five years. This experience, combined with various applicable industry deepwater procedures and guidelines is used to develop a methodology to move this technology into moderate operating environments. Further refinements have resulted from HAZOPs, risk analysis and detailed system design along with sound engineering and operational judgement. Implementing the resulting design basis may produce a higher initial capital and operational cost than the benign environment configuration, however, this method achieves or exceeds safety and operational risk factors benchmarked by conventional deepwater drilling operations in moderate environments. The following moderate environment guidelines herein detailed will continue to evolve as the technology advances, but, the established basis of safety to personnel and the environment should remain consistent. INTRODUCTION Simply defined, Surface BOP Operation is the practice of utilizing a floating drilling unit fitted with a BOP that is suspended above the waterline in the moonpool area. The BOP, usually a land/jackup type BOP, is connected to a high-pressure riser serving as a conduit to the sea floor. Typically, the high-pressure riser has been 13-3/8" casing deployed in one continuous length from the casing shoe to the surface wellhead, Figure 1. The equipment configuration is similar to a jackup utilizing added top tension, with the exception the vessel is floating and the water depth may be thousands of feet deep. This concept goes back to the early days of offshore floating drilling. A long-term example of Surface BOP is the Sedco 135A that drilled in the Far East offshore Borneo for over 20 years in water depths as deep as approximately 250 ft. This program began in the 1960's. The Sedco 135 series rigs were triangle shaped submersibles capable of being used in semisubmersible floating drilling applications.
To minimize costs of Beaufort Sea exploration programs, the industry needed a mobile arctic drilling structure that requires little or no site preparation, does not require an active ice defense system, and is suitable for a relatively large range of operating water depths. The Sonat Hybrid Arctic Drilling Structure (SHADS) consists of a bottom-founded, hybrid steel-concrete platform upon which a winterized land drilling rig is placed. The transit draft is approximately 18 feet (5. 5 m), and the unit is designed for operating in water depths ranging from 25 ft (7. 6 m) to 65 ft (20 m). With a prepared berm, the operating water depth can be extended.
The marine riser is the direct link betwen the drilling vessel and the ocean floor. With the expanded economic and political incentives for exploration, the search for hydrocarbons has been extended into increasingly hostile environments. These environments are imposing stresses that may exceed the design limits of an existing marine riser system. One situation that results in high stress is the storm hangoff of the riser and the lower marine riser package (LMRP). To prevent riser failure, the LMRP is unlatched and the riser is hungoff to ride out the storm. If a severe storm coincides with a high-velocity current, the resulting stresses could part the riser. The ideal solution to this problem is to avoid the costly purchase of an improved riser system, yet ensure the survival of the existing system subject to the severe environment loading. There are a few methods to reduce the stress level. One such method is to utilize the advantages of a variable buoyancy system. The two basic riser buoyancy systems are the fixed and variable concepts. Each concept is described. The marine riser is subjected to two stresses: axial compression and moonpool loadings. A variable buoyancy system on the bottom of the risermore » is the most desirable for the prevention of axial compression. To prevent moonpool loading, the riser's hanging weight should be increased, the hydrodynamic drag reduced, the riser physically restrained from contacting the side of the moonpool, and the riser dropped below the moonpool. A variable air-can buoyancy system remains the most practical method to increase the hanging weight of the riser. (DP)« less
Abstract The management of suspended strings of tubulars from floating drilling vessels becomes more critical as operations move into deeper waters, harsher wave, and current environments. Examples of such strings are marine drilling risers during deployment or recovery operations and the running strings for casing or other subsea equipment. An especially important example is the riser and LMRP suspended from a drifting vessel resulting from a forced disconnect event of a dynamically positioned vessel. The analysis of the vertical and lateral response of such strings will be discussed with emphasis on the influence of important parameters such as added mass and damping in the axial direction. The establishment of allowable sea states during deployment and recovery operations will be addressed. A related issue is the length of riser that can be safely left suspended in heavy weather such as hurricanes or North Atlantic storms. Various means of support of the upper end of the string will be examined, especially "soft" vs. "hard" hang-off. The response of the disconnected riser when suspended from a drifting vessel will be discussed with particular emphasis on management of the deflected shape and the reaction of shear loads into the vessel. Introduction It is necessary, during well construction operations from floating vessels, to suspend various strings of tubulars from the vessel. The management of these strings of tubulars becomes more difficult as operations move into deeper waters and more severe environments. Such strings are subject to axial excitation from the heave motion of the vessel and from lateral excitation arising from vessel surge and sway and from wave and current loading. These strings often consist of drill pipe, casing and casing landing strings, marine drilling riser, and landing strings for subsea equipment such as trees. In many cases, these strings are deployed under controlled conditions. The maximum environmental conditions for which the string can be safely suspended are established at the utset of operations and the string deployed only if an adequate weather window exists. In other situations, the strings should be designed to survive the maximum environmental conditions under which well construction operations are conducted. For example, should a dynamically sitioned drill ship lose stationkeeping ability, the marine drilling riser must be disconnected immediately and suspended below the ship. In this case, it would seem prudent that the suspended riser be able to withstand the maximum environment in which it is designed to remain connected. Analysis A thorough analysis of a suspended tubular string would include an investigation of both lateral and axial static and dynamic response of the string including an assessment of vortex inducted vibration (VIV). However, in a large number of cases, a one-dimensional axial analysis may be adequate. Practically all deployment and recoveries are conducted in benign environmental conditions. Although there is usually insignificant lateral response in these cases, the axial response can be substantial. In such cases, a normal mode approach is often used to estimate the axial response of the string. A finite element representation of the riser is used to develop the axial stiffness and consistent mass matrices.
A disconnected riser suspended from a drillship may damage itself or the drillship during storm conditions or high currents. Evaluation of operational limits for long disconnected risers must account for both axial and lateral problems. Frequency domain riser analysis methods are used to predict operational limits for a typical 6000 foot riser with air can buoyancy modules. The effects of venting the air can buoyancy modules on storm survivability of the riser are evaluated for the 6000 foot riser as one method of increasing storm survivability of long disconnected risers.
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