bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Requirements for the Effective Transfer of Environmental Loadings in a Subsea Wellhead System
Authors: Milberger L.J. , Yu A. , Hosie S. , Hines F. 
Published: October 2008

ABSTRACT
This paper reviews the evolution of design requirements for subsea wellhead housings used in offshore drilling. Structural integrity is paramount in order to resist environmental loadings. A new wellhead design incorporating a pair of axially spaced tapered sockets is presented. Results of detailed computerized analysis along with test data on a full-scale test article are presented. A review of field operations for the new design is presented along with the design of a tool which can be used to seat the sockets, thus making the system useful for extreme fatigue-rated drilling.

INTRODUCTION
Early subsea wellhead system designs used a single landing or support shoulder between the 18-3/4" subsea wellhead (HP housing) and the 30" conductor housing (LP housing). This type of configuration was found to operate well and provided years of successful operation until two field failures occurred[8][1]. Both involved drilling in high current conditions. Hopper[1] reports that an exploration well being drilled in the North Sea west of Shetland had to be abandoned 29 days after running the HP housing due to the fatigue failure of the weld between the casing extension and the wellhead body.
These unexpected failures of subsea wellhead housings during drilling operations prompted an in-depth study into the behavior of a subsea wellhead system when it is subjected to external bending loads. Most of these studies were completed using simple two-dimensional finite element analysis and a maximum bending moment of about 1 million foot pounds, as discussed in references [3], [4], [5], [6], and [7], although reference [2] clearly addresses bending loads above 2 million ft.-lb. The results of all these studies showed that the magnitude of the bending stresses developed in the casing extension below the high pressure wellhead housing is greatly affected by several factors:Type of interface between high and low pressure housings, i.e., single or double socket type.The radial clearances which exist at the socket.The effective cement level in the annulus between the 30" conductor and the 20" casing extension.The size of the wellhead extension.The amount of applied load.
Further, these studies showed that to ensure a subsea wellhead system has sufficient structural integrity to endure the static and fatigue bending loads which may be encountered during drilling and production operations, a wellhead system should preferably employ a dual socket interface with the radial clearance at these sockets suitably adjusted to the vertical distance between the sockets.
The magnitude of environmental loadings continued to increase with the introduction of Tension Leg Platforms (TLP), because drilling or production risers on these vessels remain connected to the subsea wellhead system in all conditions. This factor automatically results in a considerable increase in the static and fatigue loading which the wellhead system will experience.
A 78° Extended Reach Well in the Gulf of Mexico, Eugene Island 326 No. A-6
Authors: Kimball C.F. , Colwell C.N. , Knell J.W. 
Published: October 2008

ABSTRACT
This paper describes the successful drilling & completion of Forest oil Corporation's OCS-G-5518 No. A-6, Eugene Island Block 326. The subject well was drilled as a 79 deg high angle extended reach well (ERW) from an existing production platform in the adjacent Eugene Island Block 325. The purpose was to establish production from a shallow sand located at a depth of 2300 'TVD(701M) at a reservoir take point located 7000' (2134M) from the existing platform. The paper focuses on the engineering aspect of the well plan and the operational problems that were encountered.
The final results indicate that a shallow extended reach well with an MD/TVD ratio of 3.1:1 can be successfully drilled and completed in the Gulf of Mexico. The techniques used and the lessons learned can be applied to any area with modifications for that particular drilling area. Existing platforms can be used to cut cost and to protect adjacent leases as "Held By Production". New platform placement can take into consideration the drilling of extended reach wells.

INTRODUCTION
Forest oil Corporation (FOC) drilled a discovery well, OCS-G-5517 No.3, in Eugene Island Blk 325 in November of 1987. The well was a straight hole drilled to 6100'MD/TVD(1859 M). A six well drilling template was then placed over the No. 3 well and several additional wells were drilled using a jackup drilling rig in 255'(78 M) of water.
Another discovery well, OCS-G5518 No.2, was drilled in Eugene Island Blk 326 in March of 1988 to 4939'MD/TVD(1505 M). This well found a productive sand at 2300'(701M). A platform was then set over the drilling template in E.I. Blk 325 and tieback and completion operations were begun. Figure 1 shows the location of Eugene Island Blocks 325 and 326.
It became necessary to establish production from E.L Blk 326 and "HOLD IT BY PRODUCTION" in an economical manner. Several options were considered.Set a minimum offshore structure (MOSS) over the existing discovery well in Block 326, install test facilities only, and flow to the existing platform in Block 325 for processing.Perform a subsea completion flowing to the existing platform in Block 325 for processing.Drill and complete an ERW from the existing platform in Block 325.
The cost analysis showed that options 2. and 3. would cost approximately the same and that option 1. would cost twice as much as the other two. Because of the cost and because of the mechanical problems often associated with option 2., option 3. was chosen. The basic directional plan was as follows.Build at a rate of 6 deg/100' from the surface to a maximum angle of 77 deg 19 min at 1389'MD(423M)/1000'TVD(305M).Hold the angle of 77 deg 19' to a total depth of 7169'MD (2185M)/2300'TVD (701M).
This plan resulted in an MD/TVD ratio of 3:1:1. Figure 2 shows the spider plot of the wells drilled from the Eugene Island Block 325 production platform.
Pigging of Subsea Pipelines
Authors: Schaefer E.F. 
Published: October 2008

AN ART?....A SCIENCE??
As offshore developments move into greater water depths the problems of slugging, associated with condensate drop out and two-phase flow in gas pipelines becomes particularly acute at the pipeline riser. These vertical sections of pipe, some of which are over 350 m high, present some interesting problems in relation to slug formation and removal as the pressure varies due to the head of liquid which may build-up during some operational phases.

Factors Affecting Two-Phase Flow

Gas-Liquid Ratio
The basic behavior depends on whether or not both the liquid and gas phases are present as a continuous phase.
In bubble flow, one has a series of bubbles of gas in the liquid, and gas N not in a continuous phase.
At the other end of the scale--spray or mist flow, small amounts of liquid are suspended in the gas. Now, liquid is now the discontinuous phase and the gas is the continuous phase.
In systems where both the gas and liquid are continuous, the character of the flow is more difficult and de ends on such variables as phase densities, viscosities, and velocities of each phase.

Volume/Flow
Under certain conditions, constant flow can be maintained without the use of spheres, if the flow velocity is sufficient to keep the liquid moving. However, under most conditions, periodic pigging must be maintained to provide the maximum efficiency.

Operating Pressure/Design Pressure
As liquid columns increase in size in each valley, the total pipeline pressure differential increases to the point where up-stream pressure may be increased in excess of the MAOP (maximum allowable operating pressure). The importance of periodic pigging is now obvious.

Allowable Pressure Drop
Liquids that sag in valleys cause pressure differentials as the gas pushes the liquid level to the point where the gas has to bubble through the liquid column in order to maintain flow.

Velocity of the Gas-Liquid
Due to the interaction between discrete phases, the gas moves more rapidly than liquid and can cause problems down-stream as the column of fast-moving liquid comes to the slug catcher.
During the life of a pipeline, depending on the transported fluid and its service conditions, the pipe wall will deteriorate, possibly through corrosion or as a result of scale or other solid deposits adhering to it.
This will cause the deterioration in the economics of the pipeline operation due to increased pressure drop in one of two ways, Firstly, the deposits may effectively reduce the pipeline diameter and thus its throughput capacity and secondly, the roughness of the pipe wall may be increased with its attendant adverse effect on pressure drop.
For example, the presence of wax in crude oil can lead to the precipitation of wax deposits on the pipeline wall. This wax deposition is time dependant but a thin layer can build up quickly to produce, on larger throughputs, significant reductions in line capacity.

Why Pig?
There are basically four reasons for pigging a pipeline.
A Preliminary Case for the Existence of Hurricane Alleys in the Gulf of Mexico
Authors: Cooper C.K. 
Published: October 2008

ABSTRACT
A review of hurricane intensity in the Gulf of Mexico suggests there are two alleys where hurricanes are roughly 20% more intense than elsewhere. This paper develops a physical basis for the alleys using previous modeling and observations, and a statistical correlation of historical hurricane intensity and ocean temperatures. While the evidence for alleys is persuasive, final acceptance will depend on results of further research.

INTRODUCTION
Historically, designers and engineers have generally assumed that hurricane paths are random. This is based largely on the work of Haring and Heidemanl and Ward et al.2 who analyzed the ODGP wind and wave hindcast of 26 historical hurricanes in the Gulf of Mexico. While they found signMcant variations between sites, analysis showed that the differences were not statistically significant. In other words, the hindcast data suggested one region of the Gulf was as likely to experience a severe hurricane as another.
The recently completed GUMSHOE (GUlf of Mexico Storm Hindcast of Oceanographic Extremes) study enhanced ODGP by including more storms and shallow-water wave physics. As in ODGP, substantial spatial differences appear in GUMSHOE with three regions standing out a mild region off central and eastern Texas, and two severe regions off Mississippi and western Texas (denoted by L for low, He for eastern high, and Hw for western high, respectively). The regions are clearly evident in Figure 1 which shows contours of the central pressure deficit (peripheral minus central pressures), a good measure of hurricane intensity. Two dark arrows superimposed cmthe map denote "alleys".
77hepressure differences between the severe and the mild regions correspond to a 3-4 m difference in maximum wave height using the parametric model of Coopcr3. Existing RP2A criteria suggest a spatially uniform wave height. If designers had confidence that the differences in regional severity were due to a real physical phenomena and were not statistical aberrations, they could improve the reliability of their designs. Haring and Heidemanl and Ward et al.2 do not provide the necessary confidence - they suggest the regional differences are statistically insignificant. However a recent analysis of the GUMSHOE statistics by Chouina.rd4 suggests there is a statistically signitlcant variation over length scales of 100 km.
A close look at the physics of hurricanes and the climatology of the Gulf waters seems to provide a physical explanation for the alleys in Figure 1. The explanation: the two alleys reflect the influence of subsurface warm water on hurricane intensity. Figure 2 gives some support for this hypothesis. It shows the mean water temperature at 60 m depth in the Gulf of Mexico during hurricane season. A comparison of Figures 1 and 2 shows the two alleys correspond closely to the two warm water regions. The two regions in Figure 2 originate from the Loop Current and its eddies which bring warm Caribbean water into the Gulf as summarized by Elliot5.
Spatially Weighted Trim Stacking: A Technique for Prestack Noise Suppression
Authors: Holcombe H.T. , Wojslaw R.S. 
Published: October 2008

ABSTRACT
Spatially Weighted Trim Stacking (SWTS) is a nonlinear seismic noise suppression process that works well on raw pre-stack data. It is a robust, efficient, and algorithmically simple operation that is best performed on CMP gathers prior to any other pre-stack data processing. Generally it improves signal-to-noise and increases trace-to-trace coherence, thereby enhancing the effectiveness of downstream pre-stack processes, such as DMO and multiple suppression. Also, it virtually eliminates transient noise and interfering crew noise in marine data.

INTRODUCTION
The fundamental premise of the Spatially Weighted Trim Stacking (SWTS) process is to make use of prior knowledge of some inherent characteristics of seismic data to identify and reject noise. The key assumptions are (1) that seismic data are coherent along some predominant local dip, and (2) that the amplitude varies slowly along that dip.
The process is a simple, sample-by-sample operation performed in the x-t domain as a roll-along process. First the predominant local dip is determined, over a specified number of traces, immediately adjacent to the trace containing the sample in question. To remove outliers, an alpha-trim is then performed on the samples along the predominant dip. The data sample is then replaced with a normalized, spatially weighted stack of the remaining sample values.
The "alpha-trimmed mean" or "trimmed mean stack", originally proposed by Watt and Bednar, 1983, has been shown to be effective in suppressing some types of transient and coherent noise (see Haldorsen and Farmer, 1989). Further, automatic dip determination and weighted stacking are common in many seismic data processing algorithms. However, to our knowledge, the simultaneous combination of dip determination, alphatrim, and weighted stacking (as implemented in the SWTS process) has not previously been tried. In our testing efforts SWTS has usually been more effective, in dealing with a broad range of noise problems, than the various spectral techniques in common use (see Luh, 1991, and Galbraith, 1991). Computationally, it is far more cost efficient than the F-K, F-X, and tau-P techniques when operating on pre-stack data.

P DETERMINATION
The automatic dip determination implemented in SWTS is somewhat unique and operates in the following way. A roll-along buffer is set up that contains an odd number of traces (typically 9 or 11) symmetric about the trace containing the data sample in question. A dip search is conducted over a specified dip range, in both lateral directions independently, from the sample in question to the edge of the roll-along buffer. A maximum semblance criterion is used for selecting each dip. The two maximum semblance values are compared and if they are close, all the sample amplitudes along dip are saved for the subsequent trim and weighted stack. If they differ by a significant amount, only samples for the dip of higher semblance are saved. This facilitates proper handling of edges and event terminations.
Recent Model Tests With Suction Piles in Clay and Sand
Authors: Steensen-Bach J.D. 
Published: October 2008

ABSTRACT
The beneficial effects of suction on the break-out resistance of short, hollow piles (I.e. suction piles) in clays as well as sands have been verified by model tests. For sands increased break-out resistance is proportional to the developing suction inside the pile. For clays the increase in break-out resistance is due to a suction induced transition from local failure along the shaft to a reversed bearing capacity failure.

INTRODUCTION
As a part of a research programme on the utilization of suction piles as foundation for small light-weight platforms of mono tower type model tests were carried out in connection with the development of a design procedure. This paper presents model test results and their preliminary interpretation.
Steel tubes closed at the top and installed in the seafloor by the differential water pressure obtained when pumping from the pile interior is termed suction piles.
The literature on suction piles deals primarily with the conditions for installing and anchoring by the differential water pressure created from continued pumping. The possibility of utilizing the differential pressure created by the piles themselves, when subjected to uplift is investigated in this paper.

TEST PROGRAMME
The total test programme analyzed includes tests on Kaolin l, Nivaa Clay and G12 sand2 . Variable test parameters comprise:Pile diameterEmbedment/diameter ratioSoil typeUndrained shear strength of claysLoad type (monotonic, sustained)Regeneration time prior to loadingRate of monotonic breakoutMagnitude of sustained breakout load

THEORETICAL CONSIDERATIONS

Breakout from clays
The short term breakout capacity of embedded objects has been suggested determined by the use of plasticity theory on general shear failure mechanisms. Model tests at embedment ratios less than 1 support this3, 4. At larger embedment ratios 3 different failure mechanisms, (i)-(iii), have been recognized 1,2 . as illustrated in Fig. 1:General shear failure in terms of a reversed bearing capacity failure is formulated [1]: (available in full paper)
The value of N which is determined at the time of maximum breakout force F, and inserting a as the ultimate value in [II, is termed N1 The value of N that fulfils the vertical equilibrium equation [2] for the clay plug at the time of maximum breakout force, (inserting a as the ultimate value), is termed N2 (available in full paper)Local tension failure occurs when the inside soil-wall friction and suction exceed the tensile strength of the soil [3]. A clay plug inside the pile is then torn apart from the seafloor leaving a hole: (available in full paper)
(iii) If no suction is allowed to develop inside the pile, the soil-wall friction cannot exceed the tensile strength of the soil and failure develops as a local shear failure along the pile shaft [4]:(available in full paper)
Notations used in [1],[2],(3) and (4) are outlined in Fig.2.
Deltas as Petroleum Provinces: Past, Present, and Future
Authors: Wescott W.A. 
Published: October 2008

ABSTRACT
Deltas have proven to be important worldwide petroleum provinces for two main reasons. Firstly, they are point sources from which sediment is introduced onto continental shelves and into marginal basins, where the interaction of fluvial and basinal processes frequently result in favorable associations of reservoir, source, and seal facies. Secondly, the progradation of deltas forms a geomorphic bulge which projects seaward and allows land and shallow offshore drilling rigs to reach deep targets which could only be reached by more expensive rigs in deeper water areas adjacent to the delta. Significant hydrocarbons have been discovered at least eighteen deltaic provinces worldwide. Almost 30 billion BO and over 100 TCF of gas have been produced from these deltaic provinces, which contain estimated ultimate reserves of 50+ billion BO and 350 TCF of gas. Fields with reserves greater than 500 MMBO occur in five deltaic basins and fields with more than 100 MMBO have been found in thirteen deltas. Future exploration efforts will focus upon deepwater delta-front environments and smaller deltas in more remote areas with hostile drilling environments, such as those in the circum arctic region.

INTRODUCTION
Ever since Herodotus described the land at the mouth of the Nile River as similar in shape to the Greek letter delta around 400 B.C. deltas have become one of the most studied of all depositional environments.1'2 Deltas form where fluvial systems enter a body of water and have been geologically defined as: "The low, nearly flat, alluvial tract of land at or near the mouth of a river, commonly forming a triangular or fan-shaped plain of considerable area, crossed by many distributaries of the main river, perhaps extending beyond the general trend of the coast, and resulting from the accumulation of sediment supplied by the river in such quantities that is not removed by tide, waves, and currents. Most deltas are partly subaerial and partly below water."z Deltas are significant components of many coastlines and their deposits make up a substantial volume of the stratigraphic record.1,3,4,5,6,7 Mfosdte7rn deltas are diverse in form and vary greatly in size and geomorphic setting. Deltaic morphology and three dimensional distribution of sediments is the result of a complex interplay between fluvial discharge, sediment supp" and the wave and tidal energy of the receiving basin. They occur at almost a" latitudes and climates, from the arctic the tropics.3
Impact of Offshore Drilling in the Eastern Gulf of Mexico
Authors: Shinn E.A. , Lidz B.H. 
Published: October 2008

ABSTRACT
Six exploratory oil well drill sites were examined with a two-person submersible in water depths ranging from 21 to 149 m (70 to 490 ft). Time since wells were drilled ranged from 15 months to 17 years. The area of visually detectable cuttings around recently drilled wells in depths greater than 45 m (148 ft) ranged from -2,539 m2 (27,320 ft2) to -13,352 m 2 (143,668 ft2). At the shallowest site, the area with cuttings was only -20 m2 (215 ft2).. All visually observed impacts were mainly mechanical, such as debris, and anchor or jackup-leg scars. No lasting impact was observed at the 17-year-old site.

INTRODUCTION
Public concern over offshore drilling, especially off California and south Florida, has risen steadily since the early 1970s. Although two National Academy of Sciences reports 1,2showed offshore drilling to be safer than tankerage, events such as the IXTOC- 1 blowout, the Exxon Valdez tanker spill, and more recently, the Persian Gulf wars have served to punctuate public concern. Political pressure, and public concern, exacerbated by a lack of credible environmental data and highlighted by a recent National Academy of Sciences panel review Report3 and a State of Florida Governor's Report,4 led to a drilling moratorium on the southwest Florida shelf.
The purpose of this paper is to present observations, made on the basis of direct underwater examination, of six exploratory well sites in the eastern Gulf of Mexico. The wells were drilled between 1972 and 1990. This study builds on an earlier study of five well sites off the Florida Keys, where wells were drilled between 1959 and 1961. That study also included two deep-water sites drilled in 1981 nd 1986. Both studies were funded by the Minerals Management Service (MMS) EnvironmentalStudies Program. The first study, conducted in 1988, has been published in the biological literature,5 as an MMS technical report,6 and was visually presented in a 21- minute video.7 Field work for the second study was conducted in November 1991, and a thorough analysis of the data and bottom samples that were collected is in progress.
Well sites in the 1991 study ranged in depth from 21 m (70 ft) to 149 m (489 ft), and the youngest site had been spudded only 15 months before our examination (Fig. 1, Table 1). The oldest site was drilled 17 years before our examination. Another site, Gainesville Block 707, had been the subject of an extensive pre-drilling assessment and monitoring study during drilling. 8 The results of those studies were rendered questionable when Hurricanes Danny (Aug. 16-16, 1985) and Elena (Aug. 31-Sept. 3, 1985) swept the bottom while the study was underway. Evidence of drilling impacts were for the most part destroyed, and the study was terminated. 9,10