bluuebunny/crossref_metadata_2025 huggingface dataset:
Concrete Hulls For Tension Leg Platforms
Authors: de Oliveira J. , Fjeld S.
Published: October 2008

This paper describes the main features of a concrete hull TLP concept developed for the Heidrun Field. The hydrodynamic response and the methods adopted to optimise the hull dimensions are first discussed, as well as the mooring system and the hull mechanical outfitting. The construction methods and possible transportation and installation scenarios are presented. The subjects of inspection, maintenance and repair are also briefly addressed. Finally the advantages of the concrete hull TLP concept are summarised, including it's adaptability to a large range of design requirement, its insensitivity to moderate design changes, and its low cost and short construction time. This paper shows how the concrete hull TLP can offer a very cost efficient solution for the development of deep water fields.

INTRODUCTION

The Tension Leg Platform (TLP) is a compliant offshore structure that offers great advantages for drilling and production operations, particularly in deep waters. The concept is now well known, given almost four years of successful operation of the Hutton TLP in the U.K. Sector of the North Sea. Efforts are now being made to improve the capabilities of such platforms, especially with regard to increased payload, more efficient methods of construction, simpler mooring systems and foundations. These efforts are leading to cost effective alternatives which will make the TLP concept a front runner for many offshore field developments. One such alternative is the concrete hull TLP, which is the subject of this paper.

By choosing concrete as the building material for the TLP hull it is possible to design the platform for topside loads of 50.000 t or more. Also, concrete offers many advantages, such as a relative insensitivity to fatigue and corrosion, minimum maintenance requirements and small loads on the mooring system and foundations. The construction period required for concrete is significantly shorter than for steel, and the associated costs are also expected to be lower. It is felt that the possibility of using concrete as a building material for the TLP hull brings a new dimension to the TLP concept, and makes it even more attractive in the development of large deep water offshore fields.

The present paper describes the main features of a concrete hull TLP conceptual design developed for the Heidrun Field, in the Haltenbanken area of the Norwegian sector of the North Sea. This concept has been adopted for the development of the Heidrun Field by Conoco Norway Inc. and its Co-licensees. A description of the concrete hull TLP is given, including the design basis and requirements, the platform dimensions and configuration, the hydrodynamic response, the hull structure, the mooring system, the mechanical outfitting, construction, transportation, installation and operation. Finally, the advantages of the concrete hull are discussed, and the most salient features of this concept are summarised.
Model Testing Of A Deepwater Salm/Tanker System
Authors: Watson G.D. , Koch S.P. , Watson M.J.
Published: October 2008

The paper describes the results of physical model tests undertaken to investigate the performance of a deepwater SALM/tanker system in a wind, wave and current environment. The system tested is an element of the Esso Deepwater Integrated Production System (EDIPS), for which a conceptual design was completed in 1987 for Esso Exploration and Production UK Limited.

The testing program required development of several novel transducers which are described in the paper and necessitated hydroe1astic modelling of the SALM lower riser to ensure that accurate vibration response to wave and flow excitation was obtained. Tests were undertaken in a variety of conditions which included multidirectional waves and oblique wind directions. The test results demonstrate the increased loading and motions caused when the environmental loading is not collinear. The vibration response of the lower riser and the effect of an inertia skirt on the performance of the double articulated SALM are also described in the paper.

INTRODUCTION

An extensive matrix of wave tank model tests were carried out at the British Maritime Technology (BMT) on a model of a deepwater SALM/Tanker system. The work was funded jointly by Esso Exploration and Production UK Limited and the UK Department of Trade and Industry Marine Technology Committee, and was done under the technical stewardship and coordination of Esso's research affiliate, Exxon Production Research Company.

The model tests were conducted with two primary objectives:To act as a comparison for BMT's time domain computer simulation program BMTSPM.To study the dynamic behavior of the SALM/tanker system, which is an element of the Esso Deepwater Integrated Production System (EDIPS) (Reference 1).

The SALM system (Figure 1) consists of a buoy moored to the seabed by a single, tensioned riser. The system was designed to operate in a water depth of 610 meters and moor a storage tanker of approximately 250,000 deadweight tonnes capacity. The riser was pin-jointed at both the seabed and the connection with the lower buoy. A removable inertia skirt was fitted to the lower buoy to increase the local added mass and reduce the motions at the mid-water universal joint. The buoy was connected to the tanker by a rigid, pivoted yoke.

The SALM buoy, yoke, and tanker models were fabricated conventionally as rigid elements, and were fitted with lead weights to achieve the desired weight, center of gravity and radii of gyration. A flexible model of the riser was designed and built to have the proper scaled bending stiffness. This was a principal challenge of the program, and was done so that the riser's vibration response over the frequency range of predominant wave energy could be measured. Unlike the approach usually taken to model test shallow water SALM systems, the riser cannot be considered a rigid element in deep water systems.
Operational Problems of Offshore Oil Loading and Possible Solutions To Overcome the Weather Limitations
Authors: Sterzenbach M.
Published: October 2008

Offshore loading systems have often shown unsufficient reliability and therefore often influenced the regularity of oil transportation from offshore production facilities to shore.

Most of the unregu1arities were caused by environmental conditions and handling difficulties.

This paper reflects on the problems with loading systems in the past, shows future development tendencies and describes a loading system which helps to avoid the problems which occured so far.

The author was in charge for the mechanical and operational development of the subsea oil loading system - SOLS.

INTRODUCTION

The production and transportation of oil and gas is done in a century old technology and does not cause problems so long the field is onshore. When the oil production started offshore the development of the necessary technology to achieve this production became a real challenge for the engineers. The environment and the waterdepth generated the tallest buildings on the world - the production platforms and the most expensive oil and gas transportation systems: either pipelines or loading systems for tanker transportation.

For offshore installations, the greatest design influence is not defined by the production quantity of oil and gas, but by the environment.

Therefore the greatest attention has to be paid to the optimization of the system ability to withstand the environmental forces.

This is normally done by strengthening the design or optimization of e.g. motion behavior or decksload. In the following the problems of oil loading systems are discussed and a system is presented which is not affected by the harsh environment conditions.

The presented new oil loading system was developed to overcome the environmental and operational problems. In order to achieve this requirement a total change in design compared to present loading systems was necessary.

PRESENT LOADING SYSTEMS

The loading systems used today are:

(Available in full paper)

some other designs appeared on the scene like flexible steel risers as e.g .. Monopi1e (Fig. 5) anchored floating towers as recently proposed for Shell's Norwegian Draugen field, bow or center turret mooring systems which are mainly used for fixed mooring of ship based production systems. In the latter case the transportation tanker connects to the stern of the production ship.

Each system offers particular advantages and also disadvantages as explained lateron.

All concepts and realized systems have a surface mooring line connection to the tanker and a free hanging or floating hose connected to a tanker manifold. While the floating hoses of the SBMs are connected to the midship manifold, the ALPs, the realised UKOLS and the SALM use a hose connection to an additional bow manifold at the tanker.

The moored tanker weathervanes around the loading system.

The only concepts which do not use a surface connection method are SUBLOAD (Fig. 6) and SOLS (Fig. 7). These systems use a subsea connection method comparable to drilling riser connections.
Scour From Cyclic Lateral Loading of Piles
Authors: Reese L.C. , Wang S.T. , Long J.H.
Published: October 2008

Two types of scour can be identified at piles supporting offshore structures:erosion of the sea bottom (sea-bottom scour) at obstructions due to oscillatory waves and unidirectional currents, andthe loss of soil around a pile due to the cyclic deflection of the pile under wave forces. The second type (pile scour) is associated with cohesive soils and is the subject of this study.

Observations during onshore testing have revealed that the loss of lateral capacity of a pile in cohesive soils is due principally to the creation of a gap at the pile-soil interface and to the subsequent ejection of water from the gap at the space opens and closes during the cyclic loading.

The paper describes the phenomenon of pile scour, presents the details of a laboratory test to investigate the scour potential of various soils, discusses the significant findings of a research study, and indicates the influence of pile scour on the design of laterally loaded piles for offshore structures.

INTRODUCTION

A 24-in (610 mm) 0.D. pipe pile was driven into overconsolidated clay at a site near Manor, Texas and tested under static- and cyclic-lateral loading (1). The test was conducted in a shallow pit and water a few inches deep was kept in the pit at all times. The following statement is abstracted from the report on the, testing program.

"During cyclic loading, considerable scouring action was observed around the pile. The cyclic loading caused a pumping action in the water in the gap between the pile and the soil. This pumping action eroded the soil and widened the gap between the pile and soil; a hole to the side and slightly behind the pile developed during cyclic loading; the hole at the side was approximately 4 in. (100 mm) in diameter and 2 ft (600 mm) deep."

A test of a 3 by 3 group of piles, each 10.75 in. (273 mm) in diameter and on a center-to-center spacing of 3 diameters, was conducted at a site on the campus of the University of Houston (2). The surface soils were overconsolidated clays that were jointed and slickensided. The investigators reported that grayish silty clay, existing below a depth of 4 ft (1.2 m), was pumped up to the ground during cyclic loading.

The objectives of the study described herein were to present a qualitative description of the mechanism of scour or soil erosion at the interface of pile and clay (pile scour) and to provide a means of identifying clays that are susceptible to such scour. The mechanism of scour at the pile-soil interface is described in general terms, and details are presented of a laboratory test for investigating the scour potential of various soils. In the laboratory tests, soil samples with different characteristics were selected and tested. Studies (4) were made of natural soils from the Sabine, Texas site (5), the Manor, Texas site (1), and from a North Sea site.
Suction Anchors as an Anchoring System for Floating ,Offshore Constructions
Authors: Larsen P.
Published: October 2008

The paper describes the result of model tests carried out with circular-cylindrical suction anchors. The purpose 6f the tests is to examine the mechanical behavior of soil and structure during installation and to determine the horizontal pulling capacity of the anchor at oscillating load compared to the pulling capacity at static load. The test results confirm the efficiency of the down suction method for installation and demonstrate that the horizontal ultimate pulling capacity of the anchor for fine-grained soils depends on the variation of the load with time.

INTRODUCTION

During the last decade the concept of using differential water pressure as driving force when structures are to penetrate the seabottom has been increasingly applied due to the increase in offshore activities. The method has been applied in the Danish part of the North Sea for anchor structures at the "Gormn" field (Senpere 1982) and recently in the Norwegian part for concrete skirt penetration tests on a large scale at Gullfaks (Tjelta 1986).

A suction anchor will often be constructed as a circular-cylindrical pile with a small length-to-diameter ratio. The ultimate resistance of a rigid pile against transversal static forces may be calculated by means of a method proposed by J. Brinch Hansen (1961). The calculations are based on the principle that the pile rotates as a rigid body around a point approximately 0.2× pile length above the pile tip as. indicated in figure 1.(Equation available in full paper)

In order to evaluate the test results, the theoretical pulling capacities calculated on the basis of the above calculation methods developed by J. Brinch Hansen and B. Broms are shown in figure 7.

In most cases only static load tests are performed with the anchor after installation, even though the load may be cyclic.

With the aim of comparing the horizontal capacity of the suction anchor at static load to the capacity at cyclic load a series of model tests with circular- cylindrical anchors in sand and clay has been conducted at the Danish Geotechnical Institute.

MODEL TESTS

A total of 15 model tests were performed, 11 of which were in sand. Of the 4 remaining tests 2 were carried out in clay and 2 in kaolin. A detailed description of the tests is given by P. Larsen (1987).
Behaviour of Embedded Mooring Chains in Clay During Chain Tensioning
Authors: Dutta A. , Degenkamp G.
Published: October 2008

With the help of experimental results, this paper first describes the behavior of embedded mooring chains connected to a buried anchor point. The tests were carried out on three different sizes of chain in two clays with different undrained shear strengths. Subsequently, the effect of changing the effective chain widths (for calculating soil resistances) on the chain forces at the anchor point has been discussed with certain analytical results. The studies are believed to be useful to the practicing engineers.

INTRODUCTION

Over a few decades, the anchor pile-chain system is being widely used with the single point mooring (SPM) systems of CALM-buoy type. In addition, as the offshore activities are moving towards deeper sites having soft soil, it is inevitable that the anchor pile-chain system will find wider application in connection with the mooring system of floating platforms and articulated structures like Guyed Towers. Hence, it is understood that the present topic is of relevance to the design practices of the mooring system with buried anchoring arrangement.

The connection point between the mooring chain and the anchor pile, which is commonly known as "pile lug", is generally positioned a certain distance below the seabed level. The basic season behind such a design is to economise the anchor pile design, utilizing the following two important factors:Embedded chain experiences a considerable amount of soil resistances which in turn, reduces the forces at the pile lug.Embedded pile lug minimizes the bending stress level in the pile section.

The optimum design of the pile lug location is however a critical issue; and this is so due to the pull-out and pile driving considerations. These two considerations can well be satisfied if the pile lug is positioned near the seabed level. On the contrary, the economy in pile design is achieved if the pile lug is located around the mid-height of the pile. Therefore certain trial and error approach is adopted in practice to obtain the most suitable lug depth, which may not essentially be an absolute optimum solution.

The analysis and design of an anchor pilemooring chain system involves the analysis of a part of the mooring chain (referred here as embedded chain) considering all probable soil-chain interactions. Basically, during the initial chain tensioning operation, the embedded chain length (which indeed varies with the line tension) starts cutting the soil medium deeper and moves away from the anchor pile. During this chain movement inside soil two types of soil resistance are developed. These are :resistance against cutting or bearing resistance, andresistance against sliding or sliding resistance.

These resistive forces from the soil medium can be idealized as normal and tangential distributed forces along the embedded chain length, and can be expressed in terms of undrained shear strength of soil (Su) as discussed by several authors (1 – 8).
Computation of Nodule Abundance From Seabed Photos
Authors: Sharma R.
Published: October 2008

Correlation between water depth, nodule coverage, abundance from seabed photos-and grabs and the relative abundance has been studied in different seabed settings .based upon thickness of sediment water interface boundary' (SWIB)I layer and extent of nodule burial at different locations. Whereas, nodule coverage and Abundance have an inverse relation with thickness of SWIB layer (due to nodule burial)l, there is a good correlation (? .75) between nodule abundance in photo -and grab. Relationships between actual nodule population and -variable burial under the associated sediments have been established and mathematical formulae worked out to compute nodule abundance from seabed photos in different environmental settings.

INTRODUCTION

Nodules are known to be buried to varying extents under the uppermost uncompacted sediment on the seabed or the Sediment-Water Interface - Boundary (SWIB)1 layer (Cronan and Tooms, 19671; Sorem and others, -1979), leading to an underestimation of nodule abundance from seabed photos. (Frazer and others, 1978, Bastein-Thiry, 19791 Anonymous, 1982). Studies on comparison of nodule abundance from grabs and photos have emphasized the need for a correction factor to be applied to photo estimates to account for buried nodules (Fewkes and others, 1979; Felix, 198?). However, no single correction factor can be applied to all estimates (Felix, 198?), as the nodule burial also depends upon the varying thickness of SWIB layer at each location (Sharma, In press).

Several methods have been proposed for estimating nodule abundance from photos (Bastein Thiry, 1979; Fewkes and -others, 1979; Handa and, TsuIusaki 1981) and have attained an accuracy of 5?-8f? -% with respecit to actual nodule abundance. This study aims at quantifying the burial of nodules and thickness of SWIB layer in-different seabed settings -which can be used to estimate nodule abundance accurately, so as to make seabed photography an independent and reliable tool for nodule exploration.

METHODS

Seabed photographs at 285 location, were taken, using cameras attached to freefall grabs, 1-1.5 m above the seabed, Nodule (C) was estimated in percent by superimposing a graph sheet and counting the number of squares falling on nodules with respect to area of the photograph.

(Equation available in full paper)
Metallic Sealing Technology in Downhole Completion Equipment
Authors: Blizzard W.A.
Published: October 2008

Metallic seal systems are relatively new to downhole completion equipment. Their incorporation into downhole products represents a trend toward higher technology in extreme service applications. The foundations for metal seal design have long been established in other industries such as aerospace, high pressure and temperature autoclaves, cryogenic and chemical industries. This paper will examine why metal Seal technology exists and to what extent downhole well completion equipment is affected.

INTRODUCTION

As new frontiers emerge in the oil and gas industry, new problems arise. Higher temperature and pressure, greater well depth and severe corrosion significantly affect downhole products. These factors combine to create severe performance and longevity problems which manufacturers of downhole equipment must work to solve. Polymeric seals in downhole equipment are the leading cause of equipment failure.1 Since reliability of the well completion is of utmost concern to today's operator, the push toward better seal systems has generated the current influx of metal seals.

Metal seals provide excellent service in many currently marketed products2. However, metal seals are not the panacea of downhole sealing requirements. As much as the industry would like to convert to metal seals, certain downhole products have yet to prove easily adaptable to metal configurations. Incorporating metal seals downhole requires basic seal design consideration. Extensive time and financial support is also required. In general, metal seal technology costlier to develop than non-metal.

Inroads have been made toward developing all-metal equipment. The subsurface safety valve is the first significant dynamic product to utilize all-metal seal technology. It is currently field proven and a readily available item. The safety valve utilizes all aspects of metal seal design and has laid the groundwork for products that follow.

SEALING THEORY

GENERAL

TO understand what makes a "good" seal, one must realize that there is no current accepted definition of the term "zero leakage". An acceptable seal in the oilfield may be totally unacceptable by aerospace standards. In general, however, zero leakage dictates the use of polymeric seals. When metallic seals are desirable, zero leakage must be quantified. For example, Advanced Technology Labs (G.E.) defines zero leakage to be less than 10−8 cm3 per second of helium at atmospheric pressure.
Exploration of Nearshore Placers Off Konkan Coast, West Coast of India
Authors: Gujar A.R. , Ramana M.V. , Rajamanickam G.V.
Published: October 2008

A detailed geological and geophysical survey comprising sediment sampling, short cores, shallow seismic profiling and magnetics covering about 90 sq. km. was carried out in the nearshore area (up to 20 m water depth) of 2 bays, Pawas and Purangad, Kookan Coast, Maharashtra to explore the offshore extension of promising onshore placers. The onshore beach placer sands extend to offshore to a water depth of 10 – 11 meters beyond which it is covered by clays. The surficial sands in these bays contain upto 93.69% of heavy minerals with appreciable amount of ilmenite and magnetite. Seismic profiles and short cores confirm the presence of heavy mineral rich sands below clays after 11 meters of water depth. The thickness of heavy mineral rich sand is 2–3 meters. The basement in the area is undulatory and has a N-5 trending depression (about 200–300 m wide) in Pawas bay which probably acts as trap for accumulation of sediments. The magnetic picture in the area shows positive correlation with heavy mineral placers and basement configuration. The offshore reserves of ilmenite and magnetite are inferred to be about 1 and 3 million tonnes respectively. The extensive onshore and offshore deposits offer encouraging possibilities for future integrated development.

INTRODUCTION

The occurrence of heavy mineral beach placers are known from many localities along the Indian Coast. The major deposits are along Kerala and Maharashtra on the west coast and along Tamil Nadu, Orissa and Andhra Pradesh on the east coast. The placer sands with varying proportion of ilmenite and magnetite have been reported from the areas of Ratnagiri and Sindhudurg district of Konkan Coast Maharashtra. The continuity of these coastal beach deposits is interrupted by morphological features such as cliffs, promontories and drainage features like creeks Cll1d tidal inlets. These deposits in general, occur as beach deposit Which is immediately in contact with the sea, as a dune deposit further inland, as bars in river and creek mouths and also in the low laying interior area behind the bars in the marshy lands. Patel (1936) and Roy2 (1958) surveyed these coastal deposits at many places. Their survey indicated 54.4% of magnetite and titano magnetite, 29.4% ilmenite, 7. Z'1o rutile with other constituents like tourmaline pyroxene, quartz, and feldspar along Purangad, but during their survey the Pawas beach was not covered. The average thickness of Purangad beach sands is about 1 to 2 meters. The reserve of ilmenite is estimated to be about 0.025 million tonnes and along with this titano magnetite is also present Roy2 (1958). These beach placers and adjacent Pawas beach placers are expected to extend in the offshore regions.
Glamis: A Subsea Satellite Development
Authors: Craig I.G. , Oldfield G.A.
Published: October 2008

Glamis is situated 8km south west of Sun?s Balmoral Field. Its development as a subsea satellite field represented a substantial extension of the Balmoral FPV and template facilities installed in 1986.

The three well development project was managed and engineered in house using proven Balmoral technology and experience wherever possible, although notable changes were necessary owing to differing design parameters and advances in technology.

INTRODUCTION

The Glamis Field is a 17.5 mm STR recoverable Jurassic accumulation. It was discovered in 1975 in 145 metres of water in Block 16/21a of the UK North Sea.

In 1985 three appraisal wells were drilled, tested and suspended as two future producers and one injector. The decision to develop the field was deferred until December 1987, more than a year after the Balmoral field came on streams.in order to optimise production profiles and fuel gas availability for the FPV.

The development comprises dedicated flowlines, control umbilicals, trees and protection structures, flexible riser system and a template manifold. Modifications to the Balmoral topsid.es facilities and subsea control system ?were also required.

During the development, economies of scale made it attractive to install extended well test (EWT) facilities to a nearby Blair prospect which lay in the pipeline right of way to Glamis. This project was run concurrently with Glamis but is outside the scope of this paper.

INITIAL STUDIES

Although allowances for expansion were made in the Balmoral Field development (Ref 1), Glamis presented a range of significantly different problems

The Jurassic reservoir is deep, at 10,150 feet TVDSS; hot at 120°C; corrosive, with a MOL C02 percent of 1.78; contains a relatively high GOR of 1037 scf/stb and has wellhead shut in pressures of 2900 psig compared to 1650 psig for Balmoral.

Initial studies projected a production rate of 10,200 bbl/d for 4 years, sustained b.v an immediate water drive of 20,000 bbl/d. Gas production at plateau would be 7 mm sc fd and no artificial lift facilities would he required owing to the high GOR.

It was concluded that the reservoir would be best depleted by retaining the existing wells in a three well development, (Figure 1). Both of the producers would require side tracking later in the well life owing to projected water cut build up and to access a new updip location in the reservoir.

Fiscal metering of Glamis production fluids would have required the installation of an additional separation train and metering skid on the FPV.
Extended Reach Drilling From Platform Irene
Authors: Mueller M.D. , Quintana J.M. , Bunyak M.J.
Published: October 2008

Two wells extending out over two miles have been drilled by Union Oil Company of California (Unocal) from Platform Irene in the Pt. Pedernales Field, offshore California. These wells hold the record for the two longest reach wells on the West Coast.

Several wells around the world have been drilled beyond two miles, but none have accomplished this feat at such shallow, true vertical depths. The average angles (from rotary table to TD) for Platform Irene wells A-16 and A-17 are 70.9° and 68.2°, respectively.

This paper will present to the industry the concepts of a "Negative Weight Well" and "Drag Risk Analysis", and will focus on the innovative technology used to drill and complete a high drag well. The successful drilling and completion of these wells has enabled the future recovery of millions of barrels of oil originally expected to be produced from a second platform.

INTRODUCTION

Unocal and its partners, Gulf (now Chevron) and Superior (now Mobil), acquired Federal Lease OCS P-0441 in OCS Sale #53 in May, 1981. The Pt. Pedernales field was discovered in November, 1982 with the drilling of Unocal OCS P-0441 #1. Platform Irene was set in August, 1985 and the first well was spud in April, 1986. In March, 1987, tracts P-0437, P-0438, P-0440, P-0441, P-0444, and P-0510 were combined to form the Pt. Pedernales Unit consisting of seven partners.

Platform Irene is located in 242' of water approximately 4.5 miles from nearest land and 60 miles west-northwest of Santa Barbara, California.

Figure 1 depicts Platform Irene's location relative to the California coastline.

FIELD DEVELOPMENT

A viscous 15.8° API crude oil and gas are produced from the Miocene Monterey formation. The Monterey varies several hundred feet in thickness and consists of vertically fractured, thin-bedded and interlaminated cherts, dolomites, and shales.

Production was initiated in April, 1987 at the rate of 10,500 BOPD, 0% cut. Peak production of 23,500 BOPD was achieved in August, 1987 after eleven development wells were acidized.

It was originally intended to develop the south-east portion of the reservoir with Platform Irene and set another structure, Platform Iris, approximately two miles to the north-west, to develop the rest of the field. The setting of Platform Iris became uneconomic s oil prices plummeted.

OBJECTIVES

By drilling the high angle, extended reach wells from Platform Irene, it was hoped that the following objectives would be achieved:The need for the high capital costs of a second platform would be eliminated.The near-horizontal well bores would intersect more vertical fractures and cut more formation.Prove that not only could a "Negative Weight Well" be drilled and completed, but that it could be accomplished in an economic manner.
Development of Automated Offshore Drilling System
Authors: Fujita H. , Sato M. , Shiraishi N. , Wakiya Y. , Tanaka S.
Published: October 2008

The purpose of the project is to develop the "Automated Offshore Drilling System" and to establish its basic design.

Since 1984, research. investigation work. design. fabrication, and field test have been executed to develop the "Automated Offshore Drilling System" by Japan Ocean Industries Associations (JOIA), jointly with Mitsui Engineering & Shipbuilding CO., Ltd.(MES), and other member companies under the auspices of the Ministry of Trade & Industries (MIT!).

Field tests of prototype mud pulse MWD and demonstration tests of 1/2 (one-second) scaled pipe handling systems including racking system, top drive system, draw works, Auto Roughneck, Pipe Handler, etc. had been completed successfully.

INTRODUCTION

The oil & gas extraction from offshore fields has become one quarter(1/4) of the world product. This percentage is expected to increase, and the development targets of future offshore fields will move toward a harsher environmental area, i.e., deeper water and arctic areas.

On the other hand, "automation" is the demand of the times, in the industries and all human lives. however, the equipment and system on the drilling rigs seem to be far from automated. The major reason of the above is, the drilling operation strongly depends on experience and special skills of drilling crews. At the same time, a shortage of skilled drilling crews will become a critical issue.

The current low level of the day rates earned by offshore drilling rigs and the reduced level of drilling by oil companies, has reduced the R&D efforts. The oil companies and contractors are rather conservative, then the rigs with totally different drilling system such as National A10-32 are very few. Developments of robotic drill pipe handling unit such as Temco in Norway have not been succeeded.

R&D PROJECT

To meet the demands of the times, MITI has been promoting the "Highly efficient offshore oil & gas drilling project", to develop an "Automated Offshore Drilling System", and entrust its practice to JOIA.

This project, started in 1984, has a goal aimed atthe 1989 fiscal year to establish the basic design of the "Automated Offshore Drilling System". The project committee has been organized by JOIA with 12 member companies in Japan, to discuss the R &D work.

The philosophy of this project is to develop the "Automated Offshore Drilling System" as an extension of the present concept, the system can be applied to any type of existing drilling rigs with small modifications to some extent.

Among many sub-systems to be automated, the following five have been selected for this project:Central control &monitoring systemReal time measuring system (MWD)Mud control systemPipe handling systemBarge control system
Accurate Vertical Pile Installation by Using a Hydraulic Vibratory Hammer on the Arbroath Project
Authors: Ligterink A. , van Zandwijk C. , Middendorp P.
Published: October 2008

In the Summer of 1989 the Arbroath platform was installed on behalf of Amoco in the UK Sector of the North Sea. A part of the project involved the installation of two docking piles, for locating the platform accurately over the template, and four under-leg piles for giving initial stability to the platform, before the skirt piles had been driven.

The paper describes the use of a vibratory hammer, the ICE-14l2, during the installation of the docking and under-leg piles. It describes how the penetration by vibrator was predicted, and how during the initial stage of penetration, control was kept over the verticality of the pile. For the first time the pile inclination was measured continuously during penetration, providing the opportunity to correct the verticality as required. The paper highlights the principles and results of these measurements.

The paper concludes that the combination of vibratoryhammer and conventional hydraulic underwater hammer can be very effective for underwater pile installation. The pile verticality can be effectively controlled by continuous measuring of the pile inclination during vibration.

Introduction

A part of the Arbroath Project was the installation of two docking piles and four under-leg piles, all with an outside diameter of 1067 mm in addition to eight foundation skirt piles. The docking piles were required for an accurate positioning of the platform over the existing template, whereas the under-leg piles were needed to support the jacket during the actual piling and to avoid uneven settlements during driving and when standing unpiled in a Summer storm.

Because the verticality of some of the piles wasextremely important on this project and because of the uncertainty of the top soil layer, the piles were predriven with an ICE-14l2 vibratory hammer, and taken to final penetration by an IHC S-400 hydraulic hammer. Due to the water depth, the entire operation was performed under water.

To ensure the verticality during the initial penetration of the piles, two inclinometers were mounted on the vibratory hammer housing. Hard wiring ensured that the inclinations were read out on a display on deck of the semi submersible crane vessel.

Due to the smooth operation and because all piles were installed well within the tolerances, (the maximum pile out-of-verticality was only 0.75 degrees according to the instrumentation and 1.25 degrees according to a check by divers), the job was performed fully to the Client's satisfaction.

The Arbroath Pr01ect

The Arbroath project consisted of a 3300 tones platform, to be positioned with the aid of a crane vessel over a pre-installed sub sea wellhead template with a number of pre-drilled wells. The water depth at the locations was 93 m. The jacket was installed in 1989; the template having been installed 10 years earlier.
Ekofisk Reservoir Pressure Drops and Seabed Subsidence
Authors: Mes M.J.
Published: October 2008

Phillips Petroleum company Norway has measured the progression of seabed subsidence of the offshore Ekofisk field monthly from March 1985 through the present using satellites and seafloor pressure gauges. Subsidence rates derived from satellite data for the period from March 1985 through April 1988 have been correlated with reservoir pressure drops to relate reservoir pressure decreases to increases in subsidence. The crystal portion of the compacting field may contribute most to the seabed subsidence at the 2/4 H platform, located near the central portion of the field. The arguments are described. We used a cause and effect analysis as a mathematical tool. We derived that most seabed subsidence occurs approximately four months after a change in reservoir pressure and a 7 month history of subsidence caused by a unit drop in reservoir pressure. Data are listed, the interpretation and analysis procedures are described, and the interpreted final results are presented which describe:Pressure drops near the center of the reservoir correlate best to the seabed subsidence in the central portion of the field.A contemporary relationship between reservoir void age and seabed subsidence rate can be used successfully to relate reservoir pressure drops to subsidence increases.A tool to estimate short term subsidence properties from reservoir pressure drops or vice versa.

The study concerns itself only with short term subsidence effects. For long term predictions Phillips Petroleum Company has developed very sophisticated computer models. A description of these models and the use there of are excluded from the scope of this paper.

INTRODUCTION

Phillips Petroleum Company Norway is the operator for the Ekofisk field. This field is located roughly in the middle of the North Sea. Several platforms, placed near the center of this field, are connected by bridges. This group of platforms is referred to as the Complex. The field was discovered in 1969 and has produced oil and gas since 1971. Subsidence of the Ekofisk field was discovered in November 1984.

Phillips Petroleum Company developed very sophisticated two and three dimensional computer models to simulate compaction and seabed subsidence. These models and their physical, geophysical and geological background were discussed in an 1988 Offshore Technology specialty session dedicated to Ekofisk Subsidence. (Most of the papers presented in that session can also be found in the Journal of Petroleum Technology, July 1989 Vol 41, no.7). These models, driven by reservoir pressure, are used amongst other, to predict long term subsidence. The work that is presented in this paper is very pragmatic and qualitative by comparison. Its purpose is to correlate contemporary short term pressure changes to short term seabed subsidence. In this sense its intention is to provide additional insight in the subsidence phenomena.
Axial Capacity of Offshore Piles in Clay
Authors: Karlsrud K. , Nadim F.
Published: October 2008

The paper describes two main aspects related to axially loaded offshore piles in clay: methods to determine the local ultimate skin friction and effects of cyclic loading on axial pile capacity. A new 'NGI-method' for determination of ultimate skin friction is described in detail. The method is primarily based on predicting the ultimate skin friction from the state of effective stresses at onset of pile loading, coupled with untrained shear strength properties of severely remolded and reconsolidated clay as determined by direct simple shear tests. A software system for evaluating the response of an offshore pile is described. Based on a case study for piles in soft plastic clay, it is shown that the pile capacity is significantly reduced if the cyclic loads comprise a large portion of the design loads. The influence of pile length (flexibility) is also demonstrated.

INTRODUCTION

Significant efforts were made in the past decade to improve the methods of determining the axial capacity of offshore piles in clay. These include development of an extensive pile load test data base (Olson and Dennis1) and related statistical studies on the reliability of various common empirical design rules (Olson2, Tang3, Lacasse and Goulois 4); a number of large and small scale instrumented pile load testing programs and development of new theoretical models.

As a result of these efforts, the API-RP2A 5 design guidelines underwent a pronounced change in the 17th edition, where the undrained shear strength reduction factor, ?, was related to the in situ normalized untrained shear strength ratio, rather than the absolute value of the untrained strength. Furthermore, in the commentary to the 17th edition the necessity of separately evaluating the effects of pile length or flexibility and cyclic loading on the pile capacity was pointed out.

During the period 1980-84 the Norwegian Geotechnical Institute (NGI) undertook a comprehensive pile load testing program in an over consolidated clay deposit at the Haga test site, Karlsrud and Haugen 6,7 A total of 27 individual pile tests were carried out on 5 m long, heavily instrumented steel piles with a diameter of 15.4 cm. The pile loads covered a wide range of static and cyclic loading combinations, mostly in tension, but also in compression. Based on the results of these tests, various theoretical concepts and models were developed for analyzing the pile clay interaction during installation, reconsolidation and pile loading. This paper concentrates on two main aspects:Determination of the ultimate static skin friction after full set-up according to the "NGI-method", and comparison to API and some other empirical design rules.Determination of effects of cyclic loading on the axial capacity of offshore piles according to the computer model PAXCY developed by NGI.
Balmoral FPV: Three Years On
Authors: Harrington G.L. , Davis A.J. , McIntosh C.J.
Published: October 2008

The Balmoral Floating Production Vessel (FPV) has been on location in block 16/21 of the UKCS since August 1986. The Vessel has produced virtually continuously in some of the worst weather experienced in the North Sea for several years.

This paper presents the first 3 years of the operational 1ife of the Balmoral FPV. It describes the major plant items and how they have behaved in service. Weather sensitivity is discussed along with modifications which have been made.

Introduction

The Balmoral FPV was built in Sweden and arrived on location in August 1986. First oil came in late November of the same year and the rate gradually built up to plateau as wells were brought online. Figure 1 shows the production profile since startup. A description of the vessel, along with design criteria has been presented previously1. Briefly, the floating vesse1 acts as the production faci1ity to separate the gas, water and oil from 13 template and satellite wells. It is connected to the sub sea template by flexible risers. The facility also has the necessary equipment to perform work overs, drilling, water injection and gas lift.

Down hole/Gravel Pack/Sub sea

The Balmoral Field has been developed using 10 template and 3 satellite production wells and 6 satellite water injection wells - see Figure 2 for field location map. All the wells were comp1eted prior to the arriva1 of the FPV on location and startup of production. In addition, 2 further fields have been developed using the Balmoral FPV facilities: the Glamis field which consists of 2 satellite production wells and one satellite water injection well and the Blair field which consists of one satellite production we11. Production from these fields commenced in the summer of 1989.

Initially all of the Balmoral wells were gravel packed for the purposes of sand control. However during the completion of a satellite production well, the gravel pack resulted in such a significant reduction in productivity that the well was unable to meet its production target. As a result the gravel pack was pulled and the well recompleted without a gravel pack. In addition, there have been 2 gravel pack failures to date. These were due to chloride stress corrosion cracking of the wire wrapped screens induced by stimulations of the wells with HCl and HCl/HF acids. Subsequent to this new stimulation treatments have been designed based on acetic and HF acids.

Sand production from the wells is being monitored by the use of sand probes on the FPV although they have not proven to be very successful. At present the sand production rates are such that it does not constitute an operational problem. However should such a problem arise then serious consideration will be given to regravel packing these wells.
The Design and Operation of the "Not Normally Manned" Amethyst Gas Field
Authors: Maciver L.M. , Khatib H.M.
Published: October 2008

The Amethyst Development incorporates a combination of well proven techniques in a novel manner to achieve a multi platform, remotely controlled gas field.

The field is located in the UK Sector of the Southern North Sea, some 40km offshore.

The reservoir is gas bearing with higher than average condensate yield. Its aerial extent is c. 106 square km requiring four platforms and up to 21 production wells to deplete it.

The fields will produce a peak rate of 250 MMSCFD of gas in the first contract year starting October 1990, followed by a peak rate of 300 MMSCFD for the subsequent six years of production. Thereafter production will decline as reserves are depleted. Daily condensate rate is expected to peak at 3.4 MBPD during the plateau period.

The development plan encapsulated a number of interesting features, such as onshore gas compression, onshore fiscal metering, full control and operation from the landfall terminal, all combining to achieve economy with enhanced safety.

INTRODUCTION

The Amethyst field was a first round UKCS license - its development was from the outset foreseen as an engineering challenge.

Some seventeen appraisal wells were drilled to establish the reservoir and various development studies were carried out in the quest for a viable investment. These early studies were centre on a conventional development approach, having an offshore gas gathering system (with unmanned satellites) and the requisite manning and gas compression facilities offshore.

This approach did not yield the necessary economic results, or indeed, offer the safest solution.

In 1986, a more target Ted approach to determine a development plan was established and key objectives set which focused on capital and operating cost reductions, simplification of the facilities, and improved safety, with utilization of the infrastructure at the landfall

This effort was successful and the development plan was given approval in June 1988.

THE DEVELOPMENT PLAN

The development plan as approved in June 1988 is shown in perspective view in Figure 1.

The adoption of this plan achieved the following key features:elimination of reliance on rotating equipment offshore during normal operation;multi-platform remote control from shore;minimal onboard platform facilities;remote spearing of 30 inch pipeline;power supply by sub sea cable;wet operation of pipeline with corrosion inhibitor;export of methanol from the landfall terminal by piggy-back pipeline;maximum utilization of landfall infrastructure;location of compression facilities onshore, some 5 years into field life;telecommunication by digital signal; use of a proprietary package for the field control system.