IADC/SPE 112388

PRD12,000 Drill Ship; increasing Efficiency in Deep Water Operations Brre Fossli, Ocean Riser Systems; Sjoerd Hendriks, GustoMSC

Copyright 2008, IADC/SPE Drilling Conference This paper was prepared for presentation at the 2008 IADC/SPE Drilling Conference held in Orlando, Florida, U.S.A., 46 March 2008. This paper was selected for presentation by an IADC/SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the International Association of Drilling Contractors or the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the International Association of Drilling Contractors or the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the International Association of Drilling Contractors or the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous ac-knowledgment of IADC/SPE copyright.

Abstract

In the deep water environment large and expen-sive to operate 5th and 6th generation drilling rigs are uti-lized to drill exploration wells, drill development wells, perform completion activities and intervene and work over development wells. In the current market with spiraling day rates new drilling systems and improved functional specifications have been incorporated into a new build vessel of a reduced size, with improved capabilities and with functional specifications that will make drilling and work over intervention of subsea wells more efficient and cost effective against the traditional MODU. The new vessel has the characteristics in size of an earlier generation, but the functionality of the next generation vessel. The application areas are:

Drilling subsea wells with a conventional subsea BOP and marine riser system in up to 5,000 ft water depth and ability to drill deepwater exploration wells with a split BOP and High Pressure (HP) riser system in up to 12,000 ft water depth.

With a unique HP riser and split BOP, coupled with a system for Managed Pressure Drilling (MPD) particularly developed for deepwater subsea drilling, operations are enabled to cover all deepwater areas around the world.

Underbalanced intervention work over and drilling performed through the same HP riser and BOP system.

Motion characteristics of the vessel while in DP over a subsea well that will not compro-

mise activities such as retrieving/landing Xmas trees or completions and/or through tubing drilling.

High transit speed of 12-14 Knots for quick mobilization.

New drainage holes can be drilled with this system in ma-ture areas often made inaccessible with conventional drill-ing technology due to depleted and variable formations pressure. The drilling technology and the fit-for-purpose drilling unit combined may lead well up to 50% well cost reduc-tion compared to 5th or 6th generation MODUs and tradi-tional drilling methods. Introduction

The drilling market will welcome the 6th genera-tion drilling vessels in the coming few years. The 6th gen-eration fleet has followed the trend of the 5th generation with growing into larger and larger units, consequently resulting in more costly units, not only in initial invest-ment and operational costs, but also on sustainability and environmental impact. In the deep water environments these rigs are utilized for deep water operations; drilling exploration and development wells, carry out completion activities and perform intervention and work-over opera-tions on development wells, increasing the cost per well due to their size. The alternative drill ship design philoso-phy as presented here targets to reverse this trend and mi-nimizes rig size to consequently minimize the day rates and improve economics. The alternative design philosophy focuses on the intended function of the vessel trying to get the vessel as small as possible, without compromising the operational integrity of the rig. A typical example of this philosophy is the PRD12,000, in which new drilling technologies are incor-porated, requiring less volume and displacement. Due to the size reduction the design is an effective tool against the spiraling day rates in the current market. The design philosophy and PRD12,000 concept design united with the newly developed drilling techniques of Ocean Riser Systems, also targeting cost reduction per well by increasing drilling efficiency, but also utilizing more efficient equipment requiring a smaller rig. Ocean Riser Systems has developed drilling techniques, utilizing Ocean Riser unique HP riser and split BOP, coupled with the Managed Pressure Drilling system particularly devel-oped for subsea and deep water to enhance operations. The drilling system can also support under-balanced drilling

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and well intervention and work-over activities and is able to access depleted and variable formations pressure.

Ocean Riser Systems and GustoMSC have combined the improved drilling capabilities into the new build design of reduced size, to make drilling and intervention work on sub sea wells more efficient and cost effective against the traditional MODU, saving up to 50% cost per well. The vessel is characterized by the profile (Fig. 1):

Drill deepwater exploration wells with a split BOP and High Pressure (HP) riser system in up to 12,000 ft water depth, whilst still be able to drilling subsea wells with a conven-tional subsea BOP and marine riser system in up to 5,000 ft water depth.

The unique HP riser and split BOP, coupled with a system for Managed Pressure Drilling (MPD) are suitable to cover all deepwater areas around the world.

Under balanced intervention workover and drilling can be performed through the same HP riser and BOP system.

Motion characteristics of the vessel while in DP mode over a subsea well that will not compromise activities such as retriev-ing/landing Xmas trees or completions and/or through tubing drilling.

Drilling new drainage holes in mature areas, often inaccessible for conventional drilling technology due to depleted and variable for-mations pressure.

High transit speed of 12-14 knots for quick mobilization.

Vessel size and equipment optimized for lowest day rate.

GustoMSC drill ship history and design philosophy.

In the 70s the Gusto shipyard developed the first DP drilling vessels with the Pelican class drill ships. A total of 10 Pelican Class units were built by the shipyard, and a total of 15 units were delivered during the 70s and 80s of which 14 are still operating successfully after 30 years of service, some reaching to 6,000 of water depth after several upgrades. The experience built up from the Pelican class designs was used to develop drilling vessels in the 90s for a new gen-eration which resulted in the GustoMSC 10,000 and P10,000 class series of which "Pride Africa", "Pride Ango-la", operated by Pride International and Glomar C.R. Luigs" and "Glomar Jack Ryan", operated by GlobalSan-taFe, are derived. The design process of these vessels in combination with the current market requirements and latest drilling tech-nology developments, were triggers to adopt a design phi-losophy targeting more effective and efficient vessels to reduce required day rates, making operations more benefi-cial for all parties involved. Main design objective is to design on actual desired func-tionality, sizing the vessel for the intended purpose, whilst

still being able to adapt to new developments. The philos-ophy can be best characterized as:

1. Functional requirements and design criteria determine dimensions, arrangements and capacities.

2. Functionality based engineering leads to in-creased efficiency, smaller rigs and asso-ciated costs, better motional characteristics and associated uptime.

3. Fit-for-purpose, efficient and cost effective designs.

4. Increased efficiency leads to improved sus-tainability.

This philosophy was fully recognized by Ocean Riser Sys-tems and a combined effort has resulted in a PRD12,000 concept adapted to ORS drilling system, to be a trend breaker in the 6th generation. Ocean Riser Systems Drilling Technology. Background.

Ocean Riser Systems AS (ORS) was established in 2002, following a period of intensive technology devel-opment during the previous 7 years by the companys in-itiators. The basis for the start up was the recognition of some basic facts about the oil industry and the way it op-erates today, coupled with several developments taking place at the time. One of these basic facts is that the technology for control-ling pressure in the underground has remained unchanged since the start of oil well drilling more than 100 years ago. Secondly, the equipment for transferring drilling fluid from the well to the drilling rig and the pressure control equipment had remained essentially the same for the past 37 years. Thirdly, underground pressure and the way it is controlled, is the main driver and the determining factor for how we operate, how long it will take to construct a well, how much it will cost, how much it will produce and how big a risk we are taking in the process. Exploration drilling and subsea production is moving out to deeper and deeper waters. By keeping the basic riser technology and well control principles unchanged, the result is an ever increasing MODU size and increased top-side capacities of rigs being able to operate and drill wells under these conditions. Hence, operators are facing ever increasing well costs and increasing CAPEX in subsea field developments. More than 50 % of the total CAPEX in subsea field developments comes as a result of the cost of wells. Further still, the results from large subsea field developments that were started in the beginning of 90s, now shows that these developments are lagging far behind offshore fields developed with fixed platforms in reservoir recovery. As a result of a the new riser technology and pressure con-trol principles developed by ORS, coupled with a new and exciting technology development within the Norwegian energy cluster in subsea pumping and multiphase transient flow simulations, a brand new way of controlling and managing underground pressure arose. ORS has coupled these technologies together in order to improve the way

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the industry will drill wells and produce hydrocarbons in deeper waters. This new pressure management technology comes in un-der the terminology called Managed Pressure Drilling (MPD). The ORS patented riser and pressure management technology will allow for MPD to be carried out safely in the sub sea market segment and is particularly tailored for water depths of 250 m and deeper. The technology will not only control underground pressure but also effectively manage the pressure inside the well being drilled to always be optimum. With todays traditional technology, this is not always achievable. Secondly, the MPD technology can be used in all drilling segments; exploration drilling, development drilling, well completion, well intervention and workovers and in all sections, from tophole drilling through to the reservoir. Thirdly, the technology will facilitate the use of smaller vessels with equivalent 3rd geneartion rig capacity, to drill wells in ultra deep waters without significant reduction in hole size through the reservoir zone. Managed Pressure Drilling.

The drilling industry has been fighting pressure since its inception, and the basic approach has been un-changed for decades. Hydrostatic pressure is the prime means of bottom hole pressure control in conventional drilling, where the pressure in the formations is kept under control by the hydrostatic pressure generated by the col-umn of drilling fluid in the borehole. The mud weight (density) of the drilling fluid is adjusted depending on formation pressure and well condition so that the well is in an overbalanced condition when no drilling fluid circula-tion takes place. Changing the bottom-hole pressure is, however, a time consuming and costly process, which re-quires adding / subtracting chemicals and weighting mate-rials to the whole drilling mud volume. The core of ORSs technology is to enable continuous dynamic control of the pressure in the borehole throughout the drilling operation. The technology with the Low Riser Return System (LRRS) relies on a high pressure drilling riser with a BOP system split between subsea and surface. At a pre-determined level between surface and sea bed, a specially designed instrumented riser section is placed so that the return fluids can be drawn from the main drilling riser into a separate return line where a submerged drilling fluid pump (mud lift) system is located at approximately the same depth as the outlet from the drilling riser. In the mud lift return system connecting the submerged pump with the rig, there is another line parallel to the return line which is coupled to the mud suction line for filling and fluid level control within the drilling riser. Referemce is made to the schematic in Figure 8 for the main compo-nents. A multiphase real-time flow simulator for calculating the dynamic annular pressure is connected to the mudlift pump power distribution system. This particular software will calculate the downhole dynamic pressures and send signals to the subsea pump power distribution system, which again will regulate the level inside the drilling riser. The subsea pump system will regulate the bottom hole

annular pressure to the desired level by controlling the fluid level inside the riser. By using the system in this fa-shion, the bottom hole pressures can be adjusted conti-nuously so that it is always optimal for the drilling process. By being able to continuously regulate and con-trol the bottom hole pressure, the results will be;

1. Faster drilling. 2. Ability to drill longer between each casing. 3. Less downtime (As much as 45 % of all non

productive time in operations is related to inadequate pressure management).[3]

4. Reduced consumption by drilling a slender well.

5. Improved well safety. By being able to continuously manage the bottom hole pressure and by being able to compensate for all dynamic pressure effects from operations, an additional benefit is that wells can be drilled close to balance with the pore pressure in the reservoir section. In fact safe underba-lanced drilling may be undertaken while still being able to keep a positive riser margin. This may lead to less forma-tion damage and consequently increases the productivity of the wells and the reservoir. Also new and improved completion procedures can be performed. In addition the same riser as used for drilling can be used for performing well interventions, giving rise to more cost effective inter-ventions. The combined effects of this technology will dramatically improve NPV of subsea development projects by;

Reduced CAPEX through reduced drilling cost.

Improved recovery through improved drai-nage & intervention methods.

Increased safety through more barriers and lower surface pressure.

One important factor with the ORS method is that the sys-tem is a single gradient technology. Being able to drill with a heavier than conventional drilling mud and being able to transfer the pressure down into the well (closer to the source) will in physical terms be the most important factor for being able to drill longer sections. Reference is made to figure 3. This in combination with being able to compensate for the annular friction pressure (ECD), is different from most other MPD methods which rely on having a lighter than conventional drilling mud and then apply a pressure on top.[4] Reverse Engineering- Arriving at Subsea and MODU Specifications.

Being able to drill longer sections between each casing point is very important and this gives rise to a host of advantages in relation to the topside requirements on the MODU. In fact what has been done in this project is to ask a simple question such as; what hole size will be needed through the reservoir section of interest and then perform reverse engineering to find out what requirements are needed in the subsea package and on the topside drill-ing installation. Requiring a minimum hole size of 6, will give a slim well

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profile which can be drilled within a surface casing size of 11 3/4, without requiring expandable technology in most cases for as long as the MPD technology is applied. Solid expandable technology can be applied as contingency. For as long as the surface casing is designed to be able to withstand the maximum expected surface pressure, all subsequent casings can be run as liners. This will reduce the time to run casings and save time since no casing han-gers are needed in the wellhead. Hence a very simple wellhead can be used. An 11 surface casing can be run in conjunction with an 11 wellhead and an 11 Subsea BOP. The MODU can then carry an 11 ID riser. The 11 riser is high pres-sure and a 13 subsurface BOP is installed near surface. Hence there are no needs for long kill and choke lines with this system. Above the upper BOP a conventional drilling riser slip joint and riser tension system will be applied. For underbalanced intervention work in live wells with wireline or coiled tubing (CT) operations, a high pressure extension will be run through the low pressure slip joint and anchored in the top of the upper subsurface BOP. This high pressure joint will be supported in the upper end by the rigs main hoisting and compensation system or by a constant tension winch on the rig floor, creating a high pressure conduit from the well up to the rig floor on the MODU. Wireline or CT BOPs can then be rigged up on the drillfloor. All activities can be performed without hav-ing to disconnect the main riser or occupying the subsea BOP with a concentric workover riser, as in conventional operations. Being able to drill a slim well in deep water will allow for less space and weight requirements for drilling equipment and consumables on the MODU. (Fig. 2) In fact it is esti-mated that the water depth capacity for any given drilling rig can be doubled as a rule of thumb. However this does not remove the challenge with regards to station keeping in deep waters with conventionally moored MODUs. Cost saving aspects Time and Consumables.

The main cost driver, as spread rates are spiraling upwards, is time. Reducing the drilling and completion time is the most important factor in cost reduction. Reduc-ing flat-spots, naturally caused by casing points and non-productive time and extraordinary downtime, is of prime concern. The main driver for time reduction is the ability to stay on bottom and making hole faster for a longer pe-riod of the time, without creating a later increased risk for trouble-time or downtime. This can hardly be done with-out some form of new approach to pressure control and

pressure management of downhole pressures. Dual activity and dual derrick rigs can support the higher dayrates due to the improved efficiency in operations in conventional drilling. With the ORIBIS PRD12,000 drill ship design, both cost reduction in dayrate and improved efficiency in the hole making process have been targeted. The main driver for time reduction in drilling is the ability to drill longer sections and leave out casing strings.(Fig. 4) Casing installation and cementing is the most time con-suming activity in hole construction next to drilling the hole itself. Being able to drill longer sections is hence a huge time saver. It will also have the potential to save trips, circulation time, trouble-time and potential down-time with casing operations. The ORS MPD principle has been investigated on a number of different locations and geo pressured areas around the world and compared to conventional pressure control. Depending on the water depth and the operating pressure envelope, considerable time savings can be expected. Figure 5 provides an indica-tive number on the potential well cost saving for different water depths in 2 different areas (Norway (NCS) and Gulf of Mexico (GOM) compared to wells drilled conventional-ly with a 5th or 6th generation rig. Drilling slim wells through a slim high pressure riser as for the ORIBIS PRD12,000 drillship, will substantially reduce the amount of consumables required. Although the reduction in both the amount of steel casing, mud, cement and chemicals is considerable in relative cost terms, the effect of a reduced environmental impact and footprint of the entire operation, might be as important. The estimated reduction in consumables for a typical slim deepwater well in the Gulf of Mexico, compared to a conventionally drilled well on the same location, given the same esti-mated pore and formation fracture pressure is shown in Figure 6. PRD12,000.

The PRD12,000 drill ship concept was developed in 2003 to break the upward sizing trend by making use of unconventional drilling techniques for floating units, with the main objective to reduce the cost per well. The basic benefit of using surface equipment with pressurized riser is a vessel size reduction on main dimensions and dis-placement, enabled by the savings of equipment weight and decrease of required drilling loads and tank volumes, such as active and passive mud pits, bulk pods, base oil and drill water, as indicated in the comparison table (table 01).

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Table 01 - 10,000ft water depth drill ship design loads

Pressurized Riser & Surface BOP Drilling Conventional LP Marine Drilling Riser Mode Typical design load comparison for 10,000 Water depth Slip joint 20 t Slip joint 25 t SBOP stack (13"3/8) 68 t Marine Drilling Riser 3,000 t Slim line Riser 1350 t LMRP 50 t SS BOP 130 t BOP stack (18"3/4) 250 t Wellhead connector 30 t Wellhead connector 50 t Total 1598 t Total 3,375 t Indicative substructure loads comparison for 10,000-12,000 Water depth Hook/ rotary load 500 -750 t Hook/rotary load 750-1,000 t Required Riser Tension 750 t Required Riser Tension 1,250 t Setback 500-750 t Setback 750-1,250t Total 1,750-2,100

t Total 2,750-3,500 t

Indicative tank volume comparison for 10,000-12,000 Water depth Active and passive mud 1,000 m3 Active and passive mud 2,000 m3 Bulk pod (cement, barite, bentonite) 500 m3 Bulk pod (cement, barite, bentonite) 800 m3 Drill water 2,000 m3 Drill water 3,000 m3 Base oil 300 m3 Base oil 500 m3 Brine 400 m3 Brine 500 m3

The capacities required for deep water drilling with pres-surized riser techniques reduces the requirements for the weights and volumes for the rig with approximately 50%. This enables the vessel size to be reduced. However these capabilities will still enable the smaller rig to accommo-date a conventional subsea system to water depths of 5,000.

ORIBIS PRD12,000 CONCEPT design.

The ORIBIS PRD12,000 derivative is characte-rized as a very compact design, with all vessel and drilling systems highly integrated in the hull to decrease size as much as possible, fully in accordance with the GustoMSC drill ship design philosophy and Ocean Riser Systems tar-get for cost per well saving. An impression for the vessel is included in Fig. 7.

General description.

General layout of the vessel is based on the PRD12,000 concept, adapted to the special requirements for the ORS MPD system.The hull accommodates the en-gine rooms including auxiliaries and main switchgear at the aft, the accommodation deckhouse for 136 persons is located forward on the vessel, including helicopter recep-tion facilities and associated safety equipment. The ac-commodation support facilities and pump rooms will be located in the hull below the accommodation deck house. Typical feature of the GustoMSC drill ship design is the covered corridor from accommodation to engine room below main deck on both SB and PS, providing a fully protected passage and easy accessible cable and pipe trunk from aft to fore. The mid ship hull part will be reserved for a relatively large drilling moonpool of 16.9 x 10.6 m, with all drilling support utilities in the hull spaces adjacent to the moon-pool. Bulk pod rooms and support air will be allocated

alongside the moonpool, brine and mud pits and mud pump room forward of the moonpool and aft of the moon-pool the electrical rooms, workshops, compressors and HPU rooms. At the aft of the moonpool a cellar deck for BOP handling and a double skid cart arrangement will be provided. (Fig 9) Riser storage and drill pipe storage will be provided on the aft deck area, casing and liner storage will be on main deck forward and in a pipe hold. At the center, a substruc-ture with a split level drill floor will be provided. The drill floor essential equipment, such as drillers cabin, iron roughneck, rackers and standpipes, will be located at an elevation of 30.5m above base. Equipment not strictly required on the drill floor will be allocated on the utility floor level at an elevation of 23.6m above base, to improve stability performance. Utility floor equipment comprises C&K manifold, drawworks, tool pushers office, LER and drill line reel. MPD system.

The vessel is designed for dual capability. It is able to be fitted with a conventional 18 subsea BOP, 15k with a 21 LP riser system to reach water depths of 5,000, but is especially adapted for the Ocean Riser Split BOP high pressure riser system being able to reach to 12,000 water depth environments. The MPD system will comprise the following equipment for well control (Fig. 8):

Wellhead and wellhead connector 15,000 psi WP subsea BOP with 4 ram cavi-

ties RDP Riser disconnect package MPD interface joint and connection hose 90 HP riser 11 ID 10,000 psi WP

(130 joints)

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10,000 psi WP subsurface BOP 21: riser joint and LP slip joint 55 stroke MPD pump MPD riser MPD umbilical

The HP riser, subsea and subsurface BOP will be handled and run as usual including the riser interface joint. The differentiating aspect of the ORS system is the MPD pump which is deployed separately, requiring adjustments im-pacting the design of the ship. For efficient and safe han-dling of the MPD system a separate MPD pump running moonpool is allocated in the forward part of the ship and part of the main deck is allocated as a dedicated MPD area. The equipment comprising a storage area for the hard piped dual bore riser used for running the pump, the asso-ciated handling system, a skidding area and a horizontal to vertical handling arrangement for the MPD pump (shown in fig 10 to 12). The skidding area may also be used for X-mas tree storage when extending the functionality of the rig. A separate hoisting arrangement will be supplied for running the subsea mud pump system on a dual bore riser to a maximum of approximately 600 m below sea level. ORIBIS PRD12,000 in perspective of 6th generation.

The value of the design is best assessed when compared with a typical 6th generation rig. The 6th gener-ation rig is characterized as a tanker based large dual der-rick drill ship, upgradeable to crude storage functionality versus the fit-for-purpose ORIBIS PRD12,000.

Vessel characteristics.

The character of the concept is immediately iden-tified in the principal dimensions demonstrating major differences. However the moonpool size of the ORIBIS PRD12,000 design is relatively large, to enable completion activities requiring X-trees to be run from the ship. Other differences are reflected in total complement of per-sonnel, single derrick requiring less people and power. Furthermore the smaller size enables less power to be in-stalled on both the power generation side and the dynamic positioning thruster system. The difference in size is indi-cated in Fig.13, where the ORIBIS PRD12,000 and a typi-cal tanker based 5th generation are depicted; the 5th genera-tion having the same dimensions as the latest 6th genera-tion developments. In figure 14 and 15 vessel characteris-tics are compared between ORIBIS PRD12,000 and a typ-ical 6th generation rig.

Table 02 - vessel characteristics

Name ORIBIS-ONE

Typical 6th generation

Type Drillship Dual Drillship Length [m] 156.0 228.0 Breadth [m] 29.9 42.0 Depth [m] 15.6 19.0 Toperational [m] 9.0 12.0 Displacement operational [t] 35,000 96,000 Moonpool length [m] 16.9 25.6 Moonpool width [m] 10.4 12.5 Accommodation [POB] 136 180 Power installed [MW] 28.8 42.0 Thruster power [MW] 24.0 33.0 Transit Speed [kn] 12.0-14.0 10.0-12.0

Fuel [m3] 3,300 6,500 Drilling capability.

Evidently the drilling capabilities of the designs are different, since a single derrick rig is being compared with a dual derrick rig. Still the drilling capability can be expressed as the ability to drill, intervene or complete a well, characterized by formation, environment, water depth and drilling depth. Comparing the listed drilling capability the rigs are capable of handling the same type and class of wells. The 6th generation targets increasing efficiency per well by offline capability, where the ORIBIS PRD12,000 increases efficiency by reducing the cost of the vessel and enhancing the drilling efficiency by the MPD technology. The drilling capability comparison is depicted in the figures 16 and 17.

Table 03 - drilling capability

The differences in riser tension should be read carefully. Due to the riser dimensions the ORIBIS PRD12,000 is able to reach larger water depth with less tension. The

ORIBIS-ONE

Typical 6th generation

Waterdepth [ft] 12,000 10,000 Drilling Depth [ft] 30,000 34,252 Derrick/Hook [kips] 1,500 3,200 Riser tension [kips] 1,800 2,500 Setback [kips] 1,100 1,750 Bulk pod storage [bbl] 3,500 5,000 Mud pit capacity [bbl] 6,300 11,300 Brine [bbl] 3,750 3,150 Drilling Water [bbl] 13,200 25,200 Potable Water [bbl] 10,000 12,500 Base Oil [bbl] 2,100 3,150

Crude Oil [bbl] 0 95,000

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smaller riser dimension also enables the mud volume re-duction and associated support consumables as drill water, brine and bulk, so the drilling capabilities are actually comparable.

Another large difference is that the future crude storage option of the 6th generation is not adopted in the ORIBIS PRD12,000 concept. Dropping the requirement of storage enables a large size reduction and allows an integrated design. Having major drilling equipment accommodated in the hull allows for small beam vessel, improving the acce-lerations characteristics due to roll motions, which may become more severe with large beam vessel as the typical 6th generation vessel. On the positive side the stability of the vessel is less critical for large beam designs, so the beam reduction is taken into careful consideration during the design and needs to be monitored during operation of the ORIBIS PRD12,000 concept. Vessel performance.

To identify the impact of the size reduction of the vessel four performance indicators are presented:

Sustainability impact on natural resources Dynamic Positioning performance Speed and resistance Sustainability Fuel oil consumption

From these performance indicators the impact of fit-to-purpose design versus the tanker based design is clearly demonstrated. Sustainability impact on natural resources.

The impact on natural resources can be indicated by the amount of hull steel required for the vessel to be built. This is indicative for the amount of base material required, but also is indicative for the power and equip-ment involved for construction of the rigs. Basic hull steel estimates for the vessels indicates that the 6th generation vessel required more than 2.5x as much steel and associated power, than is required for the ORIBIS PRD12,000 design (Fig. 18). This excludes the associated drilling equipment and vessel systems. Another effect for this reduced throughput of material might be a shortened delivery time of the rig, or at least the hull. Dynamic Positioning performance.

The dynamic positioning is performance of the typical 6th generation rig as is compared to the ORIBIS PRD12,000 design. These capabilities are calculated with exactly the same assumptions and software. It is demon-strated in figure 20 that the ORIBIS PRD12,000 footprint according DPVOA relations exceeds the 6th generation, in both intact conditions OR the combined single thruster failure envelope. The difference can be explained by the reduced environ-mental forces on the ship, due to the size reduction. It should be noted that the ORIBIS PRD12,000 thrusters are relatively large to increase the operational envelope in the Gulf of Mexico loop current events, which may result in heavy beam on conditions. Speed and resistance.

With the upwards spiraling day rates quick mobi-

lization and de-mobilization in between locations and op-erations will save considerable money for the end user. Now , even transit time to dry dock every five years might enter into the equation. The resistance graph in Figure 21 show the added resis-tance for the moonpool, without taken any resistance miti-gation devices in to account. This means that the speed of both designs may be enhanced with 0.5 to 1.5 knots, when applying such devices. For drill ships, several propulsion concepts can be applied depending on the thruster arrangement. In the industry most options available have been used, ranging from the use of two stern thrusters, to deploying all thrusters below keel level and use them to increase speed. The latter will demand relative large additional power almost doubled for 1 to 2 knots speed increase. In this figure two (2) or three (3) aft thrusters is used as propulsion concept. Sustainability Fuel oil consumption.

Second indicator with respect to sustainability is fuel consumption. The fuel consumption rate is based on drilling operations in DP mode for two different environ-mental conditions. For this comparison 70% of the time drilling is in a 2.0 meter wave height environment with associated wind speed of 10 m/s and current speed of 1.0 m/s, all colinear. The remaining 30% of the time is in 4.0m significant waves, with 20 m/s wind and 1.5 m/s current. The heading angles are varied between 0 and 30 degrees. The comparison (Fig. 19) shows that there will be almost 50% fuel saving for the ORIBIS PRD12,000 con-cept compared to a larger 6th generation drill ship. In tran-sit the difference is smaller, however the attainable transit speed is higher for the ORIBIS PRD12,000 design. Cost comparison.

The performance indicators can be translated into lower investment costs for the rigs or lower operational costs. However cost of new rigs is highly influenced by the general market situation both for the shipyard industry and the general drilling equipment supply market at large For example in the drilling equipment market, smaller and lighter equipment, such as derricks and drilling packages, risers, BOPs, control systems, etc, might not translate into lower cost. Engineering costs will also be higher due to new designs. Still it can be concluded that the ORIBIS PRD12,000 rig will be less costly than the typical 6th gen-eration competitor as indicatively indicated in table 04. However all things are not equal. There are dual derrick rigs, dual activity rigs, single activity rigs and now MPD rigs. For the end customer though, the most important is the final cost and the performance and quality of the well. Day rate is important, but efficiency is more important. ORIBIS PRD12,000 being a single activity MPD rig will be less costly in dayrate, but considerably more efficient by the MPD system in to the increase in efficiency by the dual derrick systems, resulting in lower cost per well for the end user, as demonstrated in Figure 22.

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Table 04 - order of magnitude cost overview

Conclusions In this paper it has been identified that reversing the trend in the current spiraling growth of drilling rigs is made possible using the improved MPD drilling techniques, taking full advantage of the reduced drilling loads, when applying it on the compact drill ship design in the PRD12,000 concept. Making use of the decreased size drill ship concept with enhanced drilling technology enables the contractor to drill deepwater wells which conventionally requires a typical 6th generation drill ship. In this paper it is shown that the ORIBIS PRD12,000 concept will have improved perfor-mance indicators; sustainability impact on natural re-sources and fuel oil consumption, DP and speed, all at lower costs. However it should be noted that a 6th genera-tion rig equipped with a dual derrick, will be more effi-cient in drilling if the MPD system is not included. Never-theless the difference in cost is expected to be considera-ble, which makes the ORIBIS PRD12,000 concept a com-

petitive alternative to the existing and future 6th generation fleet. References

[1] DOT2007 ID 137 GustoMSC drill ship designs increasing efficiency in deep water operations Author: Sjoerd Hendriks GustoMSC Co-authors: Jaap-Harm Westhuis, Martijn Ooijen GustoMSC

[2] Offshore Magazine article: Downsized drill ship allows operations in wider depth range November 2006 PenWell Corporation Authors: H. Tiebout & S.M. Hendriks, Gusto BV

[3]Offshore Magazine article: Gulf of Mexico 'trouble time' creates major drilling expenses, January 2004 PennWell Corporation- Authors: James K. Dodson

[4] SPE/IADC 91633, Managed Pressure Drilling for Subsea Applications; Well Control Challenges in Deep Waters, Fossili, Brre, Ocean Riser Systems AS, Sangesland, Sigbjrn, Norwegian University of Science & Technology ,2004 SPE/IADC Underbalanced Technology Conference and Exhibition held in Houston, Texas, U.S.A., 1112 October 2004

[5] A Comparison of Subsea Drilling Methods, Paulsen Per Olav, Diploma theses 2006, Norwegian University of Science & Technology

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

110%

ORIBIS PRD12,000 Typical 6th generation

Newbuild price -high

Newbuild price -low

112388 9

Fig. 1

Riser Capacity

1 000

2 000

3 000

4 000

5 000

6 000

500 1 000 1 500 2 000 2 500 3 000 3 500 4 000

Riser Depth (m)

21 " Riser Capacity14" Riser Capacity

Capa

city Vol. Reduction

-63,2%

Fig. 2 showing a slim riser for 12000 having same capacity as a conventional riser for 4500

10 112388

Pressure vs Depth

0

2000

4000

6000

8000

10000

12000

14000

0 2000 4000 6000 8000 10000 12000

Pressure PSI

Verti

cal D

epth

Pore Pressure Formation Fracture Pressure

Conv.MPD w/surface Pressure

LRRS

Pressure vs Depth

0

2000

4000

6000

8000

10000

12000

14000

0 2000 4000 6000 8000 10000 12000

Pressure PSI

Verti

cal D

epth

Pore Pressure Formation Fracture Pressure

Conv.MPD w/surface Pressure

LRRS

Fig. 3 showing increased drilling length compared to conventional [4]

Time vs depth

0

2000

4000

6000

8000

10000

0 10 20 30 40 50 60 70 80

Days

mTV

D

ConventionalORIBIS

Fig. 4 - Drilling time vs depth : Conventional vs rig with LRRS (Deepwater GOM)

112388 11

ORIBIS Cost Savings Potential

0,00 %

10,00 %

20,00 %

30,00 %

40,00 %

50,00 %

NCS 1260 m WD GOM 2286 m WD

Fig. 5 - Well Cost Saving Potential with ORIBIS DS with reference to a typical 5th or 6th generation rig

Well cost - consumables -Deepwater GOM

-

1 000

2 000

3 000

4 000

5 000

6 000

7 000

8 000

9 000

10 000

Base Case LRRS

Cos

t in

1000

USD Casing

Well equipment and WH

Drill bits

Diesel

Mud

Cement

Fig. 6 - Cost of Consumables: Conventinal compared to slim well with LRRS

12 112388

Fig. 3

Fig. 4

Fig. 8

Fig. 9

Fig. 7

112388 13

Fig. 10

Fig. 12

Fig. 11

14 112388

Fig. 13

112388 15

Fig. 16 Fig. 17

0

5

10

15

20

25

30

35

40

45

Power installed [MW] Thruster power [MW] Transit Speed [kn]

Oribis 6th Gen

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

Waterdepth [ft] Drilling Depth [ft]

Oribis 6th gen

Fig. 14 Fig. 15

0

500

1,000

1,500

2,000

2,500

3,000

3,500

Derrick/Hook [kips] Riser tension [kips] Setback [kips]

Oribis 6th gen

0

5,000

10,000

15,000

20,000

25,000

30,000

Bulk pod storage[bbl]

Mud pit capacity[bbl]

Brine [bbl] Drilling Water[bbl]

Potable Water[bbl]

Base Oil [bbl]

Oribis 6th gen

typical 90-100k bbl optional crude storage for 6th gen

0

10,000

20,000

30,000

Hull steel [t]

Oribis 6th gen

0.0

20.0

40.0

60.0

80.0

100.0

Transit [t/day] DP drilling [t/day]

Oribis 6th gen

Fig. 18 Fig. 19

16 112388

Fig. 20 DP footprint comparison

Fig. 21 resistance comparison

Thrust/Resistance ComparisonORIBIS ONE vs TYPICAL 6th GENERATION

(no resistance mitigation devices in moonpool taken into account)

0

250

500

750

1,000

1,250

1,500

1,750

2,000

2,250

2,500

2,750

3,000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Ship speed [kn]

Res

ista

nce,

Thr

ust [

kN]

R_Oribis

T_Oribis (2x4MW)

T_Oribis (2x4+1x4MW)

R_6th gen typ

T_6th gen typ (2x5.5MW)

T_6th gen typ (3x5.5MW)

eq1

eq2

eq3

eq4

112388 17

Figure 22 - Well cost as a function of drilling time and rig rates [5]

Reduced Time vs. Reduced Rig Rates

25 %

50 %

75 %

100 %

125 %

150 %

25 % 50 % 75 % 100 % 125 % 150 %

Percentage of actual time (100 % =Conventional Single activity)

Perc

en

tag

e o

f act

ual

rig

rate

s (1

00

%=

5th

.gen

rig

, si

ng

le a

ctiv

ity) 60%

70%80%90%100%110%120%

Dual derrick

ORIBIS

% of total well costDual derrick & LRRS