bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variable-Speed AC Drives for Drilling Plants
Authors: Haeussler A. , Mohr G. 
Published: October 2008

ABSTRACT
This paper relates to the development work on a system of variable-speed drives consisting of an AC motor and frequency converter for use on drilling rigs. The object is to introduce modern AC drive technology to drilling rigs to replace the conventional DC drive system. The report covers the specification of the crucial requirements, the steps of development and test and results, features and advantages of the drive system.

INTRODUCTION
The converter-fed variable-speed DC motor is nowadays still the standard drive for rotary table and top drives, for draw works, mud and cementing pumps. It satisfies the requirements for drives installed on drilling rigs.
However, DC drives are characterized by their carbon brushes, whose wear is markedly dependent on the prevailing operating and ambient conditions. The material worn away from the brushes can accumulate in the vicinity of the commutator and lead to flashover at the brushes and the commutator. The frequent maintenance and servicing required to prevent malfunctions represent a considerable cost factor.
The motors for rotary table and top drives, for draw works, and in some cases for the pumps, are often located in hazardous zones of the drilling rig.
For this reason the drive motors must be of explosion-proof design. In the case of DC motors the sole possible type of protection is "pressurization" (EExp). This type of protection is costly. Moreover the cooling air must be routed from the safe zone to the motor by means of pipes and the exhaust air from the motor to the safe zone by means of ducts.
In the case of offshore plants air-to-water coolers are often employed, which, however, must also be connected to an air supply system in addition to the water. In both cases considerable expenditure is involved for monitoring of the cooling air and cooling water systems and for purging the motor prior to starting. Apart from the capital outlay for this equipment the maintenance and servicing costs must be taken into consideration.
Line-commutated converters, which are generally in six-pulse bridge connection, exert an influence on the power supply system due to their operating principle, namely phase control of voltage half waves. As a result the reactive power demand on the power supply system and the power factor is a function of the motor speed. Where power is supplied from diesel generators sets, this fact must be borne in mind when dimensioning the units.
In addition rectifiers also generate harmonics of definite orders which cause voltage distortion in the whole network. Additional heating is caused as a result of this distortion, which must be taken into account in dimensioning the generators and the loads.
Where power for the drilling rig is taken from a public supply line, special measures must be taken to meet the power utility regulations with regard to the compensation of reactive power and suppression of harmonics. Such measures may involve considerable additional expenditure.
Structure of Continental Shelf of Morocco Based on Sonobuoy Results
Authors: Holik J.S. , Rabinowitz P.O. 
Published: October 2008

Abstract
Multichannel seismic meaurements (MCS) together with sonobuoy data were analyzed in the shallow water portions «200 m) of the NW African continental margin. The untuned sound source and acquisition techniques were designed for use in deep water. Thus, the shallow water shelf data was reprocessed using velocity filtering. Though the processing improved the data quality, the data is still rather noisy. Refraction velocities obtained from sonobuoy experiments over the shelf, however, yielded excellent measurements. Results here document the seaward extension of major continental structural and geological features such as the Moroccan Meseta, the Atlas mobile belt and the South Atlas Basin.

Introductjon
RN Robert Conrad sailed in the spring of 1983 off Morocco with the intent of collecting multichannel seismic (MCS) data, gravity and magnetics, and conducting sonobuoy reflection/refraction experiments. A primary scientific objective of this cruise was to study the early rifting and separation history of the northwest African margin. The cruise tracks were designed to fill a gap in the existing geophysical data in the area in order to explore the crustal structure of the deep-water (&gt;200 m) portions of this passive continental margin1" Although the geophysical acquisition parameters (untuned sound source and relatively long hydrophone intervals) were designed for deep water experiments, data were also collected over the shallow water portions of the margin. Figure 1 shows the location of the study area as well as the location of the sonobuoy experiments.
This paper describes our efforts to use these shallow water data. The data is divided into two parts. The first describes the reprocessing of the MCS data and the second covers the sonobuoy results. Efforts are made to tie the two data sets together in order to determine the structure of the shallow water portions of the Moroccan continental margin.

MCS
After initial processing of the MCS data2, the shallow water portions were reprocessed with the aim of improving the signal to noise ratio. The shallow water on the continental shelf (approx. 200 ms) coupled with the untuned sound source and the fact that a Jurassic carbonate platform of high seismic impedance exists at shallow depth below the shelf3, resulted in a seismic section obscured by ringing. Velocity filtering based on the technique described by Ryu4 was employed in an attempt to remove some of the spurious noise.
The effect of the velocity filtering was to dramatically improve the signal/noise ratio in the common-depth point (COP) gathers. Figure 2A shows a COP gather before filtering and 2B afterwards. The filtering effectively removed both the refraction and the water wave arrivals from the gather as well as much of the ringing in the upper 3 seconds. Although the noise above seafloor could have been removed by a mute during stacking, the ringing below seafloor could only be removed by a process such as velocity filtering.
Advancements in Liquid Hydrocyclone Separation Systems
Authors: Schubert M.F. 
Published: October 2008

ABSTRACT
Since introduction in 1983, the Vortoil ® Hydrocyclone has become widely accepted in the oil and gas industry, with treating capacity of over 7 MM barrels of water per day. This success is largely due to the ability of this technology to meet environmental discharge standards while offering significant installed weight and space savings and reduced operating costs.
Further research has enhanced the separation efficiency of this technology in anticipation of more stringent environmental standards as well as adapting the hydrocyclone for primary separation of produced oil and water. The applications of the hydrocyclone technology to be discussed in this paper are:Hydrocyclone system design,Hydrocyclone designs for enhanced separation,Low pressure operation,Hydrocyclone systems for primary production separation.
Test results have shown significant improvement in oil removal efficiency for deoiling hydrocyclone, enabling lower oil content levels for produced water discharge. The improved designs enhance separation at great 1y reduced pressures. Where insufficient feed pressure exists, systems using correctly designed and operated centrifugal pumps result in a cost effective, low shear solution.
Several field tests have been conducted to evaluate the ability of the hydrocyclone to make bulk oil/water separations. Results have shown that in high water cut product ion, hydrocyclone effectively remove bulk water, leaving less than 1000 ppm oil in the water stream and return a relatively dry oil stream. Conversely, in systems with a relatively low water content, the Dehydration Hydrocyclone has been able to meet BS&W specifications.

INTRODUCTION
The deoiling hydrocyclone provides a cost effective method to handle increasing water production, alleviating bottlenecks in many production systems. The ability to de-bottleneck water treating systems has in many instances a 1lowed operators the flexibility to increase water floods and production rates, thus increasing oil production and extending reservoir 1ife. In order to further expand the applicability of this technology, a two year research program was undertaken to improve efficiency and low pressure operation of the technology.
A Study on Upending Procedure of Prefabricated Tendon of TLP
Authors: Morikawa Masao , Suzuki Hideyuki , Ishikawa Kuniteru , Yoshida Koichiro 
Published: October 2008

ABSTRACT
Research and development of the TLP have been performed in the "Offshore Oil & Gas Production Platform Project" of Japan Ocean Industries Association (JOIA) promoted by the Ministry of International Trade and Industry, Japan (MIT!). In this project, the tendons which are planned to be fabricated and assembled on the land in an overall length will be horizontally towed to the site. After that, they will be installed there. As one of methods for the installation, the tendon in the upending procedure is planned to be dropped under the free falling condition. In the installation under the free falling condition, it is necessary to estimate the maximum stress and the installation time.
Therefore, the experiments for the upending procedure under the free falling condition were performed in the ship model basin in order to clarify the motion and stresses of the pre-fabricated tendons. After that, the simulation analysis was carried out using the time domain and non-linear FEM program. In this simulation analysis, three types of the drag force coefficients were selected. The experiments of the hydrodynamic forces acting on the oscillating cylinder in the steady flow were performed to obtain the one of the drag force coefficients at the resonant region caused by the vortex induced vibration on the tendon. The results of the simulation analysis were compared with ones of the experiments for the deformation and the stresses of the tendons. When the drag force coefficient which was dependent on the falling velocity was used in the simulation analysis of the upending procedure, the experimental and the calculated results coincide qualitatively and quantitatively.

INTRODUCTION
The offshore oil and gas development is expanding in larger water depth and in severer environment. In this trend, the TLP (tension leg platform) is considered to be the most promising concept. Recently, many kinds of projects and concepts of TLP are presented. In these TLPs, many types of the tendons are also presented. One of the most promising type of the tendons is a light weight tendons which have been selected in the tension leg well platform, called TLWP, in Gulf of Mexico. In the light weight tendon concept, the thickness and the outside diameter can be selected in order to obtain the neutral buoyancy. This type of the tendons can increase the payloads on the deck. The behavior of these tendons are investigated not only the strength in the working condition but also the method in the towing condition and the installation 1,2If the light weight tendons are fabricated by the welding process in their overall length on the land, the cost for the fabrication and the time for the installation are decreased in comparison with the tendons which are connected by the thread joint at the site.
Improvement in Tubular Jacket Closure Weld Fatigue Performance Through Alternative Fabrication Techniques
Authors: Marshall V.G. 
Published: October 2008

ABSTRACT
This paper describes an alternative method for making circumferential brace closure welds in tubular jacket structures from that used in North Sea jacket construction to date.
The method has been developed with the objective of improving quality reliability and fatigue performance in the light of premature service failure of these joints on some structures.
The paper examines the alternative approach against current methods and presents data on fatigue test performance to support the case for S-N curve classification to class F per UK Guidance Notes.

INTRODUCTION
The requirement to weld the tubular intersection joints of large North Sea jackets from both sides, coupled with the need to furnace stress relieve these joints leads to a nodal sub-fabrication construction method. In this approach chord and brace intersection region are fabricated as a can with an array of short stubs shop welded from both sides. These 'nodes' are then incorporated into the structure on the erection site.
Such methodology necessitates the specification of circumferential closure joints between node stubs and incoming brace members.
The closure welds, which generally occur at the first circumferential seam of the brace and often incorporate an internal thickness transition taper are difficult to make since access for welding is available only from the outside.
Furthermore, the reality of heavy jacket construction means that the desired quality of fit up is regularly not achieved and in situ remedial welding is required before closing the joint.
In this paper an alternative strategy for making these in situ closure welds is described, together with the results of tests carried out to prove the fatigue performance of the completed joint detail.
The alternative technique incorporates the use of a permanent steel backing.
While initial reaction to the use of such a detail is generally sceptical it is argued that real benefits are available both in respect of fatigueperformance and construction practice.

CURRENT CLOSURE WELD EXPERIENCE

Method
The present method adopted for making single sided circumferential brace closures is to specify an open root joint using a detail similar to that shown in Figure 1.
The optimum gap for welding such a joint is 4.0 mm although a variation givinggaps between 3.00 mm and 5.00 mm can be accommodated with comfort.
The welding skill level required to make such joints, to a standard requiring freedom from planar type defects, is very high, even under optimum conditions. The environmental conditions prevailing during site construction, coupled with the actual variations in fit up which occur, conspire to disadvantage the most skilled welder to the point where weld quality levels are compromised.
Titanium Stress Joint for a TLP Tendon System
Authors: Valenzuela E.D. 
Published: October 2008

ABSTRACT
This study presents the technical feasibility of replacing a connector and flex-joint with a titanium stress joint and a collet connector as components of a tendon system for a Tension Leg Platform (TLP). A detailed analysis of this new tendon system is presented for 2,000 feet of water depth in the Gulf of Mexico. The main conclusion of this study is that this new approach is feasible and replaces effectively the flex-joint used in previous TLP tendon designs. The new system has no moving parts, long fatigue life and works even better for the deep water cases.

INTRODUCTION
Figure 1 shows the general layout of a TLP platform with a tendon system anchored to the foundation template. The purpose of this study is to demonstrate the technical feasibility of replacing the connnector and flex-joint used in conventional TIP tendon design, with a titanium stressjoint and collet connector tha thas a stinger. The titanium stress joint provides the required flexibility for the maximum angular offset at both ends of the tendon. The collet connector provides the latching capabilities of the tendon to the receptacle of the foundation template. A stress joint connection at the bottom or top receptacles induce high bending moments at both ends of the tendon due to the lateral motion of the TLP. The stinger increases significantly the strength of the connector to resist high bending moments. The new tendon system uses the stinger approach at both ends of the tendon.
Hutton and Jolliet, the only two TLP platforms installed as of 1992, use a flex-joint at both ends of the tendon system. Hutton TIP uses at the bottom a Vicker's connector design with a collet locking system that engages the male stinger into the female receptacle located on the ocean floor. The Murdock flex-joint is built into the anchor housing. The fabrications of these joints use alternate layers of elastomer and partial spheres of stainless steel reinforcements to provide the required axial and angular spring area to accommodate a maximum angular offset of 16.6 degrees. The design of the tendon system for Snorre TLP follows very closely the design adopted for Hutton.
Jolliet follows a different design with a different latching mechanism at the bottom. Figure 2 shows the approach used in Jolliet for the bottom connection. The fabrication of the receptacle for the bottom tendon connection uses a load ring forging that has a cone shaped rolled plate skirt. The load ring assembly is welded into a structural stiffener fabrication which makes up the foundation template. The shroud of the connector has a slot that allows the lateral engagement of the male back flange of the tendon. The load ring and skirt assembly match the outward orientation of the tendon receptacle slot. The flex-joint is a ring built into the bottom part of the tendon. Several layers of elastomer bearings and metal sheets define the flex-joint. The fabrication of thetop tendon connection receptacle also uses a load ring forging with a cone shaped rolled plate skirt.
Enhanced Safety With New Subsea Intervention BOP for Horizontal Wells
Authors: Eriksen Gunnar , Bergum Bernt , Møsvold Harald 
Published: October 2008

ABSTRACT
Of the three subsea wells, drilled so far at the Oseberg field, two wells (drilled in 87/88) have a slight deviation to the true vertical, while the third well has been horizontally drilled (91) in the Gamma North Reservoir. This well will be producing gas for injection into the Oseberg Alpha Reservoir,
To enable service of horizontal parts of this last drilled well, use of coiled tubing operations will be necessary. When introducing coiled tubing in operations with X-mas tree and completion/workover riser from a floater, a safety problem occurred with respect to shut in of the well,
This ended up with the Subsea Well Intervention BOP (SWIB) where Ram Blow-out-preventer technology was used. Additionally, in order to ensure safe operation in case the floating rig drifting off location, an Emergency Quick Disconnect Package (EQDP) was placed on top of the SWIB.

INTRODUCTION
The Gamma North reservoir was developed by Norsk Hydro and its five partners*, as part of the Oseberg phase two development, and completed in October 1991. The Oseberg Field is located in blocks 30/6 and 30/9 in the Norwegian Sector of the North Sea. The Gamma North Structure, part of block 30/6, was decided to be developed with one subsea well, in order to exploit its gas reserves for reinfection into the main Oseberg reservoir.
However, the nature of the structure also allowed the development of a thin oil layer, which required the drilling of a horizontal section of approximately 700 m. This means that the subsea well, located approximately 9 km. away from the Oseberg C platform as shown in Fig. 1, initially will be producing 10.000bbl/d (max) of oil through an 8" pipeline before the gas production starts. Additionally a 3" service line and an electro-hydraulic umbilical were installed connecting the Gamma North satellite to the Oseberg C platform.
The philosophy for all the subsea equipment in the Oseberg Field is to be able to interchange the equipment between the various wells (two subsea wells B49 and B50 were put in operation in 1988).
When completing the horizontally drilled Gamma North well, only minor wireline operations were possible, To be able to service the horizontal part of the well, use of coiled tubing operations are necessary. When this was brought forward, the equipment did not comply with the operating philosophy safetywise. The need for more sophisticated cutting mechanism to cut coiled tubing was looked for. Since the similarity between drilling operation and coiled tubing operations are striking when coming to pressure control, it was obvious to use the same well-known drilling BOP technology for coiled tubing operations. This led to the development of the SWIB, Subsea Well Intervention BOP.
The new Subsea Well Intervention BOP was put on order in May 1991.
An Improved Method for Calculating the Contribution of Hydrodynamic Chain Damping on Low-Frequency Vessel Motions
Authors: Dercksen Albertus , Huijsmans R.H.M. , Wichers J.E.W. 
Published: October 2008

ABSTRACT
The computation of low frequency mooring forces on a tanker exposed to survival conditions requires knowledge of the hydrodynamic excitation and reaction forces. The low frequency excitation is caused by wave drift forces. The reaction forces on the tanker are a combination of added mass forces, wave drift damping forces, viscous forces and damping forces due to interaction with the mooring chains.
Withers [1] showed that for a chain turret moored tanker the interaction forces between the mooring system and the tanker contribute significantly to the low frequency motions of the tanker. In [2] Huijsmans presented an approximate method to include the interaction forces due to high and low frequency motions of the chain-turret moored tanker.
In this paper a direct simulation method for a chain-turret moored tanker will be applied for the correct instantaneous low and high frequency motions ofthe tanker, including the dynamic behaviour of the mooring chains. The latter will be modeled by a lumped mass method.
Comparison will be made of the direct Simulation method and an approximate method using the average chain damping. An evaluation of the chain damping contribution will be made using model test results and computations.

INTRODUCTION
A moored tanker exposed to irregular head seas performs small amplitude wave frequency pitch, heave and surge motions and relatively large amplitude low frequency surge motions around a mean surge displacement. The mean surge displacement and the low frequency surge motions are due to the second order wave drift forces. Since the total damping of the low frequency motions is small, and in irregular head seas the frequency of the slowly varying forces corresponds to the natural surge frequency of the system, resonance occurs. Large low frequency surge motions and consequently large mooring forces may be the result.
For the design of the mooring system, the large amplitude motions and the corresponding forces are required and it is therefore of eminent importance to have knowledge about the low frequency excitation and reaction forces. The excitation and reaction forces as acting on a chain turret moored tanker are given below:current velocity dependent wave drift forces/wave drift damping;relative viscous/current force;relative wind force;inertia force due to virtual mass of thetanker;reaction force caused by the mooringsystem.
All but the last item in the above list have been extensively discussed byWithers [3]. The contribution of the mooring system to the low frequency surge motions has been a subject of considerable attention in the past years.
In a static sense the reaction force on the tanker moored by a chain-turretsystem represents the load displacement curve, being the restoring force. In reality, due to the low and high frequency motions of the turret, the chains are movingthrough the fluid.