bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Design of Offshore Supply Vessels
Authors: Mok Yingkei , Hill Ralph C.
Published: October 2008

The offshore supply vessel came into being in 1954 to meet the demands of a rapidly growing offshore oil industry. The authors give a brief history of this development and present the arrangement and profile of atypical supply vessel as well as a complete table of characteristics on a number of vessels.

It is shown how the demand to carry large quantities of cargo on deck resulted in a somewhat unique hull form. Two particular areas of design are stressed, stability and powering. The question of stability is gone into in detail, including development of the current USCG stability criteria. The difficulty in estimating power requirements for the low speed length ratios associated with supply vessels is brought out. Data for estimating power requirements is presented.

The views expressed in this paper are those of the authors and do not necessarily represent the official view of the American Marine Corp. or the USCG.

INTRODUCTION

When the first offshore oil well was drilled in the Gulf of Mexico at the end of World War II, the need for delivery of supplies such as drill pipe casings; drilling mud; cement, etc., brought forward a new type vessel--- offshore supply vessel.

Among the first offshore supply vessels were the war surplus LCT's, primarily because they were readily available. They were adequate for the early offshore drilling sites close to shore. When new vessels were built, they were designed closely to the LCT's with the pilot house aft. Then in 1954, a new type of supply vessel came into being which was to set the pattern for the offshore supply vessels that were to come. These vessels had all of the crew quarters forward leaving a large deck area aft for carriage of deck cargo. Connection between the forward quarters and the engine room aft was through a passage under deck.

During the last 15 years, because of the rapid worldwide development of offshore oil fields, we have seen not only bigger, faster and more seaworthy supply vessels built, but have also witnessed the use of these vessels in many different roles. Offshore supply vessels have been used as seismographic exploration vessels, oceanographic research ships, tenders for deep diving submarines, telephone cable laying vessels, container ships, anchor handle vessels and seagoing tugs. This paper, however, will limit discussions only to the vessels that carry supplies.

It is the intention of this paper to provide designers and operators with a better understanding of the stability characteristics of offshore supply vessels, and to contribute some information concerning preliminary design structural design, and powering requirements, all of which have been lacking in this fast growing field.

ON THE PROPORTIONS AND ARRANGEMENT

The characteristics of 20 offshore supply vessels are given in Table 1. For quick reference, the average values of some of the particulars are plotted on Fig. 1.
Potential ties of Explo tlng Marine Algae
Authors: Claus George
Published: October 2008

Marine algae have been utilized by man since prehistoric times as food, drugs or raw materials for chemicals; however, their more concentrated exploitation dates back only to the past 50 years or so. The discovery, isolation and purification of polysaccharides in the brown and red algae with characteristics favorable for different industrial applications created such a demand for these plants that worldwide shortage resulted, causing a keen competition among nations for the control of natural growing beds. Calculations are presented on the total potential world supply of harvestable algae and alternative solutions for satisfying the growing demands of the phycocolloid industries are discussed, including the current efforts to grow algae under controlled conditions for predictable harvests. The feasibility of such aquaculture ventures is evaluated and the pros and cons of creating algae factories are pointed out.

TEXT

Marine algae are lower plants restricted to the salt water environment. They range in size from the microscopic unicellular organisms to the largest plants on the earth. Certain groups of them reach considerable dimensions and are called kelps in general.

According to their pigmentation, one Distinguishes among green, brown and red algae. All three groups are quite distinct and were already recognized by the Romans. Different uses date back to early historic times, both as food and medicaments. The brown algae were found to accumulate large quantities of iodine in their bodies, and dried weeds were already used in ancient China for the treatment of goiter. Some green algae are still cooked especially by Oriental people - into soups or made into salads) while red algae are smoked and sold as a delicacy in many of the Nordic countries. These uses of algae, however, did not warrant their large-scale exploitation. Only the discovery in this century that both the brown and red algae contain substances which are relatively easy to extract and have characteristics useful in different applications, lead to the foundation of what might be termed seaweed industry.

Most of the marine algae have a highly slippery consistency, which is due to mucous substances which they manufacture in their cells and secrete toward the environment. These substances serve the protection of the plants and all have one common characteristic -- they are made up of long polymers of different sugars.

Since they will produce a colloidal system in water, they fall into the category of hydrocolloids and since. They are obtained from algae) the Greek name of which is Phykos, they are termed phycocolloids. In modern industry there are basically three such colloids which are Widely utilized: [1] algin, or alginic acid) and its different salts obtained exclusively from brown algae; [2] agar-agar, produced by certain red algae and [3] carrageen in, extracted from other red algae.

Alginates are widely utilized in different foods for the high viscosity solutions they produce where such requirement is present, as in creams, to which they impart a better whipping ability.
The Use Of Coated Fabrics In Containment Of Petroleum
Authors: Headrick Richard T. , Headrick Edward E.
Published: October 2008

Some 30 years of experience in coated fabric fuel containment indicates similar permanency and sharply reduced fire hazard when compared with conventional metal containers. The use of "embankment liner tanks" with integral fabric floating roofs is common for water reservoirs and is now being examined for petroleum containment in refinery tank farm areas. Inflation of roofs with nitrogen atmosphere and available foam systems further reduces contamination and fire hazard. In the area of oil spills, coated fabric tents have been installed on the ocean bottom off Santa Barbara effectively collecting oil and gas seepage from the bottom and conducting the product to an adjacent platform or floating collector tank. Tent sizes range from 25 feet square to 115 feet square. Floating tanks may have any capacity, but one used successfully in the Santa Barbara channel is 10.000 gallons and is 22 feet square when empty. Another tent use is collecting fresh water from underwater springs in the ocean. This is planned for Ventura County, California. A collapsible oil containment boom has been developed for open ocean use which weighs under 2 1bs. per foot. Under development is a skimmer system to receive oil from the boom legs. Projected performance is to clean a 250 foot wide strip of sea at 3knots per hour in relatively heavy sea. The unusual boom design does not attenuate or deflect wave energy, has very little draft and freeboard and precisely contours wave surface contour & Materials used in ocean environment generally are based on nylon cloth coated with PVC or synthetic rubber, such as neoprene, Nitrile, Buna-N or Hypalon, compounded for resistance to petroleum, sea water and ozone and not sustaining combustion. This paper will emphasize the use of coated fabrics in oil spill control, substantiated by years of experience in using coated fabrics in difficult fuel containment problems, largely for the military.

INTRODUCTION

In 1939, the U. S. Army Air Corps approached Firestone with view toward developing rubber membranes to line calf hide tanks for aircraft fuel to reduce leakage. Firestone suggested substituting tire cord fabric instead of calf hide. Later, nylon cloth was substituted for tire cord to further reduce weight. Thus, modern aircraft tanks were born. Within two years, Firestone technology had tackled the complex problem of self-sealing tanks which were used with great success in World War II. The use of synthetic rubber coated fabrics for ground storage fuel containment has reached maturity after 25 years of very useful service largely for the military. The first ground systems were constructed for the Marine Corps as a "fuel system supply point" which was subsequently copied by the Army. Some of the original tanks are still in use. Literally thousands of tanks have been employed in the arctic for Dew Line since 1957 and more recently to support North Slope petroleum activities. Substantial capacity systems provide instant conversion of an "airbase of opportunity" into a sophisticated fueling depot.
Acoustic Valve Operating System
Authors: Haase W.H.
Published: October 2008

As offshore pipeline systems expand into areas great distances from shore, and into deep waters, a method for locating and controlling isolated underwater valves is required.

The Bendix approach to fulfilling this requirement is the Acoustic Valve Operating System (AVOS). The system features coded interrogation, coded command, and five-year life. The coding, accomplished by using multiple frequencies, is designed to prevent unauthorized or accidental valve actuation.

A selected valve can be located from a three mile distance, and can be commanded to open or close from one-half mile. Range to the valve and actual status are automatically displayed and updated by a frequency coded reply to each interrogation.

In addition to performance requirements, the data presented includes design considerations, hardware items, and test data resulting from a Gulf installation.

INTRODUCTION

A need has developed for an easier way to operate isolated valves on offshore pipelines. While this requirement is primarily based on safety considerations and production convenience, it also bears upon pollution control.

The present method involves a diver's manual control of a valve. Although this method has been used for many years, it is slow and at times impossible due to weather and the diver's inability to locate the device. In fact, the time when you most want to operate a valve is usually during the worst possible weather, when diving may be impossible.

With these thoughts in mind, Bendix (working in conjunction with Tennessee Gas Pipeline Company) has developed an acoustic valve operating system (AVOS).

Several persons in the industry have stated that they have had valves down for years and never needed to operate them. This state of affairs, however, is true only of pipeline systems of the past, which offer little flexibility in today's market (these old systems use platforms with expensive risers as control points). In the future, we may see fewer structures used as control points. Pipeline systems will provide greater operating flexibility; flow will be stopped, reversed or split, and side systems cut in and out more quickly.

Most pipelines of today are located within reasonable diving depths and at medium distances offshore. As distance and depth increases, the need for a remote valve operating system becomes more apparent.

Design and Performance Requirements

The Acoustic Valve Operating System functions are as follows (see Figure 1):Provide a means for locating an isolated valve from at least three miles (equivalent sea state 3) acoustically.Report status of valve from three miles. The valve is either open or shut.Provide a means of commanding a desired valve to change status from the surface within approximately 1/2 mile range.The equipment in water at the valve is designed for a five-year, unattended life (including the battery pack).The surface equipment must be portable and usable from a typical crew boat, with no special installation requirements.
A Surface Tree Riser Tensioning System for FPSOs
Authors: Pollack J. , Poldervaart L. , Naciri M.
Published: October 2008

Today hard riser, dry tree systems not carried on a bottom founded structure are supported by either a TLP or Spar. Both of these systems directly or indirectly use buoyancy to achieve the riser tensioning. The use of buoyancy requires that the relative motions of the buoyancy and the risers be kept small. The TLP does this by tendon restraining the buoyancy, while the Spar does this by creating a somewhat quiescent water shaft in which buoys can effect a relatively uniform riser tension. The physics of an FPSO require that the tensioning system cope with draft changes and larger relative motions between riser and floater. A weight-based riser tensioning system has been developed and tested which is able to cope with both the large stroke and relative motions required to make hard risers practical for FPSO systems.

Introduction

Deep-water hydrocarbon production in depths above 500 m uses two generic modes of development. This involves either an FPSO with wet subsea trees and flexible risers, or motion restrained floaters like TLP or Spar with dry trees and hard risers. Dry tree systems are the preferred means for producing these reservoirs as it gives better well control, intervention and workover leading to optimum reservoir depletion. Unfortunately developments of fields in remote areas often require storage and thus FPSOs with wet trees make better economic sense. To overcome this dilemma, a riser tensioning system has been developed which enables dry tree production from a spread moored FPSO.

To realize a proper FPSO tensioning system, the system must be designed to cope with draft changes and with larger and faster motions between the FPSO and riser. To deal with this a tensioning system based on weight rather than buoyancy was developed. The weight lateral motion is controlled by placing it in the water, well below the FPSO from which they are suspended by tension members running over sheaves. This riser tensioning system named Tension Leg Deck (TLD) will be detailed. The basic physics of this tensioning system will be described along with corroborating model test results. The present day existence of hardware required to construct this tensioning system will also be discussed.

Deep Water Hard Riser Production

Systems that can support hard risers for dry production trees and surface BOP offer many benefits over those using wet trees and subsea BOP. The main benefits are those of surface control, access and the ability to perform low cost interventions and workover over the life of the field. The floating platforms required to support these hard risers in deep water are however more costly than floating platforms for wet subsea production and drilling. Examples of these lower cost platforms are weathervaning FPSOs which are being used to receive, process, store and offload crude from subsea or fixed surface facilities. More recently spread moored FPSOs are being used and considered for milder deep water areas like West Africa and Brazil.
Terra Nova - The Flow Assurance Challenge
Authors: Stephens P. , Sheorey U. , Isenor R. , Ewida A.
Published: October 2008

The Terra Nova field is the second largest oil field discovered to date in the Jeanne d'Arc basin on the Grand Banks, with recoverable reserves of approximately 370 million barrels. The field, located in approximately 94 m of water 350 km East-Southeast of St John's, Newfoundland and 35 km Southeast of the Hibernia field, will be developed utilizing subsea flowlines from four drill centres tied back to an FPSO.

This paper discusses the design approaches adopted to meet the principal flow assurance challenges for the subsea facilities. These are:Hydrate formation: the minimum seabed ambient temperature is -2 °C.Wax formation: the design is based on stabilised crude having a wax content of 9.0 %, a pour point of 12 °C and a wax appearance temperature of 46 °C. The wax dissolution temperature is 70 °C.The implications of turret disconnection: the buoy along with all the risers can be released to allow the FPSO to move off-station to avoid icebergs.

The owners of the Terra Nova field are Petro-Canada (29 %), Mobil Oil Canada Properties (22 %), Husky Oil Operations Ltd. (17.5 %), Norsk Hydro Canada Oil and Gas (15 %), Murphy Oil Company Ltd. (12 %), Mosbacher Operating Ltd. (3.5 %) and Chevron Canada Resources (1 %). The operator of the field is Petro-Canada, and the FPSO vessel constructor is Daewoo of Okpo, South Korea.

The participants in the Terra Nova Project Alliance include Petro-Canada (and seconded owner personnel), Coflexip Stena Offshore Newfoundland Ltd., Shawmont Brown and Root, Halliburton Energy Services, FMC Offshore Canada Inc, PCL Industrial Constructors Inc. and Doris Conpro Ltd.

First oil from Terra Nova is targeted for January 2001.

Introduction

The Terra Nova development is based on a subsea tieback with flexible fowlines/risers to a Floating Production, Storage and Offloading (FPSO) vessel, with crude oil transported to market by shuttle tankers. The FPSO has a storage capacity of 970,000 barrels of oil and supports topsides process and utility equipment with a gross operating weight of 12,200 tonnes. The topsides facilities are designed for a maximum overall oil production rate of 23,880 Sm3/d (150,000 bbl/d), produced water rate of 21,000 Sm3/d (132,000 bbl/d), water injection rate of 28,600 Sm3/d (180,000 bbl/d) and gas injection rate of 7.36 MSm3/d (260 mmscfd). Following separation to meet the specifications for TVP of 75.8 kPa at 50 °C and BS&W of <0.5 % by volume, crude is transferred to the storage tanks located in the vessel hull where it is maintained above the wax appearance temperature at all times. The overall field schematic (base case development) is shown in Figure 1 and a simplified topsides process flow diagram is shown in Figure 2.

The base case subsea development scenario incorporates 14 production wells and 10 water/gas injection wells. Gas lift facilities are provided on 12 of the 14 production wells.
Operational Experience with the FPSO Ocean Producer
Authors: Thompson Richard
Published: October 2008

This paper describes and analyzes the operational experience of an FPSO (floating production, storage and offloading system) that has been onstream offshore West Africa for over eight years. The FPSO was designed for efficient production of smaller and marginal oil fields. It was converted on a stringent budget at an U.S. Gulf Coast shipyard and has been operated so as to be cost-effective at production rates ranging from 10,000 bopd to less than 5,000 bopd. Despite the economic constraints that have characterized its operation, it has achieved excellent results for safety and for overall vessel and process system uptime.

This paper discusses the design of the FPSO, it's operating history and operational results. The operating philosophy and procedures are examined in detail to illuminate their relationship to the successful results that have been achieved.

The operations philosophy, systems, procedures, and safety programs that are in place to help achieve the safety, uptime, and OPEX goals are presented. A case history of the FPSO is also presented.

Introduction

The FPSO Ocean Producer has been in operation in West Africa since December, 1991. During that more than eightyear period, the Oceaneering vessel crew has experienced no Lost Time Accidents (LTA). Since 1994, the Ocean Producer has processed over 10,000,000 barrels of oil while maintaining 99.9% uptime. The safety record and uptime achievements have been maintained while operating costs were constrained to allow continued operations at oil production rates of less than 5,000 bopd.

The FPSO Ocean Producer was originally designed and built to treat 15,000 bfpd of heavy oil with up to 80% water cut.1 She was put into service in 1991 for Amoco Gabon Gombe Marin Company and remained in Gabon until the end of October, 1993. At that time, she underwent minor modification and moved to Angola where she is currently under contract to Sonangol P & P processing light crude oil.

The FPSO Ocean Producer was converted from the 78,000-dwt crude oil tanker M. T. Baltimore Sea for FPSO service at the Gombe Beta field offshore Gabon, West Africa. The Gombe Beta field failed to produce up to expectations, and Amoco sold its interest to Kelt Energie in 1992. The FPSO remained on location on a month-to-month basis producing at very low rates. In September 1993, the Ocean Producer was contracted to Sonangol P & P for Kiabo field, Block 4, Angola. This was the first (and still the only) direct contract of a floater to an operating unit of a West African national oil company.

Following its release from Gombe Beta field, the Ocean Producer sailed to Capetown, South Africa, for minor modifications and refurbishment. She then proceeded to Kiabo field, arriving only 57 days after departure from Gabon.

Original proven reserves for the Kiabo field was on the order of 5,000,000 barrels, with some upside potential. To date, The Ocean Producer is still in operation in the Kiabo field and has recovered over 10,000,000 barrels.
On The Coupling Terms In The Low-Frequency Viscous Reaction Forces Of Moored Tankers In Deep Water
Authors: Wichers Johan , Ji Chunqun
Published: October 2008

Due to the restricted water depth of experimental facilities one has to rely more on computational tools for the design of turret and spread moored tanker based FPSOs in deep water. These tools have to be as accurate as possible.

The mechanics to compute dynamically mooring lines and risers are understood. By means of potential theory the first order tanker motions and wave drift forces with and without current can be adequately computed nowadays, see for instance Ref. 1.

Besides the low-frequency (lf) wave drift forces also the lf viscous reaction forces (damping) exist in still water and current. The lf reaction forces/moment induced by the lf motions in the horizontal plane are mostly dominated by viscosity and hardly to compute.

By means of model tests the viscous forces in the separate surge, sway and yaw modes of motion were measured in still water and in a current field, see for instance Ref. 2. The importance of the coupling terms due to the combined modes of motions, however, is not known.

By means of a lf large stroke mechanical oscillator prescribing combined motions on the tanker hull the coupling terms were investigated in still water and in current. The results will be presented in the paper.

Introduction

In order to compute the lf motions of a moored tanker the equations of the lf motion have to be established. Most of the maneuvering models are based on the model as for instance presented by Abkowitz, Ref. 3. In this model the maneuverability is described by means of linear and nonlinear derivatives of the hydrodynamic forces and moments by perturbation models.

Contrary to normal maneuvering applications (high speed, high rate of turn and relative small drift angles) specific requirements have to be fulfilled for a moored tanker e.g.:large drift angles (0-360 degrees)small values of drift velocities (combined low frequency tanker motions in still water or in a current field)small values of oscillating rate of turnrelatively large transverse motionsin steady state in a current field the hydrodynamic forces have to correspond with the steady current loads.

These requirements do not satisfy the model of Abkowitz. The full equations of the lf motion as applied for a moored tanker in still water and in a current field should be established. A present formulation is presented. Starting in an ideal and irrotational fluid the equations of motion as given by Norrbin (Ref. 4), taking into account the Munk-moment (Ref. 5) can be established. In real fluid, however, viscosity is involved. The viscosity modifies the Munk-moment and introduces additional resistance forces (d'Alembert paradox).

By means of model tests using a lf large stroke oscillator the viscous forces in the separate surge, sway and yaw modes of motion can be determined. A comprehensive description is given in Ref. 2.

Moored tankers in general, however, perform fish tailing motions. A fish tailing motion consists of a combined motion in the horizontal plane.
Seismic Repeatability Benchmarks
Authors: Grion Sergio , Keggin James , Ronen Shuki , Caldwell Jack
Published: October 2008

The effects of various parameters on repeatability can be considered in making decisions on acquisition and processing parameters. For this reason we apply repeatability benchmarks based on the RMS difference of two data sets to various repeat marine seismic data. The datasets considered here come from two different areas, Foinaven and Viking Graben. We have two vintages of 3D Streamer and OBH data from Foinaven ('95 and '98) and 2D multi-component data, with and without cable redeployment, from Viking Graben.

The repeatability study of these data sets provides quantitative measurements of the effects of acquisition parameters, data processing and survey matching methods.

Introduction

The oil and gas industry is using various types of time-lapse seismic data for 4D analysis to monitor reservoir changes. The most common data type is surface towed streamer data, which may have inconsistent parameters between base and monitoring surveys. Another type of time-lapse data is from seabed sensors.

We apply the NRMS (Normalized RMS) repeatability benchmark to various repeat marine seismic data sets. This benchmark is based on the relative difference between each of two compared data sets. Another often-used repeatability benchmark is Predictability (Ref. 3). In this paper NRMS is computed at various steps of a matching procedure during which the amplitudes of each pair of data sets are matched and phase and time shifts between the two data sets are compensated. NRMS is evaluated both in the time and frequency domains, to determine the effects of acquisition and processing parameters both globally and for different frequency bands. Besides NRMS, for time lapse survey design the needed parameter is the Noise to Signal Ratio (NSR); NSR should be lower than production effects on seismic data. We estimate NSR from Normalized RMS.

Repeatability benchmarks

The repeatability benchmark used here are based on the RMS difference of two data sets normalized by the average RMS energy of the two parent data sets. We call this benchmark Normalized RMS (NRMS). Given two data sets A and B, NRMS for traces aj and bj would be:

Mathematical equation (1) (Available in full paper)

where j denotes trace location and i time samples, i=1,...,Nt.

The lower bound of the NRMSj is of course zero in the case that aj = bj. The upper bound is 2. If traces ajj and bj are not related, but have the same average amplitude, it can be shown that the expected value of the NRMS is ?2.

Once NRMS is computed, it can be shown that the Noise-to-Signal Ratio (NSR) is:

Mathematical equation (2) (Available in full paper)

This expression for NSR is strictly valid only if in data sets A and B noise has the same variance and signal has the same power. NSR tends to infinity when the two data sets are made of random noise and is 0 when data sets A and B are equal.

Equations (1) and (2) are computed in the time domain but NRMS and NSR can also be computed in the frequency domain, applying (1) and (2) to the Fourier transform of ajj and ajj.
Marine Challenges Encountered by a Small Mine on the Maine Coast
Authors: Beck Frederick M.
Published: October 2008

Callahan Mining Corporation is currently mining copper and zinc ore from an open pit mine on the edge of Penobscot Bay in Marne. The open pit occupies an area once largely covered by a salt water pond. The mining operation utilizes conventional mining and milling techniques and in this respect perhaps could not be considered a true marine mining operation. However, many obstacles had to be overcome due to the proximity of the ocean beforethe mine could be brought into production. Problems with which inland mines do not have to contend are faced daily. These include effluent control, marine mud stability, salt water encroachment, reclamation, and exploration.

The ore deposit stratiform massive sulfide body in early Paleozoic volcanics. The principal ore minerals are sphalerite and chalcopyrite with minor galena. Associated minerals include chlorite, talc, and carbonate. The deposit was discovered in 1880 at low tide by a clam digger. Surface ore outcrops were entirely below high tide. The mine was developed and mined from three shafts. Apparently the deposit became unprofitable in about 1887. A re-evaluation in 1964 by the Callahan staff prompted the present open pit operation. Production is currently at the rate of 700 tons per day.

Exploration for additional are deposits is complicated by the presence of saltsaturated mud in estuaries and salt water covering geologically favorable prospecting ground. Many conventional inland exploration techniques are useless near these areas.

The ocean presence has added substantially to the mining costs, thus narrowing the profit margin. New techniques must be developed by the mining industry to cope with oceanographic problems. Some of thesechallenges are being met at Cape Rosier and can be applied to future mining ventures faced with similar marine problems.

INTRODUCTION

The Penobscot Mine on the Maine coast is not a "marine mining" operation in the strictest sense. For the most part, conventional techniques of mining and milling are in use and the ocean is a nuisance. However, by being located at the sea-land interface, there are a number of factors which influence the operation which would not be encountered inland. The engineering chal1enge of dealing with the shallow estuary were relatively easily mastered. The challenge to mineral exploration still exists and is a subject of continuing effort. The nation's sea-land interface is probably one of the most popular and valuable multiple use areas in the country. In Maine it has scenic beauty, is sought after for summer homes, provides food and shelter during parts of the life cycles of innumerable marine species, and is the basis for commercially important coastal fisheries. It is an area high on most lists for environmental protection. It is natural that the addition of another "user" to this area would be resisted, particularly when that user represents an industry which has a past record of environmental abuse.
General Characteristics of Currents in the Deepwater Gulf of Mexico
Authors: DiMarco S.F. , Reid R.O. , Jochens A.E. , Nowlin W.D. , Howard M.K.
Published: October 2008

Currents were generally surface intensified, with speeds reaching ~200 cm/s in association with energetic events such as passage of a Loop Current Eddy or intense atmospheric storm. A minimum in current speed occurred at about 800-1000 m depth. But maximum speeds can reach 120 cm/s at about 2000 m. Bottom intensification was present. Horizontal spatial decorrelation scales were smaller in the transverse direction than longitudinal.

Introduction

Over 8 million hours of current records were assembled as part of the Gulf of Mexico Deepwater Physical Oceanography Reanalysis and Synthesis of Historical Data Study, sponsored by the Minerals Management Service (MMS). Data assembled were from the area bounded by the shelf edge (approximately the 200-m isobath) of the northern Gulf of Mexico and the 25°N latitude line. Data extended from the sea surface to the sea floor in water depths from 200 m to over 3000 m. Additionally, a seven year (1993-1999) circulation model run was completed using the high-resolution University of Colorado Princeton Ocean Model (CUPOM) for the Gulf of Mexico1. Current records and the output of the CUPOM run were examined to characterize currents and estimate horizontal scales of deep flow in the Gulf of Mexico.

Results

The characterization of the currents was examined using the observational data base. Because of a lack of concurrent observational data with adequate spatial resolution, the horizontal scales were estimated using the CUPOM output for 1993.

Observations.

All current records of good quality were compiled to show the percentage of time that unfiltered currents exceeded various speed thresholds as a function of depth ranges. Because currents below about 800 m in the Gulf generally are nearly barotropic, and because deep observations are scarce, we used the large depth range of 1200 m to the sea bed to obtain a reasonable sample size for the deep layer. Results indicate that currents above 200 m exceed 75 cm/s about 2% of the time and 100 cm/s almost 1% of the time. The fastest currents are near surface and percents for all speed bins decrease rapidly with depth above 800 m. Currents below 800 m are normally rather coherent in the vertical, sometimes with bottom intensification. Below 1200 m the currents exceeded 40 cm/s about 0.6% of the time, which is greater than for the depth interval of 800–1200 m; this is evidence of bottom intensification.

For each current record, a current rose and persistence table were produced. These can be examined to study the effects of energetic current events, such as occur with passage of the Loop Current, associated eddies, or hurricanes and other intense atmospheric storms. For example, mooring I1 was deployed for MMS in water depth of 2001 m in the northcentral Gulf just south of the Sigsbee Escarpment.
Visualization of Oil, Gas, and Water in the Subsurface
Authors: Anderson Roger N. , Boulanger Albert
Published: October 2008

Tracking the flow of oil, gas, and water in real-time while reservoirs are being drained is now possible through the emergence of rugged downhole sensors, the Internet, high bandwidth satellite and fiber communications and rapid middleware wrapping of software applications. The question is what information delivers economic return on the investment required. The good news is that all along the value chain, prices are coming down because of commercial pressures from outside the energy business. For example, Direct PC will likely drop the cost and increase the bandwidth of satellite communications to remote locations by an order of magnitude over the next few years.

Application

The manufacturing process by which we produce energy is being reinvented like we have never before experienced in this business. The oil and gas field of the future will be part of a much larger Information Technology (IT) network. Each field will be a wired, internet-connected, real-time monitored, remotely controlled, electronic venture. Each well, pipeline, rig, production platform, compression facility, and even the pumpers themselves, will have a IP (Internet Protocol) address. Any browser on any laptop in the company (with proper password protection) can log onto the myoilcompany.com URL at any time of the day or night -- from anywhere in the world -- and visualize production, well test, logging, and other real-time measurements coming from the 4D monitoring of field performance.

Results and Observations

However, there are fundamental reasons why such an integrated IT system for the oil and gas field is a difficult mission for the energy industry to pull off successfully. Principal among them is that the "last mile," as it is called in the communications industry, (the field connectivity to the manufacturing facility itself) is about as difficult an IT environment as could be imagined. Other IT savvy manufacturers around the globe also deal with multiple vendors, millions of customers, and millions of parts as we do, but our SITE of manufacture of energy products is NOT usually in a metropolitan area with communications infrastructure in place. Instead, it is found in whatever water depth or remote geography (usually rural) the oil and gas happens to be discovered beneath. And then, of course, the "very last mile" to the resource itself is under the ground and cannot be visited, or even imaged clearly.

Not only must energy companies deal with a constantly changing set of IT vendors and bandwidth constraints from field to field, but each must be specified from the start to operate continuously for 30+ years, as part of an internetconnected portfolio. In the future, oil and gas fields will form an information grid with other fields, pipelines, land, and seaborne traffic, refineries and storage facilities, etc. that form the complete enterprise of the company (Figure 1).
Vortex-Induced Vibration and Design of Pipelines in Deepwater
Authors: Chaudhury Gautam
Published: October 2008

Field developments in remote areas of deep water offshore require the services of long distance pipeline systems. Design and installation of pipelines in deep waters are expensive. Seabed terrain in deep water is rough and more numbers of unsupported spans of long lengths are expected. Design against vortex induced vibration (VIV) is of concern for the reliability and cost of deepwater pipelines.

The practice of design against VIV has been to limit allowable span lengths such that onset of VIV cannot be initiated. This is a highly conservative approach resulting in expensive span corrections. Probability of occurrences of current velocities at seabed reaching critical is very low, hence, it is proposed that the designs be based on actual fatigue damage. This is also recognized by DnV Guideline 14 (June 1998).

Existing methods of VIV response calculation produce extreme response, which leads to conservative fatigue damages. Based on a non-dimensional analysis and fitting model test results an empirical relation, as a function of Reynold's number, reduced velocity, and reduced damping, is proposed. The formula determines equivalent response, which represents overall fatigue accurately.

Introduction

Offshore pipelines transport reservoir fluid from wellhead to production platform and produced oil and gas from platform to shore terminal. It is one of the most important and expensive items of an offshore field development project. It is even more expensive for developments of fields in deep waters. The sea floor terrain is rough in deep waters, consequently, unsupported spans are large and more in numbers. One of the major elements of cost in offshore pipeline system is the span correction and quite often correction of spans are required to satisfy the design against vortex induced vibration (VIV).

Classification notes (DnV) are available explaining the principles and procedures of VIV, but until recently (June 1998) there was no regulatory guidance on the design of unsupported pipe spans against VIV. Even after the introduction of the DnV Guideline No 14, normal design practice has been to limit the length of a span in such a way that the natural frequency of the pipe is away from the shedding frequency of the vortices such that no resonant vibration can take place. Reduced velocity for no onset of inplane vibration is small. This means small allowable free span and costly remedial measure for longer spans.

The major drawback of the present design practice is that it is unreasonably conservative. It does not consider the magnitude, duration, and the combined damaging effect of the VIV in relation to the available resistance to fatigue damage of the pipe line structure. Current velocities at the seabed are mostly small and negligible. The probability of seabed current velocity reaching critical is extremely low and, therefore, a realistic approach to design a pipe span would be to design it against fatigue, like other submerged structural members are designed against wave induced fatigue.
Gas Hydrate in Seafloor Sediments: Impact on Future Resources and Drilling Safety
Authors: Dillon William P. , Max Michael D.
Published: October 2008

Gas hydrate concentrates methane and sometimes other gases in its crystal lattice and this gas can be released intentionally creating a resource or escape accidentally forming a hazard. The densest accumulations of gas hydrate tend to occur at sites where the base of the gas hydrate stability zone (commonly the upper several hundred m of the sedimentary section) is configured to trap gas, often as a broad arch. The gas may rise from below or form by bacterial activity at shallow depth, but gas commonly is concentrated near the base of the gas hydrate stability zone by recycling. This gas accumulates in presumably leaky traps, then enriches the hydrate above as it migrates upward by diffusion, fluid movement through sedimentary pores, or flow along fracture channelways. Analysis of seismic reflection profiles is beginning to identify such concentrations and the circumstances that create them. The first attempt to explore for gas hydrate off Japan by the Japanese National Oil Corporation produced quite favorable results, showing high gas hydrate contents in permeable sediments. Gas hydrate dissociation can be a safety concern in drilling and production. The volume of water and gas released in dissociation is often greater than the volume of the hydrate, so overpressures can be created. Furthermore, the gas hydrate can provide shallow seals, so the possibility of high-pressure flows or generation of slides is apparent.

Introduction

The gas-bearing, ice-like form of water known as gas hydrate or gas clathrate occurs in abundance in marine sediments and stores immense amounts of methane, with major implications for future energy resources and seafloor stability. Gas hydrate forms wherever appropriate physical conditions exist - moderately low temperature and moderately high pressure - and the materials are present - water and gas near saturation in the water1. These conditions can be found in the deep sea, commonly at water depths greater than about 500 m or somewhat shallower depths (about 300 m) in the Arctic's colder water. Like ice, crystalline methane hydrate is less dense than water, so if hydrate forms in the water it floats upward and breaks down (dissociates) at lower pressures and warmer temperatures. However, if the gas hydrate forms within sediments, it is bound in place. Gas hydrate can exist in a zone (the gas hydrate stability zone - GHSZ), that extends from the seafloor down to a depth where the temperature has risen sufficiently to make hydrate unstable (even though the pressure increase that comes with greater depth will increase gas hydrate stability). The base of the GHSZ ranges from just below the seafloor to several hundred to a thousand meters below it at greater water depths (higher pressures).

Gas hydrate in ocean sediments is mostly (99%) formed of biogenic methane, but significant amounts of thermogenic gas hydrates that include higher carbon-number hydrocarbons exist in active petroleum areas (e.g. Gulf of Mexico, Caspian Sea).
Estimates of Worldwide Gas Hydrate Resources
Authors: Lerche Ian
Published: October 2008

Gas hydrates have been touted as the next generation of energy resources exploitable for commercial gain and anthropogenic use. It would then seem relevant to estimate the potential resources available in order that one has an appreciation of availability. Several such estimates have been made over the years for both onshore and offshore gas hydrates. This paper examines the relative percentages and the ranges of uncertainty for both the onshore and offshore estimates. In addition, the estimated resources are plotted versus the year in which the estimate was made to see if any convergence of results is being achieved with time as more data become available.

The main conclusions are that there seems not to be any systematic pattern of convergence of resource estimates with time, nor does there seem to be any narrowing of the uncertainty of the estimates for either onshore or offshore resource estimates as more data have become available over the last twenty years. It would seem that a concerted effort is needed to improve estimates if there is to be any hope of assessing the commercial worth of hydrate resources and of deciding whether hydrates really do represent a significant exploitable energy resource on a worldwide basis.

Introduction

As a cleaner energy source than hydrocarbons, gas hydrates have often been advertised as an appropriate alternative. The fundamental question is whether there is a sufficient resource of gas hydrates, on a worldwide basis, to act as a dominant energy source for the future. To be sure there are also technical problems of extraction and production of hydrates, once found, be it in the onshore or offshore regions. But the technical and commercial risk problems are secondary in the sense that unless there is a sufficient worldwide resource of gas hydrates, then technical methods will not be developed to exploit a constrained limited resource. There would be no profit in so doing. Likewise, even if technical extraction methods already existed, there would be no worldwide xploitation of gas hydrates if the costs of involvement and recovery were to rise to a point were no profit could be made-much as happens with oil and gas fields today, which are often not produced because of too high a cost relative to potential gains.

So the sine qua non is to first estimate the resources available. Indeed, this aspect has been recognized as the ultimate driver of potential further developments for over twenty years now (Kaplan, 1974). And, as new information has become available over the years, such has been incorporated in estimates of worldwide resources of gas hydrates both onshore and offshore. Since the early 1990's, after the dissolution of the Soviet bloc, much information has become available that heretofore was the exclusive province of the Soviet Union and/ or the intelligence gathering agencies of the world - most notably the CIA in America.