bluuebunny/crossref_metadata_2025 huggingface dataset:
Ore Assays of Massive Sulfides From Three Spreading Centers
Authors: Morgan C.L. , Selk Bruce W.
Published: October 2008

Ocean Minerals Company (OMCO), a deep seabed mining consortium has, through its general contractor, Lockheed Advanced Marine Systems, analyzed massive marine sulfide samples from three sites on the Juan de Fuca Ridge, one site on the East Pacific Rise (near 2PN), and one site on the Galapagos Rift, for the concentrations of Ca, Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd and Pb. The samples were collected with dredges and submersibles, and were generously provided to OMCO by government and academic investigators. It is possible that marine sulfides may be a future commercial source of Cu, Ag, Zn and other metals and those studies of these young, relatively unaltered deposits will also provide useful guidelines for the location of unexplored and commercially viable land deposits of marine origin. OMCO has supported this comparative study of the major and minor element composition of sulfides from these three medium-rate spreading centers to obtain a preliminary estimate of ore grade variability and to identify likely sites for future exploration.

From the samples analyzed to date, it appears that there are significant differences among the sulfide compositions characteristic of each spreading center. The samples from the Juan de Fuca Ridge are all Zn-rich (maximum concentration greater than 50%) with significant concentrations of Ag (6–12.5 Tr. oz/metric ton). The 21°N East Pacific Rise samples are either Zn-rich or Cu-rich, but have lower Ag concentrations than the Juan de Fuca Ridge samples. Samples from the Galapagos Rift are Cu-rich and Fe-rich. Silver concentrations in these samples appear to be inversely correlated with water depth. Though the high metal values obtained are encouraging and clearly justify the continued support of the several U.S. projects which are presently investigating such deposits worldwide, much additional information is needed to justify serious commercial interest. The distinct compositional differences noted between spreading centers may well be regional in character, and may imply basic differences in the source rock, the development of the hydrothermal fluid, or the deposition process.

INTRODUCTION

Sixteen samples of marine massive sulfide deposits were recently provided to Ocean Minerals Company (OMCO) by academic and U.S. Government researchers for preliminary ore assay analysis. These samples have been subsampled and analyzed by Lockheed for Ca, Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd and Pb using atomic absorption techniques. The samples were collected from very young hydrothermal deposits at five sites; three on the Juan de Fuca Ridge (the Endeavor segment, the Axial seamount, and the southern Juan de Fuca Ridge), one from the East Pacific Rise at 21°N and one from the Galapagos Rift at 86°W. The samples were collected by both dredges and manned submersibles. The purpose of this paper is to report the results of these preliminary analyses. Since identical methods were used in the analysis of all samples, the data set provides a good means of comparison of deposits from different locations.
Articulated Riser for Subsea Production System (SPS)
Authors: Nakamura S. , Sasaki M. , Kuwabara K.I.
Published: October 2008

An articulated riser having three universal joints to give high flexibility for a floating storage and production platform has been developed. All pipes in the riser including those for the through flow line (TFL) services, are not flexible pipe but are made of steel. Pipe swivels are applied to accommodate the articulation of the universal joints.

This riser can be disconnected at the upper and lower ends and retrieved for periodic maintenance. The installation method for the riser, the underwater positioning system for installation, and the guiding mechanism to mate with the riser base have also been developed and verified at sea tests. Finally, during the offshore pilot test of SPS, the riser functioned effectively with no leakage at any part of the pipe lines.

INTRODUCTION

A Japanese National R&D project to develop "Subsea Production System (SPS)" was started by the Agency of Industrial Science and Technology, under the Ministry of International Trade and Industry (MITI), in September 1978 and was completed at the end of 1984.

The overview of the project is reported in another Paper, OTC 4963.

This project proceeded separately as a total system and four subsystems, Le. wellheads, pipelines, manifold and riser-storage systems.

Finally, the equipment manufactured based on the results of the development in each subsystem were installed on the seabed and connected to each other. After that, type offshore pilot test was carried out using a simulation well in 1983.

Production conditions for the riser-storage A Japanese National R&D project to develop "Subsea Production System (SPS)" was started by the Agency of Industrial Science and Technology, under the Ministry of International Trade and Industry (MITI), in September 1978 and was completed at the end of 1984.

The environmental and the basic requirements Finally, the equipment manufactured based on the results of the development in each subsystem were installed on the seabed and connected to each other. After that, type offshore pilot test was carried system were Requirements installation tools. provided by the total system group. included guide lineless, driverless and maintenance and work over by TFL tools.

The riser-storage system is roughly divided in two parts lone is the floating storage tank which carries the production treatment plant and the offloading equipment to the shuttle tankers.

The other is the riser connecting the storage tank and the equipment on the seabed.

A monocolumn, cylindrical, semi-submersible storage tank moored by multiple catenary anchor lines was selected. The produced crude is stored in the tank compartments replacing sea water and is offloaded by being replaced with sea water. On the deck above the storage tank, the treatment plant and the other necessary equipment are installed. The shuttle tankers are moored directly to the storage tank to offload the crude.
Wave and Motion Measurements on Board the Semisubmersible Pipelaying Barge LB-200
Authors: Weyers L.J. , Vlaming M. , Verdonck J.
Published: October 2008

For a barge laying pipe under rough weather conditions at sea, pitch, roll, heave, surge, sway and yaw are important phenomena to be known and monitored. It is of vital importance that the static and dynamic stresses in the pipe are kept within prescribed limits. The static bending stress in the pipe at the upper bend, on the stinger, and at the lower bend, near the sea bottom touch point, are highly dependent on the deformation of the pipe. The horizontal tension of the barge mooring lines will effect the static pipe deflection. However pipe deflection does not depend only upon static forces. Dynamic forces caused by dynamic barge motions add an important part to the stresses in upper and lower pipe bends. Too much stress will cause pipe buckling in the bends and results in much delay time and costs as the pipe, already at the sea bottom, will have to be replaced. Usually extensive calculations and model studies are performed in an early stage of the pipe lay project.

This paper gives a general description of the barge motion measuring system used on board of the pipelaying barge LB-200 owned by HcDermott International Inc., North Sea Division. In the Norwegian sector of the North Sea the LB-ZOO was contracted for the Statpipe Development Project requiring more than 300 miles of pipelines, which will bring gas from offshore fields to Norway. One of these rich sources is the Statfjord field, where oil as well as gas has been found. In 1983 the LB-ZOO layed the pipeline to shore at Karmoy Island and went on to lay 125 miles of 28-inch-diameter line to block 16/11, crossing the Norwegian Trench in water 300 m deep. Lay rates of 2.3 miles a day were made in the western slope of the trench toward Karmoy.

All motions of the barge i.e. pitch, roll, heave, surge, sway and yaw had to be monitored continuously. The pipe had to be disconnected once those movements reached a certain magnitude due to weather circumstances. Another condition was that an historical record of all movements mentioned had to be kept on file.

This paper describes the realization of the motion monitoring system. The following demands had to be fulfilled:automatic computer controlthe least possible maintenanceonline continuous monitoringcontinuous filing

INTRODUCTION

The lay barge LB-200 is roughly 160 m long and it has a width of 60 m. The deck is supported by six columns placed on two pontoons. Fig. 1 gives an overall view. A twelve mooring line system keeps the barge in position. Pitch motions are important for pipe laying because of the danger of pipe buckling. Plus or minus two degrees of pitch motion was set as the limit during operations. Beyond this limit operations were stopped.
Ice Forces Exerted on a Conical Structure in the Gulf of Bothnia
Authors: Maattanen M.P. , Mustamaki E.O.
Published: October 2008

A joint Finnish consortium of industry and state research organizations has designed, constructed and instrumented a conical test structure for full-scale measurements of ice forces against a conical fixed off-shore structure. The structure and its instrumentation are described. The test cone was installed around the existing Kemi-I lighthouse in the Gulf of Bothnia.

Field measurements have started. The intention is to measure the action of all typical first-year ice features, including pressure ridges, with an average sheet ice thickness of 0.8 m. Model tests with a scale ratio of 1:15 have been conducted and the results are described. Theoretical models of ice forces against a cone will be calibrated using both the model and full-scale test data. This will provide a reliable basis for extending ice force predictions to arctic conditions, where the ice is about 2 to 3 times as thick as in the Gulf of Bothnia.

INTRODUCTION

The advantage of a conical shape at the waterline of an off-shore structure is that the failure mode of level ice is flexural, which greatly reduces ice loads compared to crushing against a vertical structure. Both horizontal and vertical ice force components develop and the latter has a stabilizing effect, which is important in deep water applications. The underwater part of the structure can then be narrower, which also results in reduction of loads from pressure ridges. At water depths greater than 30 m the cone is regarded as the most economical choice for a fixed bottom-founded structure.

The concept of the cone has been well known for more than 20 years. There are many theoretical models /1, 4, 5/ for predicting ice forces against a cone and model test results as well /3, 5, 6/. However, no full-scale field ice force data are available to evaluate theoretical models. Only tentative results have been published for a cone with a 1.5-m'waterline diameter in the St. Lawrence Seaway /2/.

Theoretical models of the ice forces exerted against a cone take account of the formation of radial and circumferential cracks in the oncoming ice sheet, friction between the ice and the structure, the work required to raise broken ice floes up along the cone and for them to be pushed aside. Some models have been evaluated in model tests but due to the large scale ratios, there are many uncertainties in the prediction of ice forces for full-scale arctic off-shore structures.

The objectives of this research are to acquire data for evaluating theoretical models of ice forces against a cone. The test cone around Kemi-I lighthouse in the Gulf of Bothnia will provide full-scale measurements of the ice forces against a conical structure with level ice up to 1 m thick and with first-year pressure ridges and rafted ice.
Dip Moveout And Prestack Imaging
Authors: Gerlad H.F. , Wang S.Y. , Pan N.D. , Zhang Z.
Published: October 2008

Dip moveout is presented as a data conditioning process in which a diffraction surface in midpoint-offset-time space is transformed into a surface of revolution. Pre-stack imaging operates on constant-time slices of the data, after dip moveout has been applied, in which diffractions appear as circles, adds data along these circles, and plots the sum at the largest offset point of each circle. After both operations, a standard velocity analysis and stacking algorithm produces a migrated section. Both operations are independent of velocity.

INTRODUCTION

Two problems commonly associated with CDP stacking are (1) a loss of resolution because the reflection point moves updip as the offset increases and (2) the stacking velocity depends on the dip angle of the reflector. The first problem is particularly severe if the reflection point moves across a fault as it moves updip, as indicated in Figure 1. The second problem means that stacking velocities are not appropriate for migration after stack.

Dip moveout (DMO) helps with both problems, as first explained by Judson et al. (1976). There is less loss of resolution because the gathers, after DMO, have events with common reflection points. Also, the stacking velocity is not so dependent on the angle of dip and is more useful for selecting velocities to migrate the data after stack. However, the stacking velocity is estimated at the slant travel time T2 and not at the vertical travel time To, as one would wish.

DMO can be followed by another processing step called pre-stack imaging (PSI). After PSI, the data are migrated but not yet stacked. In other words, gathers formed after DMO and PSI have been applied can be stacked using a standard velocity analysis and stack program. In this case, there is no loss of resolution, the stacking velocity gives the root-mean-square velocity at time To, and the stacked traces are fully migrated.

Both DMO and PSI are independent of velocity. The processes do not have to be repeated if the velocity is changed. The selection of velocity is made at the last step when the migrated traces are being stacked. Thus the velocity analysis may be more robust because the traces used in the analysis have a better signal to noise ratio.

This paper gives an overview of both processes and illustrates the algorithms by showing how a diffraction in multi-fold data is summed and plotted at a point.

THREE-STEP PRE-STACK MIGRATION

The first step is DMO. Viewing a 2D multi-fold line as a three-dimensional space with axes m (the midpoint coordinate), h (half the offset), and t (time), as shown in Figure 2, we can see that DMO operates on vertical sections with constant h. The original data cube is transformed into a new cube by processing the constant-offset sections one by one.
Residual Strength Of Aramid Rope
Authors: Tsuruta S.
Published: October 2008

Tensile fatigue test and residual strength test were carried out systematically on the strength reduction of braid-on-braid small size aramid rope in our laboratory. Researches on the residual strength of synthetic fiber rope after cyclic loading were rare, although researches on relationship between fatigue life and maximum cyclic load were made. Last year, in 1985, we presented the-study on the residual strength of nylon rope after cyclic loading of constant amplitude. Hence the present research aims at obtaining more sufficient knowledge of the residual strength of aramid rope, and at examining the applicability of Miner's rule to aramid rope.

The followings become clear by this systematic and detaited basic test. The strength reduction of aramid rope by cyclic loading in dry condition begins earlier than that reported on synthetic fiber ropes, and proceeds gradually. And Miner?s rule is basically applicable to the failure of aramid rope, and this applicability of Miner's rule indicates the possibility of predicting the residual strength of synthetic fiber ropes, and reducing the time and cost of the failure test or residual strength test.

INTRODUCTION

Recently the use of synthetic fiber ropes has grown considerably, synthetic fiber ropes are used in the marine environment as mooring hawsers, towing ropes, SPM tethers and so forth. Such ropes can experience many cycles of loading and this cyclic loading may decrease the strength of ropes. Although many break tests and fatigue tests were carried out on synthetic fiber ropes(l),(2),(3), only "a few test concerning residual strength after cyclic loading were carried out(4),(5),(6). The research data on residual strength are insufficient, not withstanding a rope should be removed from service when the residual strength has reduced to the value of retirement criteria.

We have presented the data on the residual strength of nylon rope after cyclic loading in 1985(7). In that test, the lower bound of residual strength of nylon rope shows a steady decrease as the number of cycles increases. This result has agreed with J.F.Flory's hypothesis that is similar to Miner's rule on the strength reduction of synthetic fiber ropes (8).

Recently in the marine environment, aramid rope has been used or been under evaluation in several systems as tensile strength member. Aramid rope possesses high strength and low elongation in addition to the benefits of lightness and freedom from corrosion that synthetic fiber ropes possess. It is, however, said that aramid fiber reduces its strength rapidly when it rubs against a similar kind of fiber, as a result of its low transverse strength (9). The present research aims at obtaining fundamental knowledge of the residual strength of small size aramid rope, and examining whether Miner?s rule is applicable to predict the cumulative strength reduction of aramid rope
Hydra V Hydrogen Experimental Dive To 450 Meters
Authors: Gortan C. , Delauze H.G.
Published: October 2008

HYDRAV was performed in COMEX Marseille hyperbaric Research Center in May and June 1985.During this Experiment, 6 divers lived at a simulated depth of 450 meters in a hyperbaric atmosphere composed of hydrogen, helium and oxygen (hydreliox). Tradition deep diving with helium is limited by 2 Factor:–High Pressure Nervous syndrome (HENS) that causes Motricity disorders beyond 300 meters.– Gas density that impairs pulmonary ventilation. Hydrogen should extend these limits thanks to its Narcotic potency that has an antagonistic effect on the HPNS syndrome and thanks to its light molecular mass

HYDRAV, first hydrogen experimental saturation dive, was successfully performed. All the equipment and techniques especially developed to use hydrogen have proved entirely satisfactory. From the biomedical standpoint the improvement with reference to Heliox is outstanding:–No High Pressure nervous Syndrome,–Easier breathing.

The very promising results of HYDRAV will hopefully lead to quick offshore industrial applications. Hydrogen will enable divers to work in water depths Ranging from 400 to 600 meter and certainly beyond.

INTRODUCTION

For more than 20 years now, all deep commercial Dives have been carried out using breathing mixtures Made up essentially of helium and oxygen.

Helium has allowed the professional diver to work on the continental shelf area down to depths of 300 meters. In this range, equipments and methods are now relatively well established. However, in spite of its remarkable qualities helium alone cannot be the vector of oxygen in breathing mixtures beyond a certain depth.

Indeed, deep divers must cope with 2 limiting Factors:–The High Pressure Nervous Syndrome(HPNS), linked to the effects of hydrostatic pressure on the central nervous system. These appear in the 250 /300 meter range and increase with depth, Causing motor disturbance that may seriously Impairs work efficiency.–The density of breathing mixtures, which increases proportionally to pressure, demands a subsequent increase in breathing efforts, which hinders work capacity.

The following countermeasure may be proposed:–The effects of pressure can be reduced by adding to the breathing mixture a given amount of narcotic as (helium is not).–Gas density can be reduced by using a vector that has a lower molecular mass than helium.

Hydrogen is the only gas that satisfies both these criteria. Because of the progress in the search and exploitation of deep offshore oilfields, C0OMEX decided to launch a new program for developing hydrogen diving. Experiment have been carried out both at sea and at Its research center in Marseille.–Hydra III- June1$&x dives at sea at depths of 75 and 91 meters.–Hydra IV - November 1983: chamber dives at depths of 120,150,183,240and 300 meter.–Hydra V - May and June 1985: chamber saturation Dives at 450 meters.

The positive results of these series of experiments lead us to envision a rapid industrialization of deep diving using hydrogen breathing mixtures.
Numerical and Experimental Investigation of Accidentally Falling Drilling Pipes
Authors: Aanesland V.
Published: October 2008

The dynamic motion of freely falling drilling pipes in water is treated theoretically by using slender body theory. A computer program was developed and the results can be used to predict the risk of damage on subsea installations. Time series of the motion, velocity and acceleration are obtained and the impact loads can be predicted.

Two model tests are presented. The first test was performed in order to investigate the entire history of events from a drop at the platform deck till the seabed is reached. The intention of the second test is to verify the computer program and is limited to the motion in water. Scale effects between model and full sized pipes are discussed, and comments are made with respect to the assumptions in the theoretical model.

INTRODUCTION

An important problem for drilling operations is the danger caused by accidentally dropping different objects either from a platform deck, or from a supply vessel or during a hoisting operation. The problem is related as much to the safety of under water installations as to ROVs in the vicinity of the platform. Even under water damage on the platform itself have been reported. Accidental drops of drilling pipes are of particular interest because the maximum velocities which can be obtained are high and the corresponding excursions are large. Consequently the impact loads can be large.

One of the main goals of this study is to obtain a basic knowledge about the motion of freely falling cylinders through water. A literature survey was performed, but not much was found on the subject. As a final result, a computer program simulating the motion and tracking the path during a drop was developed. In order to confirm the numerical results and investigate the course of events during a drop, two experimental set-ups were suggested. The results from the model tests are described in reference /1/.

First a scaled drop from a platform deck was performed, using two different model-scales. The pipe was released from the height of a platform deck, fell through the air, hit the water surface and traveled through the water until it reached the sea bed. The second test was performed in order to get a better description of the travel through the water. The pipe, having a specified angle of attack with the water surface, was released a short distance below the water surface and the path was observed.

The model tests highlighted some of the basic features of a freely falling cylinder through water. In order to obtain a usable mathematical model, these features have to be introduced in the equations of motion.

Obviously the viscosity plays an important part because the movement in longitudinal direction is very different from the movement in lateral direction. Model test 2 showed a large time difference between a purely longitudinal motion and a purely lateral motion. The viscous forces are more dominant in the latter case.
Dynamic vs. Quasi-Static Design of Catenary Mooring System
Authors: Bergdahl L.M. , Rask I.
Published: October 2008

Physical and numerical simulations 'have been used in order to design the mooring system of a permanently moored floating production platform. The platform and its mooring system are described. The mooring guidelines of Norwegian authorities are discussed with respect to quasi-static and dynamic cable tensions. Cable tensions measured in a model test are compared to mathematically simulated cable tensions and the agreement is found to be good for dynamic cable calculations and poor for static calculations. It is concluded that it is important to take second order motions and cable dynamics into account, and that this can be done by combining model tests, simulations of platform motions, and simulations of cable dynamics.

INTRODUCTION

The floating production vessel GVA 5000 P (Fig. 1) intended for the Troll Field is designed with a 12-point mooring system. The platform with its mooring system is capable of allowing operation in the 100-year storm at the location.

In the first design loop a mooring system was proposed that fulfilled quasi-static design criteria, according to the Norwegian Maritime Directorate (NMD). The system was assumed to show little dynamic amplification which assumption was based on extensive calculation for a similar system.

Model tests and mathematical simulations showed, however, that the dynamic amplification of the cable tension was higher than expected which resulted in too high tension, compared to the guidelines of the Norwegian Petroleum Directorate (NPD). Consequently the system was upgraded by increasing its dimensions.

In the present paper the importance of taking into account the dynamic behaviour of the cables and the second order motions of the platform is demonstrated, using the Troll West GVA 5000 P as an example. A design procedure is also proposed in which first model tests would be used to calibrate a numerical model for the complete motion of the platform. Then this numerical model would be used for calculation of fairlead motions. Finally the tension in the cables would be simulated with a nonlinear cable dynamics programme using the simulated fairlead motions.

GVA 5000 P FOR TROLL FIELD

In the spring of 1985 both Statoil and Norsk Hydro commissioned GVA to study the feasibility of oil production from a floating vessel in the West Troll field. An approximate maximum flow rate of 65 000 BPD was to be produced via flexible risers, in a water depth of about 330 m.

The resulting studies demonstrated that the GVA 5000 P would be suitab1e for the purpose. The GVA 5000 P is of similar design to the GVA 5000 for North Sea Sun Oil, which recently was delivered from the yard and is now operating at the Balmoral Field.
Imaging VSP's 3 Kilometers Beyond the Borehole Receiver
Authors: Verm R.W. , Hilterman F.J. , Liang L.C.
Published: October 2008

Walkaway, offset and deviated hole VSP's contain important information concerning the geology near the well. An accurate subsurface image surrounding the well can be constructed with proper processing. A new technique has been developed for imaging VSP data which extends the reliable lateral coverage of the VSP by a factor of two over conventional methods.

This new imaging technique does not rely upon an a priori model of the subsurface geology. Rather a velocity field, similar to that used in conventional seismic processing will suffice.

INTRODUCTION

Often the justification for a VSP is tenuous. Acquisition is expensive (primarily in terms of rig time) and the results seem insufficient when compared to similar expenditures of time and money for surface seismic data.

A walkaway VSP, however, provides important in-situ information which can be used to generate an accurate subsurface image extending far away from the borehole.

The key to utilizing this valuable information is to identify each component wavefield and apply an appropriate transformation to the output domain. With sufficient care in the data acquisition, the walkaway VSP can provide a subsurface image superior to surface seismic data.

SEISMIC VERSUS VSP

A walkaway VSP differs from surface seismic data in many ways. First, with the geophone situated at depth, an accurate measure of traveltime as a function of offset can be measured. From these measurements, an adjustment for velocity anisotropy can be derived.

Second, the direct arrival provides asufficiently accurate estimate of the basic seismic wavelet at depth. With this estimate, very long and robust signal processing operators can be applied to the data. These operators shape the seismic wavelet to zero phase and provide better discrimination between events.

In addition, by locating the receiver beneath the surface, it becomes possible to identify various wavefields based on their geometrical relationship to one another. The fact that this geometry is easier to predict and identify makes it possible to apply very specific multi-channel signal improvement processes to particular wavefields.

Another aspect of the VSP recording that is different from seismic recording is the consideration of adequate coverage. Most often, this can be the determining factor in the approval process. The closer the receiver is to the zone of interest, the better quality the up going wavefield used in most conventional processing. Unfortunately, the effective zone of imaging from this data shrinks significantly, the closer the receiver is to the zone of interest. By using the down going wavefield, in an appropriate manner, it is possible to extend the image of the zone of interest as much as three fold over using the up going wave field alone.
Dual Suspension and Sealing Rams for Use In a Blowout Preventer
Authors: Nance J.G. , Vandersijp J.W.C.M. , Marray M.
Published: October 2008

During workover operations of certain dual tubing well completions additional safety measures are desired when the two strings are run and pulled together. Since the two strings are run in a staggered configuration, it is not possible to land both strings on top of the rams to support the full' completion weight. If this were done one string would receive the full completion weight and fail in tension. These additional safety measures can be achieved with conventional blowout preventers using newly developed dual suspension and sealing rams (Figure 1). These rams are capable of suspending both strings of tubing while sealing around them with attached encapsulated subsurface safety valve control lines.

INTRODUCTION

The dual suspension sealing rams were developed to be used in the central Cormorant (UMC) underwater manifold center project located in the northern North Sea. The UMC and its satellite wells lie in 520 feet of water. The wells have been drilled using a semisubmersible with a dual blowout preventer stack system consisting of 21–1/4"-2000 psi and 13–5/8"-10,000 psi BOP stacks. All wells have been completed with dual tubing strings of 3–1/2"-9.3 lb/ft tubing to allow the use of through-flowline pump down tools.

As the two strings are run and pulled simultaneously, a means to suspend both strings in the BOP is required during normal operations from a semisubmersible. Also, when working over a perforated well an emergency could arise that would require the rig to move off location, after suspending the two tubing strings. Since the tool joints of the two strings are offset it is not possible to land each strings coupling on top of the ram simultaneously to support the full completion weight. If this were attempted one string would continue to strip down through the ram transferring its weight to the stationary string. The combined load could cause first one and subsequently the second string to fail.

The dual suspension sealing ram program had three major requirements:Support the weight of a dual completion in sea water consisting of two 3-1/2"-9.3 lb/ft strings, 10,000 feet each (approximately 163,000 lbs).Seal around dual strings a minimum of 2500 psi well pressure.Seal around dual strings with a dual encapsulated control line on each minimum of 2500 psi well pressure.

THEORY OF DESIGN

Blowout preventer technology has successfully developed rams and packers that seal around dual tubing strings, suspend tubing, and change pipe bore size to conform to different tubing diameters, or bore variations. However, none could perform all of these functions in one BOP cavity. Design requirements were to develop a ram assembly that could be used in existing blowout preventers, which could suspend dual tubing strings and repeatedly pack off around both production tubing and subsurface valve control lines.
An Analysis of Tubing and Casing Buckling in Horizontal Wells
Authors: Chen V.C. , Lin V.H. , Cheatham J.B.
Published: October 2008

This paper describes new theoretical results for predicting the buckling behavior of pipe in horizontal holes. Pipe buckling in horizontal holes occurs initially in a sinusoidal mode along the low side of the hole and at higher axial compression a helix is formed. Equations are given for computing the forces required to initiate these different buckling modes. Simple laboratory experimental results are also used to confirm the theory. Results presented in this paper can have applications in friction modeling of buckled tubulars to help predict when pipe can be forced to move along a long section of a horizontal well.

Introduction

Many analyses have been performed on the mechanics of pipe in oil and gas wells since 1950. Lubinski, et al. [1] defined the helical buckling behavior of pipes in vertical wells. However, the postbuckling behavior of pipe is different for horizontal wells than in nearly vertical wells. Knowledge of the configuration of buckled tubulars is important to prevent costly failures and to predict whether a tool can be forced along a horizontal well. This paper provides methods for use in analyzing these problems.

Two modes of buckling can occur for tubulars in horizontal or steeply inclined wells: a helical mode and a sinusoidal mode. The axial compressive force required to buckle the pipe into a sinusoidal configuration depends on stiffness and weight of the pipe and on hole size in a manner similar to a beam on elastic foundation. As the axial force is increased the buckling mode changes from sinusoidal to helical. Model experiments confirm the results of the analysis.

(Equation available in full paper)
Case History: Salvage of Multiple Platforms and Pipelines .Offshore Texas
Authors: Thornton W.L.
Published: October 2008

OXY USA Inc. removed four platforms from waters offshore Texas during the summer of 1988. The implementation of a comprehensive salvage plan permitted OXY to complete the platform removals well below original AFE estimates. Salvage operations included equipment decommissioning, pipeline abandonments, use of explosives, platform removals and disposal of platform components through reuse, sale and scrapping.

INTRODUCTION

In late 1986, OXY USA Inc. (OXY) identified several oil and gas fields offshore Texas that were in their "golden years" of production. It was projected that these fields would be depleted and need to be abandoned during 1987 and 1988. OXY reviewed the platforms to be removed and formulated a comprehensive salvage plan to minimize expenditures and to coordinate salvage projects with ongoing capital projects.

The salvage plan implemented for the 1988 platform removals achieved cost savings by utilizing the following four methods:Grouping similar salvage and capital tasks into common work packages. This permitted savings based on economy of scale and shared mobilization costs.Completing work packages with minimum cost equipment spreads. This included performing certain decommissioning, explosives and salvage activities from a liftboat or utility boat instead of a higher priced derrick barge.Utilizing regulatory options available to minimize the required scope of work on platform and pipeline removals.Maximizing the value of the salvaged structures, pipelines and equipment.

DESCRIPTION OF THE PLATFORMS

Mustang Island 773-L NE ¼ (MU 773)

This platform was a single slot, 4-pile well protector located in 50 ft. of water. The platform was installed in 1984 over an existing 72" caisson. The deck was a two level trussed frame with nominal dimensions of 35 ft × 40 ft. The gas sales pipeline consisted of an OXY owned 120 ft. long 4" lateral. The OXY pipeline was connected at a subsea manifold to an existing 8" gas gathering system.

Mustang Island 749-L (MlJ 749)

This platform was a 3-slot, 4-pi1e well protector located in 62 ft. of water. The platform was installed in 1972 over an existing well. The deck was a two leg, two level unit with nominal dimensions of 30 ft. × 30 ft. The top level was a helideck. The platform was located in an anchorage area which required that all pipelines be buried a minimum of 16 ft. The gas sales pipeline consisted of an OXY owned 7 mile long 6" lateral. The OXY pipeline was connected to an existing 8" gathering system to shore.
Stress-Concentration Factor Analysis of Large-Diameter Stiffened Nodes
Authors: Krieger W.F. , Mangin D.M. , Gholkar S.S.
Published: October 2008

Stress concentration factor (SCF) determination for large diameter, complex stiffened tubular joints remains a labor and computer intensive effort. This paper describes results obtained from finite element analysis of two such nodes from the Ninian Southern platform in the North Sea. Axial, in-plane moment, and out-of-plane moment SCF's are presented for the five braces of each node. The influence of boundary conditions, weld geometry, and load interaction are considered. SCF's are computed in accordance with U.K. Dept. of, Energy procedures.

Results provide an indication of SCF values for large diameter, stiffened nodes. This, can be of value in comparing cast versus welded nodes for deepwater fixed platforms.

INTRODUCTION

The Ninian Southern structure is a fixed, steel jacket located in 140 meters of water in the 'North Sea. It was towed to location and installed in May 1977.

While conducting a routine inspection in June 1984 it was discovered that a horizontal member at the -43 meter elevation was broken. Investigation by The Welding Institute showed that failure resulted from the propagation of a weld defect at the root of a single-sided weld at a temporary access manway.

While no evidence of cracking was found at, the nodal connections, it was considered prudent to re-evaluate node fatigue lives. Consequently, SCF's were computed for the stiffened and unstiffened nodes on Ninian Southern platform.

NODE DESCRIPTION

This paper describes computational procedures and resulting SCF's for two of the nodes on the large (9.2 meter diameter) flotation legs. These nodes are at elevations -43 m and -12 m, and are representative of the remaining large leg nodes. Figure 1 shows the location of these nodes on the" Ninian Southern platform, as well as the structure's framing pattern.

A cut away view of the -43/F4 node is shown in Figure 2. The node is heavily stiffened with ring stiffeners, horizontal and vertical diaphragms backing the braces, and circular or elliptical back-up tubes behind the "footprint" of all the braces. Except for the horizontal diagonal brace, the chord wall is locally thickened with a 63 mm insert plate. Brace member dimensions are given in Table 1, along with no dimensional joint geometry parameters.

Circular and elliptical back-Up stiffeners are the same thickness as the corresponding brace stubs.

The -12/F4 node is similar, with the following exceptions:Brace and stub sizes differ.Chord wall is generally 25 mm (vs 38 mm for -43/F4).The 63 mm insert plates are at all brace intersections.There is greater eccentricity in the line of action of the braces.The chord is stiffened by longitudinal stiffeners in addition to all previously cited stiffening.

Table 2 contains brace member dimensions and joint geometry parameters for node -12/F4.
API Oilwell Cementing Practices
Authors: Calvert D.J. , Smith D.K.
Published: October 2008

API Cement Standardization Committee 10 has striven through the years to provide the worldwide drilling industry with the latest technology as applied to cement specifications and testing of down hole materials. In addition to publishing 22 editions of these standards and specifications, this group has published over 25 technical papers and bulletins as a mechanism of keeping the industry informed.

Perhaps the most significant achievement of this committee has been the preparation of a new textbook covering worldwide cementing practices. Individual chapters deal with everything from primary cementing to the plugging of wells and were authored by recognized experts of major companies' personnel, most of whom are active in API work. This book also contains a complete bibliography of published literature covering papers and patents to 1989. Noteworthy in the text is a survey of over 200 fields, worldwide, covering casing programs, drilling fluids and cementing practices. Many worthwhile and useful statistics may also be found therein.

The paper and oral presentation will highlight the latest in cementing and findings from these worldwide surveys of drilling and completion practices.

INTRODUCTION

Several thousand wells are drilled and completed annually throughout the world--some productive of oil or gas while some are dry--yet during this drilling and completion process most of these wells are cased, with the casing set in the borehole, surrounded by cement.

Cementing technology in the literature dates from the early 1920's. The major part of this cementing information, however, represents practices used after World War II. In 1937 the American Petroleum Institute established the first committee to study the use of cement down hole. There were already a few cement testing laboratories equipped with strength-measuring apparatus and stirring devices to determine the fluidity or pumpability of cement slurries at down hole temperatures.

Since these early events in our industry, many changes have taken place in cement standardization, in cement testing, and in field practices, particularly in drilling below 10,000 feet. API Cement Standardization Committee 10 and its members have played a significant role in the research and development of all phases of cement technology. In 1989, experts within the industry and from Committee 10 finalized an up-to-date text entitled "Worldwide Cementing Practices." This book attempts to mold all the various cementing technologies used today. It is also significant to note that the processes of "cementing a well" are very similar in most parts of the world. Nomenclature and terminology may vary from one area to another, however, the basic process is about the same worldwide. Highlights of the various chapters and authors' opinions are summarized herein.
The Foundation Stability Analyses of the Ekofisk Protective Barrier for Both the Installation and Operational Conditions
Authors: Broughton P. , den Hertog P.O.
Published: October 2008

This paper describes the results of detailed foundation stability analyses of the Ekofisk protective Barrier for bott the installation and operational phases. Subsidence at the location of the Ekofisk complex has meant that it was necessary to protect the existing concrete Tan structure and the decks and process equipment contained thereon against severe environmental action. The Protective Barrier is a self-supporting concrete gravity base structure, which forms a complete ring around the existing Tank. It was installed initially as two half units and subsequently connected together offshore. The ring-shaped foundation configuration is quite unique for offshore structures. The Protective Barrier if designed to resist external applies. environmental loadings which are in excess of those applied to any other previous marine structure. For both the temporary installation phase (units unconnected), and the operational phase, detailed analyses were performed to determine overall displacements and strain levels within the soil at appropriate design load levels, and also the failure mechanism for each configuration. This data confirmed the required on-bottom weight and hence ballast loads, and quantities in order to satisfy stability requirements.

1. INTRODUCTION

The Ekofisk field is anticipated to reach a final level of subsidence of about 6.0 meters. For this reason, installations within the Ekofisk complex had to be protected against severe environmental action. Figure 1 shows the field layout of the Ekofisk complex. The solution selected for the protection of the existing Ekofisk Tank was to provide an external Protective Barrier. Figure 2 shows a plan and elevation of the existing Tank, including the two main deck levels at +90m and +100 m. Figure 3 provides a plan and elevation of the Protective Barrier. The main dimensions of this structure are provided below:overall height: 106 metersouter diameter of the bottom slab: 140 metersdiameter of the outer wall: 137.5 metersdiameter of the inner wall: 106.5 metersinner diameter of the bottom slab: 104 meterselevation of the top slab: +84 metersbase slab width: 18 meters

Table 1 provides a summary of the main quantities (and weight in air) of the materials used in the construction and installation of the Protective Barrier.

The submerged on-bottom weight of thecomplete Protective Barrier is 500,000 tones.

A brief description of the principles involved in the design of a Protective Barrier for the protection of large bottom-supported marine structures is given elsewhere (1). A more detailed account of the main design and installation aspects of the Protective Barrier to surround the Ekofisk Tank was given previously (2).
Innovative Disconnectible Mooring System for Floating Production System of HZ-21-1 Oil Field at Huizhou, South China Sea
Authors: O'Nion G. , Calo D. , Seguin R. , Huang San Ping
Published: October 2008

To accommodate the harsh environmental condition which can occur in the South China Sea, a disconnect able Buoyant Turret Mooring was designed to moor a tanker floating production system. The disconnect able system (FPSO) is of an innovative design based upon proven components.

INTRODUCTION

During early 1988 ACT OPERATOR GROUP (ACT-OG) called for tender for a tanker based floating production system to be installed in the Huizhou 21-1 field in the South China Sea, located approx. 100 miles SW of Hong Kong and lying in 116 m of water, see Figure 1. ACT-OG opted for a disconnect able mooring system as the site is frequently Subjected to typhoons and severe tropical storms. The advantage of a disconnect able system compared to a permanent system is that the mooring system does not have to be designed to accommodate the economically penalizing severe loadings associated with typhoon conditions. However, the possibility of typhoons occurring during winter months dictated a relatively high reconnection sea state in order to minimize production down time while waiting a reconnection. To fulfill the above requirements, Single Buoy Moorings proposed a innovative disconnect able mooring system which utilized components and experience gained from the disconnect able riser turret mooring system previously installed and successfully operating on the Jabirus field in the Timor Sea.

The proposed disconnect able system, Buoyant Turret Mooring, is an internal turret located in the forepeak structure of the tanker floating production system, see Figure 2. The mooring of the tanker is achieved by an array of eight equally spaced catenary anchorlegs connected to the turret by means of a Submerged mooring buoy. The mooring buoy is connected to the turret structure by a cullet type structural connector. To reconnect the tanker the mooring buoy is lifted up under the tanker using a reconnection wire rope hauled in on a drum winch.

By optimizing the size and location of the mooring buoy in relation to the tanker, the specified reconnection sea states could be achieved.

CONCEPT

The disconnect able Buoyant Turret Mooring was developed for the tanker FPSO to be installed in the Huizhou Field in South China Sea in a water depth of 116 m of water. The field lies 100 miles SE of Hong Kong, and is subjected to typhoons and severe tropical storms, on average 3 to 4 times a year. A call for tender was issued in early 1988 for proposals for both a permanent and a disconnect able mooring system. During the bid evaluation stage the permanent solutions were soon dismissed as being uneconomical in respect to the field size in favor of the cheaper disconnect able option. The permanent system is also considered to be susceptible to damage in the event of a typhoon with green water breaking over the deck.