bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atlantis-II-Deep's Metal Reserves and Their Evaluation
Authors: Guney M. , Nawab Z. , Marhoun M.A. 
Published: October 2008

ABSTRACT
The Atlantis-II-Deep's metalliferous sediments were recently discovered along the mid-ocean ridge system extending into the Red Sea, at a mean water depth of 2,200 m. The average thickness is 7 to 11 m in different sub-basins. The metal-bearing mud contains sulfides of zinc, cupper and iron with significant amounts of silver, gold and cobalt. A variety of oxide, siliceous and carbonaceous gangue minerals are also present.
To determine the in-situ characteristics pertaining to the variability of the metal grades and mineralized thickness, and to study the natural phenomena, mining geostatistics was applied to estimate the Red Sea offshore mineral resources. Horizontal experimental variograms were computed along 0±180 degrees and then models were fitted to analyse the mineralization in each area. Kriging estimates indicate that 696.330 million tons of bulk sediments contain 1.891 million tons of zinc, 0.425 million tons of copper and 3.75 thousand tons of silver. Gold and cobalt contents were calculated from the analysis of solids in flotation concentrates as 47 tons and 5,368 tons respectively.
The significant outcome of implementing geostatistics to the Red Sea brine preciptates is not only for the evaluation of metal reserves, but it also provides a useful tool in the optimization of selective dredging of appropriate areas to be mined.

INTRODUCTION
The Atlantis-II-Deep is a unique marine deposit with a 2,200 m-thick sea water overburden. The stratified muds consist of varying quantities of very fine grained oxides, silicates and sulfides of zinc, copper and iron, and considerable concentrations of gold and cobalt. Extensive systematic exploration has revealed the fact that brine precipitates formed this potentially mineable orebody of economic interest.
The resource potential and economic worth of the Atlantis-II-Deep has been studied at different times utilizing data provided by exploration campaigns. The following are those worthy of mention.
In 1969, Bischoff and Manheim (1) assessed the in-situ value of the deposit at $2.5 billion, based on 41 analyses from 7 piston core samples that were collected during the Chain cruise. This represents:2.9 x106 tons of zinc,1.06x106 tons of copper,8.0 x104 tons of lead,4.5 x103 tons of silver, and4.5 x10 tons of gold. In 1969, the Wando River cruise yielded channel samples from 28 stations within the Hackett and Bischoff (2)in 1973 calculated the estimates and amount of valuable metals in ore on the dry-salt-free material as:32.7 x105 tons of Zn at a grade of 3.48 x103 g/m38.2 x105 tons of Cu at a grade of 0.869xl03 g/m384.01x107m3 of sediment volume. This amounted to a total value of $ 2.33 billion for in-situ resources at the 1972 market metal prices.2.4 x106 tons of zinc,0.5 x106 tons of copper, and8.6 x103 tons of silver. The economic value at this time reached $ 4.2 billion.
In 1977/1978 and 1979, Meseda 1 cruise of Sonne and Meseda 2 cruise of Valdivia were undertaken to obtain an additional 195 statistically distributed core samples.
Suitability of Tankers for Floating Production Systems in Hostile Environments
Authors: Key J.W. , Shumaker F.E. , McClure Alan C. 
Published: October 2008

ABSTRACT
This paper discusses the advantages and disadvantages of semisubmersibles and large tankers (150,000 to 250,000 DWT) when used as floating production and storage systems. Primary technical considerations which are discussed include:Mooring LoadsProduction RisersVessel MotionsCrude Storage and OffloadingSystem ReliabilityField Shut-In ParametersCapital ExpendituresLead Times
The data included is based on computer simulation, model tests, and industry successes in meeting similar challenges.

INTRODUCTION
In the past decade several fields have been produced in the North Sea with semi submersible drilling units which were converted to production units. As a result of the proven suitability of semi submersible production units in hostile environments (Argyle & Buchan Fields), many people believe that only semi submersibles are suitable for those locations. With the increasing use of converted tankers as floating production, storage and offloading units, it is appropriate to evaluate their suitability for more hostile environments.

SYSTEMS EVALUATED
Five basic configurations which are considered in this paper are:Converted Semi; Shuttle Tanker. This includes a semisubmersible drilling unit (modified with production equipment), with continual offloading to dedicated shuttle tankers.Converted Semi; Storage Tanker. This includes a semi submersible drilling unit (modified with production equipment), a permanently moored storage tanker, and periodic offloading with shuttle tankers.Custom Semi Production and Storage. This includes special design and construction of a large semisubmersible, with periodic offloading with shuttle tankers.Production and Storage Tanker; SPM. This includes a very large crude carrier (VLCC), or a converted tanker (150,000 to 250,000 DWT), permanently moored with an articulated tower or single anchor 1eg mooring (SALM) with a rigid yoke, and periodic offloading with shuttle tankers.Production and Storage Tanker; Turret Mooring. This includes a converter a tanker or VLCC permanently moored with a turret mooring system, and periodic offloading with shuttle tankers.
For each case, it was assumed that major pipe1ines are not in place, necessitating the use of shuttle tankers.

MOORING LOADS
Typical mooring loads (without shuttle tanker attached) are shown on Figure 1. The mooring forces are significantly lower for the tanker based unit which weathervanes than for a semi submersible exposed to beam seas. Therefore, a much greater factor of safety can be maintained with similar mooring systems, or the size of the tanker-based mooring can be reduced in order to minimize capital expenditures. The mooring loads for the tanker may be slightly larger than shown when the wind, waves and currents are not collinear.
Acoustic Tracking of Towed Bodies
Authors: Neudorfer M.L. 
Published: October 2008

I. ABSTRACT
Results of tests are presented that show that a simple mechanically fixed mount ultra short-baseline transducer array can be successfully used to acoustically track deep and near-surface towed bodies. An in-water calibration procedure that reduces errors due to transducer array assembly system installation and sound velocity variations is also discussed.

II. INTRODUCTION
The use of ultra-short baseline acoustic systems is common in survey applications for tracking towed bodies. These applications include tracking of deep-towed seismic towfish and near-surface seismic streamers and airgun floats. A common requirement of these applications is accurate determination of a towed body position in geographical coordinates.
This paper describes the results of two tests of an ultra-short baseline acoustic system featuring a fixed-mount transducer array1. The transducer array features wide-beam elements that constantly monitor the entire 360 degrees of the acoustic field. The array is most sensitive in the downward direction but it has sufficient sensitivity at near horizontal angles to perform well in towed body applications. The array's elements are arranged in a perpendicular pattern that enables the system to calculate the three dimensional position of an acoustic transponder.
Near-surface tows were conducted in Puget Sound, Washington and deep tows were conducted in Hogs Fjord, Norway. Accuracy and range performance during these tests is presented and analyzed in this paper.
This paper also describes the steps taken to achieve best accuracy. An in-water calibration procedure that will reduce errors due to transducer array assembly, system installation, and sound velocity variations is also presented.

III. NEAR-SURFACE TESTS
Near-surface tow tests were conducted in Puget Sound, Washington. The transponders used 22 and 24 kHz pulses of 1.33 ms duration. The source level was 190 dB//1 microPascal at 1meter.
A towed beacon was tracked out to a maximum range of 365 meters at a depth of 13 meters in sea state 1 to 2 conditions. With the beacon lowered to 60 meters, a range of 1500 meters was achieved. Tow speeds ranged from 4 to 6 knots.
Tilting the transducer array up 25 degrees so that its sensitive axis would point more closely at the transponder did not increase the achievable range. This result agrees with the general rule that in near horizontal acoustic transmission the achievable range is limited by environmental conditions (usually acoustic ray bending due to thermal variation).
This environmental constraint was observed again when, in sea state 5 to 6 conditions, the transponder had to be lowered to 36 meters to achieve the 365 meter range achieved at 13 meter depth in calmer seas.
Some Recent Applications of Reliability Theory in Offshore Structural Engineering
Authors: Edwards G. 
Published: October 2008

ABSTRACT
This paper describes some recent applications of reliability theory in offshore structural engineering.
In two of the applications, concerning a) a gas riser and b) the steel deck beams of an offshore structure, probabilistic fracture mechanics calculations have been used to investigate safety levels associated with crack-like weld defects and hence give guidance in operational decision-making situations.
In the third application, modern ideas in Bayesian statistics have been used to treat an increasingly common problem - that of developing a fatigue design (S-N) curve from a very limited amount of test data. The Bayesian S-N curve can be used as a design criterion in its own right or as a means of assessing the benefits of performing more experimental work.
Overall, the applications illustrate that probabilistic structural reliability theory has progressed to a stage where it can provide valuable information in real operational situations - provide that appropriate data and analysis capabilities are available. When data are scarce, the advantage of adopting the Bayesian approach to probability theory is also clearly illustrated.

INTRODUCTION
In recent years, important advances have been made in the development of probabilistic structural Reliability Analysis (PSRA) techniques for use in offshore engineeringl,2. Basically, PSRA employs probability theory and statistics to treat the uncertainties in all stochastic variables governing structural behaviour in an explicit manner. In this way, a notional 'probability of failure' can be calculated for the structure or component of interest during a specified time period, usually the service life. This failure probability is recognised as being a more rational measure of safety than the traditional 'safety factor', which has been used for many years in design.
This paper summarises some recent applications of PSRA in offshore engineering. In two cases concerning a) a gas riser and b) the steel deck beams of an offshore platform, probabilistic fracture mechanics calculations have been used to investigate safety levels associated with crack-like weld defects. In the other application, Bayesian statistical theory has been employed to establish a fatigue design curve from a very limited amount of test data.
Since the applications described make use of both classical and Bayesian forms of statistical inference, some background information on these two topics will be given first.

DIFFERENT VIEWS OF PROBABILITY AND STATISTICS
Recent developments in many areas of statistical application - including PSRA - demand a sound understanding of the different views of probability theory and statistics which can be adopted. Broadly, there are two schools of thought (i) the classical (frequentist) school and (ii) the Bayesian (subjective) school.
Recording Technologies for High-Rate Marine Seismic Data
Authors: Aarnaes E. , Sidlowski D.G. 
Published: October 2008

ABSTRACT
Developments in marine seismic data acquisition technology have made available streamer systems with 1000 channels and high sampling frequency. The resulting data rates and volumes are above the capacity of the current magnetic tape recording systems. The recording requirements of high rate seismic systems could be met through developments in laser disc technology, in the area of magnetic tape systems or through online pre-processors reducing the amount of data. New recording technologies are essential for the feasibility of high rate seismic systems.

INTRODUCTION
Industry demand for increased resolution of offshore seismic surveys has resulted in development of more sophisticated acquisition systems. Digital streamers have made possible significant increases in spatial and temporal sampling rates. Some streamer systems provide the possibility of recording up to 1000 channels in addition to high temporal sampling rates. These developments have led to significantly higher data rates than common in marine seismic data recording today.
Standard computer readable magnetic tape, which is well known to the seismic industry, is still the state-of-the-art medium for recording of seismic data. Even though this technology has remained essentially the same for several years, it has so far proved to be reliable and sufficient. Unchanged, however~ it will not be adequate for the kind of high rate seismic data recording indicated above. Implementation of new recording technologies is therefore essential to the feasibility and cost effectiveness of high rate seismic acquisition systems
The increased recording density and speed requirements of high rate acquisition systems can be met in several ways; through new developments in laser disc technology, in magnetic computer tape technology resulting in magnetic tape systems with higher data rate and density, or through the use of high density digital recorders to seismic data acquisition. Another attractive alternative is to use online pre-processors to perform data reduction to match the recorded data volume to the capabilities of current magnetic tape systems. However, online pre-processing is a large subject which we will leave out of this paper.
In this paper we will discuss the use of these recording systems for high rate seismic recording and the status of their development. However, we will begin with a review of some geophysical and operational reasons for using high rate seismic recording.

SOME GEOPHYSICAL ASPECTS.
Increasing production and development costs of off-shore oil fields have forced many oil companies into careful evaluation of new fields and reevaluation of existing fields currently in production. To meet the required data quality may in some areas require fine spatial sampling intervals of the seismic data, in some cases significantly less than 10 m. The Delphi Survey respondents (Hewitt, 1983) predicted that 25 percent of recording systems in use by 1990 will have at least 1000 channel capability and that this percentage could increase to 50 by 1995.
Offshore Exploration Potential
Authors: St. John B. 
Published: October 2008

ABSTRACT
There are 799 indentified sedimentary provinces which possibly could contain hydrocarbons. Of these, 481 are located offshore or partly offshore. Eight of the 481 are considered to have excellent future hydrocarbon potential, 34 good-to-excellent, 42 good, 72 fair-to-good, 100 fair, 80 poor-to-fair, and 145 poor.
There are numerous basins or provinces classification schemes attempting to equate type with hydrocarbon potential. The Bally and Snelson system and Klemme classification in current use indicate the most hydrocarbon-prone provinces are those formed on continental crust and associated with plate collision.
The identification, location, classification and seriatim of offshore future hydrocarbon potential can be utilized by explorationists to screen those provinces having relatively poor hydrocarbon potential and those politically and environmentally unacceptable. The elimination of the objectionable provinces will enable the explorationists to concentrate on the high potential areas with acceptable parameters.

INTRODUCTION
There are 799 sedimentary provinces identified on the map, Sedimentary Provinces of the World (St. John, 1984). The term "provinces" includes basins, foldbelts, carbonate banks, cratonic arches, and deep sea fan and cone deposits of 1,000 meters or greater thickness. Of the provinces, 307 are located offshore, 174 are sited partly on and partly offshore, and 318 are onshore. Only those 481 provinces located offshore or partly offshore are considered in this report. Table 1.

CLASSIFICATION
There have been numerous attempts to classify sedimentary basins, or provinces, and to relate the various types to hydrocarbon potential. Two of the most frequently quoted systems are Bally and Snelson (1980), and Klemme (1971). Not all of 481 offshore provinces have been classified by Bally and Snelson or Klemme, whereas some have been assigned two classifications where there is superposition of types. Table 2.
Numerically, the majority of sedimentary province considered offshore fall in Bally and Snelsons' genera types 1 and 3 and in Klemme's type III. However, a study of the location of known giant oil and gas fields (Carmolt and St. John, 1984), indicates the giants are found most commonly in provinces formed on continental crust and associated with plate collision. These are Bally and Snelson type 22, and Klemme type IIc.

SERIATIM
The 481 offshore sedimentary provinces are rated subjectively as to hydrocarbon potential. Political and environmental aspects are not considered. Table 4
The quality of hydrocarbon potential does not appear to be concentrated geographically but is distributed evenly worldwide. Table 5.
The offshore sedimentary provinces having ranking from Excellent through Poor -to-Fair are presented in a seriatim of declining hydrocarbon potential for the top 337 provinces (Appendix). The 145 offshore provinces considered to have Poor potential were not ranked.
Leg Strengthening of a North Sea Jacket
Authors: Forster M.L. 
Published: October 2008

ABSTRACT
Proposed changes to topside weight on a 9 year old North Sea jacket were going to create unacceptably high static stress levels on two legs within the splash zone.
These members were strengthened in advance by jacking 2200 kips out of each leg into steel sleeves, which were subsequently grouted and stressed around the legs.
The paper reviews the describes the evolution of model testing, fabrication trials and installation.
Areas of potential use and benefits to other offshore installations are discussed.

INTRODUCTION
As production platforms and their oil reservoirs age, topside loading requirements can change significantly. Additional well work over, new oil and gas processing requirements, together with associated additional accommodation needs, are all factors Which can lead to large topside load increases and/or redistribution. This is particularly relevant to the first generation of North Sea platforms which were installed prior to the existence of local case histories of aerial reservoir and operational needs. In addition, weight audits have shown in many cases, that the operational topside load was greater than the original design value.
Hence, static stresses due to axial loads in the jacket legs can assume great importance. The locations of the highest stress values can often occur in the splash zone, where corrosion is most virulent.
Just such a situation existed on the Occidental Group's Piper platform in late 1983. Further development of the 8 year old reservoir required the installation of new work over facilities. The stresses in two corner legs were such that this would not be possible without relieving some of the existing axial load in each leg.

SITUATION
The Piper field is situated 100 miles north east of Aberdeen in Block 15/17 in the U.K. sector of the North Sea. The field was discovered in January 1973, the jacket launched in June 1975 and production commenced in December 1976.
The all-steel platform sits in 474 ft of water and has the elevation shown in Figure 1. The derrick can be seen on the southern flank.
Following a series of design developments and loading increments, the topside load on the platform was scheduled to increase in 1984 by 10%, much of this to be applied near the south end.
The jacket framing from the underside of the Deck Support Frame at the +68 ft level, to below the -50 ft framing is shown typically for the south-west corner in Figures 1 and 2. The critical zone for loading is between the +20 ft and -50 ft framing where the corner legs are 48" diameter with 1.125" wall thickness. From -6 ft level to the +20 ft node a further ½" corrosion allowance of steel wall thickness is available. This splash zone has since been redefined such that corrosion should be allowed for to a depth of 10 ft below Lowest Astronomical Tide (L.A.T.) (1). To date, no reduction in wall thickness has been found, but the remaining design life of the platform is in excess of 15 years.
An Investigation of Dynamic Wind Loads on Offshore Platforms
Authors: Vickery B.J. , Pike P.J. 
Published: October 2008

ABSTRACT
A wind tunnel investigation of dynamic wind loads on a 1:400 scale model of the Exxon Company, U.S.A. Lena guyed tower offshore platform was conducted. The objectives of this investigation were to (1) investigate the dependence of wind loads on flow structure and turbulence intensity, and (2) obtain data necessary to permit an assessment of theoretical and semi-empirical methods of estimating the effects of dynamic wind loads on offshore platforms. There are two fundamental reasons for conducting this investigation. First, relevant experimental data on dynamic wind effects on offshore platforms is limited, and there is a need to improve the experimental data base upon which dynamic wind design procedures can be evaluated. Second, dynamic wind loads can contribute significantly to the design requirements of compliant offshore structures (e.g., the Lena guyed tower) because of the relatively long-period response of these structures.
This paper presents the major results of the experimental investigation and shows the results of a measured vs. calculated comparison of dynamic wind loads. The comparison shows that dynamic wind loads calculated using free-stream wind engineering theories are conservative relative to the model test data.

INTRODUCTION
Compliant offshore structures such as guyed-tower or tension-leg platforms are susceptible to wind loads which, under design conditions, may be responsible for over 25% of the overall response to wind, wave and current. Constant loads due to steady winds and currents are not counteracted by inertia loads induced by platform movement (compliancy) and thus, unlike wave loads, must be fully resisted by the platform restraints. In addition, the relatively long natural period or low natural frequency places such structures in the energy containing region of the wind turbulence spectrum and, despite the comparatively high hydrodynamic damping, the dynamic response to wind can be significant.
The development of compliant offshore structures has necessitated the development of wind design procedures that explicitly account for the dynamic interaction of the structure and the Wind. Unfortunately, the relevant experimental data base upon which the accuracy of such procedures can be evaluated is limited. A previous investigation of wind loads on offshore platforms by the authors [1] was concerned with mean loads under predominately steady, fully-coherent wind conditions. In the case of dynamic wind loads, however, the structure of wind turbulence, particularly the spatial characteristics of wind gusts relative to the spatial dimensions of the platform, should be considered.
The study presented herein is concerned with a detailed examination of both the mean and dynamic wind loads acting on a 1:400 scale model of the Exxon Company, U.S.A. Lena guyed tower offshore platform when placed in correctly scaled turbulent shear flow.