bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seal Integrity and Connector Clamping Force at the Subsea Wellhead
Authors: Owens J.H. 
Published: October 2008

ABSTRACT
The importance of the relative stiffness of the hydraulic connector and the wellhead hub for subsea wellhead connections is demonstrated using existing design principles for bolted flanges and clamps. Connector stiffness is determined experimentally for one design, and a method utilizing finite element analysis is demonstrated for another. A 3-D finite element model is used to determine wellhead seal radial loading after hub separation has occurred on one side of the hub interface, as it might under a severe moment. The results suggest that the normal load between hub seal pocket and seal OD reduces markedly as the gap increases, and more of the internal pressure loading on the seal is resisted by hoop stresses in the seal itself. However, even at a gap of 0.090 inches, the loading on the seal appears to be uniform around the seal pocket. At a hub separation 0.090 to 0.120 inches, all OD normal load is lost on a portion of the seal near the separation.

INTRODUCTION
In a drilling operation, the connection between the blowout preventer stack, with the lower marine riser package and riser above it, and the wellhead near the sea floor must be made remotely, often at great sea depths. It must be well pressure tight under relatively severe bending, shear and tensile loads. A heavy, steel, pressure energized seal is used, and the joint is made up using a hydraulic clamping device, a marine hydraulic connector, which preloads the seal and generates a heavy, axial compression between the hub faces of the joint. The load, referred to as the connector clamping force, is generated primarily to ensure that the hubs do not separate and move relative to each other under external loads, thus chafing the seal, wearing it out, and eventually causing a leak.
That connector clamping force is important for maintaining joint and seal integrity is well established by field experience. Connector clamping force and its high sensitivity to sliding friction on working surfaces are discussed in a previous work by the author [1]. Substantial theoretical and experimental work regarding hub separation and stresses for API clamp connections has been done by [2].
In what follows, the interaction of the three principal parts which make up the subsea wellhead connection, seal, hub, and connector is considered. First, the importance of the relative stiffness of the connector and hub is explained using basic design principles usually applied to flange connections. Second, the stiffness of an existing hydraulic connector design is measured experimentally, and then finite element analysis is used to determine how the connector-hub stiffness ratio affects the magnitude of the external tensile force required to cause hub separation.
Lastly, the interaction between the steel wellhead seal and the hub seal pocket is investigated when an external moment separates the hub faces on one side.
Offshore Sand and Gravel Mining
Authors: Padan J.W. 
Published: October 2008

ABSTRACT
This paper reviews the status of mining offshore for sand and gravel on a world-wide basis. It discusses the technology for exploration and evaluation of sea floor mineral targets, as well as mining, transportation, and processing. Large operations in Japan and Europe are described, based upon personal observations of the author. The U.S. situation is outlined and opinions offered as to the outlook for the future.

INTRODUCTION
Sand and gravel are broad terms used to cover almost any ground rock or mineral. Size distribution and performance specifications are more important that mineralogy per se but quartz is the most common constituent. Sand, of different size bands, ranges from 0.06 to 2 mm diameter: gravel from 2 to 8 mm.
Sand and gravel together comprise a low unit value mineral commodity (--$2.55 per metric ton in the U.S. in 1982) that is used in nearly every country in the world for construction aggregate and fill. This commodity is mined from the seafloor in several areas of the world for those same purposes and, in addition, for the restoration of stormeroded beaches.
Commercially important marine sand and gravel occurs as beds and lenses of unconsolidated aggregate, generally Pleistocene or younger, lying at or near the surface of the continental shelf under 20 to 30 meters of water. Glacial deposits are common in Northern latitudes; submerged beach and river deposits are mined elsewhere. Aragonite "sand", precipated from seawater, is mined in The Bahamas for construction aggregate as well as for use in the glass industry.

INDUSTRIAL OPERATIONS
Deposits currently mined offshore occur where favorable marine geology, metropolitan (not necessarily coastal) markets, navigable water, and a favorable legal regime occur in juxtaposition. The two largest industries have developed in Japan and Northern Europe. Each is discussed blow.

Japan
Rapid depletion of onshore deposits of construction aggregate has caused Japan to tap sand deposits in coastal waters. In recent years a fleet of about 900 small vessels has recovered 15 to 20% of all aggregate mined in Japan. Most of the mining is for sand for use as fine aggregate, which is costly to grind from crushed rock. Coarse aggregate is supplied increasingly by crushing rock. Annual production is 60 to 70 million tons and is expected to increase. By way of comparison, this rate of mining is double the rate of mining off Northern Europe although the latter operations have received more attention in the Western literature.
Most of the mining occurs off Western Japan, as shown in Figure 1. About two-thirds of the production comes from the Seto Inland Sea; most of the remainder comes from the north coast of Kyushu, off Fukuoka. In general, the seafloor upplies western Japan while eastern Japan is relatively uncrowded and so is able to utilize on land deposits of sand and gravel. Tokyo's huge demand is satisfied from onshore because of its great distance from marine deposits.
Comprehensive Dynamic Analysis of Offshore Loading Concepts
Authors: Natvig B.J. , Berta Marco 
Published: October 2008

ABSTRACT
A computer based metod for comprehensive analysis of Offshore Loading concepts is discussed. The method differs from much of the previous published work in that all of the following effects are accounted for:Non-linear time domain analysis in irregular seas.The frequency dependent added mass and potential damping are tackled by convolution integrals.Still water damping, wave damping and current damping have been included in accordance with advice given from NSMB, WageningenTwo tankers, connected by a non-linear hawser, may be moored in tandem.The moored tanker is modelled using all 6 degrees of freedom.Slowly varying wave drift and non-constant wind forces wrt. the instantaneous ship headings are included.Non-linear inertia forces, as they appear in the ship manoeuvering equations, are included.Weather vaning stiffness due to wind and current are included. The way the computer program is organized to account for any types of mooring is a special feature of this program. Examples of different mooring applications are given in the paper.

INTRODUCTION
Exploration for hydrocarbons in the waters outside Northern Norway was started 3 years ago and the prospects now are promising. A major research programme to prepare for the many complicated problems yet to be tackled in this environmentally difficult area was started in 1980 by Statoil and several other oil companies. Amongst the larger of the over 20 research projects thus started are two projects for. Offshore Storage and Loading in 350 meters of water. These two projects are sponsored by Statoil and Agip and the project execution is shared between Aker Engineering - Oslo and Tecnomare - Venezia. In the first project several existing and proposed Offshore Storage and Loading concepts are evaluated for merits and capabilities. The second project concerns the further development of the most promising concepts.
The need to evaluate several different storage and loading concepts in an unified manner necessitated a more general analysis tool than was readily available. The decision was therefore made that such a computer based system were to be developed as part of these projects. An early version of this program, which is called Sea Off Load, is now running. A feature of the program is that it is structured in such a way that it will allow for the insertion of any mooring system that may be required. This will result in a family of programs which will have the description of the environment, the basic ship formulation, the assembly and solution of the equations of motion all in common. A block diagram of the structure of Sea OffLoad is shown in figure 1. At the present time, the modelling of a catenary moored large volume storage buoy together with an off take tanker is being formulated. For this configuration, which is only mentioned in passing, the storage buoy is substituted for the moored tanker.
Diffractions Reveal Drilling Hazards
Authors: Fulton T.K. , Hsiao R.T. 
Published: October 2008

ABSTRACT

1983 OTC PAPER 4507

DIFFRACTIONS REVEAL DRILLING HAZARDS
Seismic waves are diffracted where there is a sudden change of curvature or acoustic impedance along a surface such as boulders embedded in clay, across faults, the eroded edges of channels, and at the edges of shallow gas drilling hazards. Diffractions reveal these situations, especially if they are enhanced at the expense of reflections and refractions and organized as in an Offset Panel. The Offset Panel was introduced by FuIton and Darr (1981) as a powerful too I for the analysis of seismic data. Their paper described a method by which conventional exploration seismic data are used to detect shallow gas drilling hazards.
The work of Berryhill indicates that boulders, which are one-half the dominant wavelength in size, can be expected to generate diffractions. Hazard seismic data from the North Sea presented here show energy in the 500-700 Hertz band corresponding to wavelengths of II to 8 feet. Unfortunately, the spacial sampling of the hazard data is four wavelengths, much too great to resolve boulders. A spacial sampling of 2 to 3 feet would be more appropriate for these data anday allow for the detection of individual boulders or zones containing fewer boulders.
Experience with the Offset Panel to detect shallow gas drilling hazards along the line of the profile suggested the Diffraction Panel to detect gas hazards nearby. In this report we demonstrate the use of the Diffraction Panel to detect buried channels and shallow gas drilling hazards.

INTRODUCTION
This paper deals with engineering and drilling hazards, such as:"Boulder beds" that might alter the design of both offshore structures and their piles.Near-seafloor gassy mud whose shear strength and velocity decrease as the amount of free gas in the mud is increased.Channels and/or near-sea floor faults that may alter the relative strength of the ocean floor.Boulder beds that may be costly in rig time required to penetrate them." Over pressured " shallow gas or shallow faulting which may vent deeper gas. All of the above hazards show a velocity contrast with respect to adjacent strata. Diffracted seismic waves occur at these velocity contrasts and are commonly called diffractions. The scattering of seismic energy may also occur at these contrasts. The subject of diffracted and scattered waves is complex. The events themselves have a dip different from that of reflections. A primary objective of this paper is to demonstrate that a simple display can aid their analysis.
Diffractions can best be observed in common offset profiles. They may be enhanced on a number of common offset profiles arranged in an "Offset Panel" format forease of interpretation.
The Offset Panel display was described as a powerful analysis tool by Fulton and Darr (1981). The display simply arranges common offset profiles vertically by offset and horizontally by Common Depth Point. This arrangement forces reciprocal source and receiver effects to form predictable patterns.
North Sea Physical Model Construction, Data Acquisition, and Interpretation
Authors: Nelson H.R. 
Published: October 2008

ABSTRACT
This paper describes the building, data acquisition and interpretation of a complex physical model, SALNOR, built to illustrate a "typical" complicated N6rth Sea geological structural sequence. The model was built as a proprietary project for statoil who then released it to the Allied Geophysical Laboratories (AGL). The model consists of seven layers that represent the Top Palcocene, Top Cretaceous, J-Uniformity, Top Brent, Base Brent, Top Stratfjord, and Base Statfjord. The respective model material used were 3120 (red), 184 (clear), 3110 (white), 3120, 3110, 3120; and 3110 RTV silicone rubber to represent pre-cretaceous rocks.
The steps required to build the model are detailed, along with photographs of the model as construction progressed. The 3D data set across the model consisted of 240 traces on 240 lines. Several other data sets across this model have since been collected. In order to graphically illustrate the complex structure, the model was cut into 16 square blocks. "Wells" were also core-d in the center of each of these 16 blocks. This allows the seismic data to be directly tied to the reflection sources. It is interesting that when data was collected across the reassembled blocks, there was not excessive diffraction noise created by the vertical cuts and holes.
The initial interpretation was done on paper sections. Later the raw data and 3D migrated data were evaluated using the interactive interpretation capabilities of the Adage vector refresh graphics system. The interactive computer graphics interpretation is illustrated with a 16 mm movie. The movie specifically illustrates the value of rapidly animation through a sequence of vertical, horizontal or mixed vertical and horizontal seismic sections. The movement brings "alive" the geologic structures and stratigraphic sequences and allows the interpreter to make a rapid evaluation of the best prospects.
The model data can be used to evaluate and to teach different interpretation techniques. However the real value is the demonstrated ability of physical model data to accurately represent a complex offshore geological problem, and in the confidence this brings to marine seismic data acquired, processed, and interpreted in a parallel fashion.

INTRODUCTION
In late 1981 Ingebret Gausland from Statoil requested SAL to devise a workshop on 3D interpretation methods that interpreters working in the North Sea would find applicable to their work. It was decided that the best procedure would be to build a model that represented typical North Sea geology and structure and to base the workshop on it. 1 From this basic concept, the SALNOR model was designed. Figure 1 is a contour map of the only horizon that was contoured, the J-Unconformity. The two layers above this were to be flat, and the layers underneath of constant thickness dipping and parallel to each other within each separate fault block. Slight deviations from the planned dimensions occurred during construction and introduced an added degree of realism.
Tieback Requirements for Early Production Systems
Authors: DaMota A.C. 
Published: October 2008

ABSTRACT
The idea of drilling subsea wells, installing a wellhead jacket and tying back to surface is very attractive since it can lead to early production capability.
However, conventional tieback systems are not suitable, when a production platform and/or a second intervention of a drilling rig is required to carry out the tieback.

INTRODUCTION
Early production systems are quite new in the North Sea. Shell Expro considered it for the first time in early '77 for the Fulmar Field where, before installing the main production platform in Summer, '80, a wellhead jacket was launched during the Summer of '79 over a modular template. This template was designed and manufactured in 3 months (March/June '77) although it was not landed until '78 with the help of a Semi Submersible. The same rig ("ocean voyager") drilled the first three wells before being released to allow jacket installation.
A jack up rig (Dyvi Beta) drilled a 4th well shortly after and tied back and completed the remaining wells in the Summer of 1980. The design and execution of these tie backs to subsea wellheads served to highlight not only the drawbacks of the dual BOP stacks, i.e. 20 3/4" X 13 5/8" subsea systems, but also the problem of misalignment.
Similarly the experience gained during the design of the S.E. Auk template for tie back or subsea completion of a single stack subsea system was more enlightening as a wider range of suppliers became involved.
Unfortunately the well was dry ... In this case, again tie back to subsea wellheads was considered and the main lesson learnt was the need for multipurpose subsea wellheads.
Early '81 a similar project was considered, this time for Leman E mudline suspension system tie back. Once more suppliers gave of their best.
This paper reflects the Subjects discussed, i.e. conventional systems (mud line suspension and platform tiebacks) the comments made and suggests different approaches to solve the problem of tying back predrilled wells.
Aware of potential problems posed by tiebacks, several operators (Agip, Amoco,B.P. Esso Norway, Marathon, Montedison, Norsk Hydro, Petrobras Philips and Statoil) met with Shell to discuss lessons learnt from past operations.

CONVENTIONAL MUD LINE SUSPENSION SYSTEMS

Application
Primarily they were designed to reduce weights at deck level on free standing connectors and to speed up the abandonment. Secondarily the possibility of suspension and re-use was envisaged. Both subsea or platform completions were considered. For the latter tieback to surface of subsea strings was required.
Tarsiut Winter Alert Monitoring
Authors: Wright B.D. , Weaver J.S. 
Published: October 2008

ABSTRACT
Tarsiut Island is the first caisson retained island that has been built for drilling operations in the Arctic Offshore. Because of its novelty, a real time monitoring program involving the predicted and observed performance of the island under ice loading was established to ensure safe and efficientdri11ing operations and to satisfy government requirements.
To accomplish this program, an extensive state of the art instrumentation, data acquisition and monitoring system was developed and utilized to collect ice action and island response information. The data was used in real time to assess island stability and provide an alert warning to drilling personnel. The alert levels were related to drilling activities to ensure the integrity of the operation.
This paper describes the methodology, procedures and experiences associated with the Tarsiut winter monitoring program.

INTRODUCTION
Although many artificial islands have been built in the Canadian Beaufort Sea (De Jong and Bruce, 1978), the Tarsiut structure represents a significant new extension to Arctic drilling technology. This island, constructed by Canadian Marine Drilling under contract to Gulf Canada Resources, was the first caisson retained island used for exploratory drilling in ice infested waters (Stenning and Fitzpatrick, 1983). During the winter, spring and summer of 1982, Gulf Canada as operator for the Tarsiut group*, dri11ed the Tarsiut N-44 and N-44A wells from the island as a part of its Beaufort Sea exploration program. The N-44 well, drilled on the same geological structure as the Tarsiut A-25 discovery of 1980, yielded 556 m / day (3500 bbl /day) while the subsequent N-44A delineation well, side tracked from the same well bore, was less prolific yielding 346 m3/day (2175 bbls/day).
In addition to the novel use of caisson technology to reduce the fill requirements for island construction, the Tarsiut structure was located in 21 m of water making it the deepest artificial island ever built in the Beaufort Sea. The island was al so located in an area where dynamic ice motion was expected for at least part of the winter season.
Tarsiut was designed on the basis of theoretical analyses, model tests and full scale experience at other islands (Croasdale and Marcellus, 1978). The design work indicated that under expected ice conditions and loadings, there should be no hazard to the island from the stability or operational viewpoint. However, because Tarsiut was novel, there was a finite probability that the ice conditions might be different than expected or that some interactions not predicted by experience, theory or model tests might occur. This was recognized by Gulf Canada, its partners and the Canadian regulatory agencies and procedures were implemented to ensure that the effects of the ice environment on the stability and operations from Tarsiut Island were known or could be anticipated at all times.
Acquisition and Processing of Gulf Coast VSP Data
Authors: Landgren K.M. , Grubb Karel 
Published: October 2008

ABSTRACT
This paper describes the acquisition and processing of vertical seismic profile (VSP) data from the Gulf of Mexico, including details of an integrated logging/seismic acquisition system. Standard field techniques and typical processing parameters are discussed, and a real data set is used to review the steps in VSP processing. Wellsite processing of field data is also presented.

INTRODUCTION
Vertical seismic profiles are an outgrowth of seismic velocity surveys. Originated in the 1950's, they were developed in the Soviet Union during the two following decades. I In recent years, the awareness and popularity of VSP techniques have spread to the West. Today, developmental activity is underway in all phases of VSP technology: acquisition, processing, and interpretation. As a high-resolution seismic method, vertical seismic profiling is assured of a prominent role in hydrocarbon exploration.
Acquisition of VSP data in the offshore environment requires a marine seismic source, a downhole sensor, surface instrumentation, and a wireline for sensor positioning and signal transmission. Historically, borehole seismic surveys have been performed in conjunction with open hole logging surveys, using the logging wireline interfaced with stand-alone seismic acquisition equipment. The introduction of a computerized logging system, designed for the digitization and taping of borehole logging data, opened the way for the development of an integrated surface system for the acquisition of both logging and seismic data. Such a system was developed, and it was first introduced in the Gulf of Mexico in 1981.

ACQUISITION
A typical setup for well seismic data acquisition is shown in figure 1. The well logging unit is usually mounted on the drilling rig. A downhole sensor and a marine seismic source and sensor complete the necessary acquisition equipment.
The standard seismic source in the Gulf of Mexico is the air gun (figure 2). As an impulse source, the air gun provides adequate energy and the bandwidth necessary for data acquisition. Its signature is complicated by the bubble effect, which results in oscillations with a period of about 100 ms. Frequently, a kit is used which limits the bubble effect, at the expense of reducing the effective chamber size and thus the radiated energy. Another approach to signature improvement is the use of arrays of guns with different volumes. Gun arrays display both reduced bubble effect and increased radiated energy. A hydrophone is used to monitor source signature.
Having produced a pulse of seismic energy, it is necessary to detect the pulse after a series of transmissions and reflections through the earth. The sensor for the work described in this paper consists of a uniaxial stack of four Geospace HS-1 geophones and associated electronics mounted in a downhole tool. During acquisition, the tool is coupled to the formation by an arm under springtension. The tool is designed to operate in well environments normally encountered in the Gulf of Mexico (figure 3).