bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Technique for Rapid Estimation of Fracture Closure Stress When Using Propellants
Authors: Cuthill D. A. , Schatz J. F. , Gilbert J. V.
Published: December 2007

Minifracs are used to assist with main hydraulic fracture design by generating estimates of the fluid efficiency, closure stress, fracture geometry, and leakoff coefficient prior to the main treatment. Closure stress is frequently determined by analyzing the pressure falloff response after pump shut-down using a Nolte G-Function analysis plot. Comparison of the measured data with the dimensionless Nolte G time indicates closure when used in combination with the derivative and pressure superposition derivative.

During perforating/propellant treatments of wells, the use of a high-speed downhole digital pressure data recorder enables a new rapid technique for determining closure stress using the G-Function and associated methods. The propellant event breaks down the perforations and extends fractures into the formation in the time span of tens of milliseconds, and can thus be treated as a high-speed minifrac. The analysis method and feasibility of this new technique are demonstrated.

The falloff pressure curve after a propellant event, typically lasting no more than a few hundred milliseconds, is shown in several case histories to provide sufficient closure information. Where these data are available, results are consistent with other methods. Although certain favorable conditions must exist for the method to be applicable, this new technique can be used where a quick estimate of closure stress is needed prior to hydraulic fracturing and while equipment is in place in the field. Work continues to fully define the range of applicability and accuracy of the new technique.
Increasing Leakoff Pressure With New Class of Drilling Fluid
Authors: Santos Helio
Published: December 2007

A new class of drilling fluid has been developed and proved to be extremely effective in increasing the leakoff pressure in permeable formations. A simple laboratory test is described to assess the limits of potential increase of leakoff pressure in the field. This paper describes some fundamental issues regarding fracture and leakoff pressures for well construction purposes and then shows how the increase in leakoff pressure can be achieved with the use of this new drilling fluid. Some case histories are presented in which the fluid has proven to increase the leakoff pressure effectively, and a comparison is made with drilling fluids traditionally used, highlighting the limitations of the current fluids to effectively deliver what the industry really needs. Several applications are presented in which an increase in leakoff pressure can hugely reduce the costs and risks of the wells.
Evaluating the Appropriateness of Intelligent Completion Technology - A Case Study in a Shallow Clastics Gas Reservoir
Authors: Bhat Suniti K. , Thomson Andrew W. , Sarkar Radheshyam , Mohd-Nor Norlizah , Huang Edmund
Published: December 2007

In recent years, the deployment of intelligent completion technology has increased as has the range and functionality of the systems available. The focus has been on developing intelligent completions that will allow a greater degree of controlling reservoir inflow. Improvements in the methods that could be used to model the values of these complex completions have in general lagged behind. In this paper, a phased process for evaluating the productivity benefit offered by an intelligent completion system for a multi-layered, shallow gas reservoir system is described in detail.

To start the process, an intelligent completion system was selected that was compatible with the well architecture and would provide maximum flow control capability (infinitely variable choke). Analytical methods where then used to conduct a screening exercise in order to evaluate the production benefit this high-end intelligent completion could offer. This screening exercise provided a fuller understanding of the hydraulic interactions occurring within the wellbore. As such, it was possible to tailor the level of intelligent completion functionality to the production benefits derived. A detailed study was then carried out using dynamic 3D-simulation modelling, which incorporated the selected intelligent completion components as a part of the reservoir simulation.

This phased approach helped in determining the optimum intelligent completion configuration taking into account the time related reservoir performance changes.
Locating 3D Wells in Deep Offshore Channel Reservoirs Using High Resolution Seismic Data and Reservoir Model: An Example from the Rosa Lirio Project
Authors: Verdière S. , Guyotte E. , Verpeaux J. -F. , Gazaniol D. , Clavel J.
Published: December 2007

The development of Oligocene deep offshore turbidite channels has begun in Angola Block 17 with the Girassol field. Jasmin, RosaD, Rosa E, Cravo and Lirio are additional reservoirs in the same setting, for which subsea development is also planned.

Conventional 3D seismic, although fit for exploration purposes, has not adequate resolution to take into account the heterogeneities suspected in turbidite channels and shown by the well tests. To overcome this shortcoming, High Resolution seismic has been acquired. The images presented, coming from the interpretation process, show spectacular results. The identified heterogeneities result in a good match between the model and the well tests.

Detailed interpretation has been input in a deterministic way in the reservoir model. For instance, sand juxtaposition along the faults, seismic facies units, lateral and vertical connectivity and potential barriers have been analysed and represented. The resulting connectivity within the channelled reservoirs appears complex and its interpretation required combining deterministic picking and more automatic approaches. Highly integrated work between geologist and reservoir engineer results in a refined geological description that enabled initial well targets to be defined.

Heterogeneities that may result in by-passed oil are accounted for at this stage in the completion and selectivity philosophy. The well pattern must also be consistent with the drilling constraints and the location, type and number of subsea manifolds. Optimisation of the well pattern needs to consider these aspects in conjunction with the geology. This is achieved through multidisciplinary teamwork with a fully integrated software.

In such a channelled deep offshore context, the challenge of development well definition can be overcome thanks to early identification and consideration of the most influential parameters. Understanding and compromises within the integrated team are the underlying keys to obtain coherency between the sub-surface and surface constraints.
Tertiary Miscible Gas Injection in the Alwyn North Brent Reservoirs
Authors: Burns L. J. , Richardson G. J. , Kimber R. N.
Published: December 2007

The Alwyn North complex is located in Block 3/9a of the Northern North Sea, UK sector. Production commenced in 1987 from the Middle Jurassic Brent Group, and was supported by water injection from early 1988. In 1997 a Tertiary Miscible Gas Injection project was sanctioned with incremental reserves for the four main reservoir panels, estimated at 33Mboe. This figure includes a waterflood phase post MGI and field depressurisation, and was evaluated against a continued waterflood scenario.

Gas injection commenced in late 1999 into the Brent East-South panel followed in September 2000 by injection into the Brent North West panel. The early part of the project was interrupted by facilities difficulties, however by mid 2002 1.68Gsm3 of gas had been injected.

In the 2 1/2 years since first injection, incremental oil has been observed in four wells showing between a 2 to 10 fold increase in oil potential. Associated gas breakthroughs have been experienced in 2 of these wells and can be related to zones of high permeability. A positive correlation can be seen between the gas injection rate and the oil production potential and by 2 1/2 years into the project around 1 1/2 million bbl of incremental oil had been recovered. Ensuring voidage replacement is maintained is key to the success of this project with average reservoir pressures only marginally higher than Minimum Miscibility Pressure.

Intensive reservoir monitoring (permanent downhole gauges, wellhead pressure & temperature data, tracers, production logging, fluid sampling and regular well tests) has been fundamental to improving the understanding of field performance. This information has been regularly integrated into full field geological and compositional simulation models to optimise the near term performance of the panels and to plan the future strategy.
Liberal Art College Graduates - A Promising Source Of Drilling Personnel
Authors: Wilson L.
Published: December 2007

A large international drilling contractor was faced with a severe shortage of promising new employees to fulfill its needs and help provide for further growth. A whole new source of entry level personnel were hired from among liberal arts college graduates. After indoctrination they were sent to overseas assignments, and the results of the 4 1/2 year old program are summarized in the paper.

BACKGROUND OF PROBLEM

It has been documented in many places that there was a huge increase in drilling activity both in the U. S. and overseas during the early 1970's. The resulting shortage of skilled drilling personnel became acute at that time and has personnel became acute at that time and has remained somewhat critical since that time. As a result, there has been a proliferation of recruiting activities as well as intensive training programs of one sort or another. programs of one sort or another. In the case of SEDCO, Inc., the shortage of U.S. personnel was compounded because:We had no U.S. based operations to serve as a training facility.The equipment with newer rigs demanded more technological knowledge.Most nations demand that training be done with their own citizens rather than U.S. citizensLanguage aptitude became much more important than ever before.Any U. S. citizens had to be raised to a skill level acceptable to the various governments overseas.

With this background we recognized that the shortage was not only in quantity but in quality, so we determined to search for a whole new source of people who could help sustain our growth both from a standpoint of rig count and quality.

SELECTION OF LIBERAL ARTS GRADUATES

In the beginning we considered the high school graduates who formed most of the skilled drilling personnel pools of today and had to reject them as a source for new people. One of the principal reasons was that the high school graduates of today tend to have a multitude of opportunities that will keep them near home, and, of course, for an overseas assignment they tend to be somewhat immature and certainly not prepared to deal with foreign nationals. Even if prepared to deal with foreign nationals. Even if they met the criteria of supplying the quantity needed the quality was sadly lacking since they had no demonstrated ability to learn at a rapid rate.

We next considered junior college graduates who mostly have taken vocational courses, such as diesel mechanics, etc. The graduates of such institutions seemed ideally suited for careers in the drilling business and satisfied essentially all of the requirements we had.
A New Approach for Reservoir Characterization
Authors: Aminian K. , Thomas B. , Ameri S. , Bilgesu H. I.
Published: December 2007

To reliably predict the reservoir performance, an accurate model of the reservoir is necessary. For reservoir simulation purposes, the flow unit model is most practical approach. The flow units are defined according to geological and petrophysical properties that influence the flow of fluids in the reservoir. Identification and prediction of flow units are strongly dependent on the availability of permeability distribution. This need for permeability distribution significantly limits the identification of flow units in reservoirs where permeability measurements are not abundant such as most reservoirs in the Appalachian Basin.

In this study, statistical and artificial intelligence techniques were employed to identify flow units based on limited data obtained from core analysis supplemented by mini-permeameter measurements, geological interpretations, and well log data in a heterogeneous oil reservoir in the Appalachian Basin. An innovative methodology was then developed to predict flow units using only well log data. The distribution of flow units in the reservoir was then predicted based on abundant well log data. Finally, permeability and porosity distributions were predicted based on the distribution of the flow units in the reservoir. This approach led to development of a reliable reservoir model. The accuracy of model was verified by successful simulation of the production performance. The methodology presented in this paper can serve as a new guideline for the characterization of heterogeneous reservoirs.
A Theoretical Model Of The Polymerization Of Silica In Aqueous Media
Authors: Peck Lawrence B. , Axtmann Robert C.
Published: December 2007

Despite three decades of experimentation, no general, quantitative description of the polymerization of silicic acid in aqueous solutions has emerged. An accurate mathematical model could have a seminal effect on the solution of many problems in the utilization of geothermal resources, e.g., in the prevention of silication in boreholes, energy conversion equipment and reinjection wells. In addition, such a model might advance understanding of hydrothermal alteration in geothermal reservoirs.

We report here an analysis that divides the overall reaction into successive regimes that are limited in rate by nucleation; chemical reaction; and diffusion of monomer to growing polymer particles.

In the case of homogeneous nucleation, an analogy with the theory of condensation suggests that RN, the rate of formation of critical nuclei, isEquation 2

where Î3 and Vo are the surface tension and specific volume of the solid, respectively; S C/Ce where C is the concentration of monomer and Ce is its solubility; and A is a constant. Exploration of the properties of equation (2) leads to the prediction of maxima and minima in the polymerization rate as a function of temperature and of the temperature-dependent induction times that have been observed in the laboratory and in nature.

The dimensionless ratio rfko/D serves as a useful index of whether diffusion or chemical reaction exerts the dominant influence over silica particle growth. rf is a characteristic length; ko is the surface specific, forward, rate constant; and D is the monomer diffusivity. For rfko/D 1, the reaction rate is very rapid, diffusion is limiting, and particle growth is described byEquation 36

where Rp is the particle radius divided by rf; Co=Ciâ?'Ce, where Ci is the initial monomer concentration; and Ï? tD/rf2.

In the chemical reaction-limited regime, rfko/D 1 and the appropriate solution becomesEquation 42

For both diffusion-limited and reaction-limited regimes, the relationshipEquation 37

holds and allows the calculation of C vs. time from equation (36) or (42).

The agreement between theory and extant laboratory data on natural and synthetic silica solutions is excellent. The analysis indicates, moreover, that a priori evaluation of the ratio rfko/D would permit the wily experimentalist to avoid diffusion limitations whilst attempting to measure chemical kinetic rates.
Performance of One of the Iranian Carbonate Reservoirs
Authors: Jamshidnezhad Mohammad
Published: December 2007

More than ninety percent of Iranian petroleum reservoirs are carbonate. In order to investigate Iranian petroleum reservoirs, one of the Iranian carbonate fields has been analyzed. This field is located in Southern Iran with 23 km long and 7 km wide, and contains two reservoirs,I1 and II2.One of these reservoirs sits over another and an impermeable zone separates two reservoirs. In this field, horizontal and directional drilling have been experienced. Production from this field was started 10 years ago,and it is estimated for naturally depletion 80 years must be considered.At the present,out of 28 drilled wells,6 wells are horizontal,7 wells are directional,and 15 wells are vertical.Except one well,all horizontal wells are on stream.Average daily rate of horizontal and directional wells respectively are about 3.1 and 3.5 percent of overall field rate.Nevertheless,in this field and other Iranian carbonate field,there are numerous problems for horizontal wells,such as high losses of drilling mud,troubles in petrophysical logging,need to high cost and time.

In this paper, after investigating geological studies,PVT, static pressure,well testing experiments,performance of horizontal,vertical and directional wells and overall performance of this field,the ways for rate increasing have been proposed.As far as possible,wells be drilled vertically(especially in second reservoir,II2) and horizontal drilling be done only in first reservoir,I1.Also,using of artificial lift (such as installation of electrical submersible pumps in wells) is recommended.
Real Time, Real Fast: Drilling Horizontal Wells in a Heavy Oil Environment
Authors: Balke Scott C. , Rosauer Mark S.
Published: December 2007

The presence of producible hydrocarbons in Orinoco Tar Belt of Eastern Venezuela was confirmed as early as 1936. Today this accumulation is thought to contain more than 1.2 trillion barrels of heavy and extra heavy oil in a giant stratigraphic trap 320 miles long by 40 miles wide. Even though this region has a tremendous volume of oil it has remained marginally cost effective to produce due to the significant costs of development. Using the latest technology and innovative techniques the Hamaca Project, centrally located in the Orinoco Tar Belt, will be able to effectively and economically develop a portion of these reserves.

The Hamaca area covers some 250 square miles and Petrolera Ameriven has a commitment to develop and produce the 165,000 acres defined under the association agreement at a rate of 190,000 BOPD for the life of this project. The oil, when cooled and degasified, resembles more a tar or asphalt that one would use to pave a road than the oil you would put in your crankcase. Adding to the complexity of this project is that the major reservoirs within the field were deposited in major low stand and transgressive systems tracts, comprised of meandering fluvial to fluvial-tidal deltaic deposits.

Hamaca utilized a system of LWD, satellite links, continuous updating and real-time visualization to assess and mitigate risks while drilling. This system allowed extremely accurate placement of the shoe in the build sections, for real-time directional control in the laterals and has multi-rig capability allowing for better utilization of resources. Some examples of the situations encountered and their remedies were: the identification of sand/shale interfaces and the redirection of the bit, non-pay zones were identified and avoided and planned well paths revised to encounter better pay.

The methodologies developed along with the technology used were effective in minimizing developmental costs that greatly enhanced the financial viability of the project.
The Effect of Clay Fraction on Heavy Oil Depletion Test
Authors: Andarcia L. , Kamp A. M. , Huerta M. , Rojas G.
Published: December 2007

Primary production of heavy oil from unconsolidated sand reservoirs is a process that is not well understood. Laboratory depletion experiments of sand packs, which mimic the field situation at a laboratory scale, show that production behavior of heavy oils under solution gas drive depend in a complex way on diverse parameter such as: depletion rate1,2, fluid properties 3, porous medium properties45, etc.

This work focuses on understanding the effect of the clay fraction in the sand pack on the recovery process. Experimental results from depletion tests at constant total volumetric production rate are presented. The porous media consisted of synthetic sands with different proportions of clay, except for one of the experiments, where reservoir sand was used. The oil was extra heavy crude (8 ºAPI) from the Venezuelan Orinoco Belt.

Pressure, pressure drop over the core, and oil and gas production were measured as a function of time. It was found that critical gas saturation and recovery factor increase with increasing clay content, whereas the supersaturation or the deviation from thermodynamic equilibrium decreases. This is interpreted in terms of an increasing number of nucleation sites at increasing clay concentration. More activated nucleation sites lead to more and smaller bubbles that allow a lesser mobility for the gas phase. Gas then becomes significantly mobile at larger gas saturations. This hypothesis is supported by previously published data from micromodel experiments doped with clay particles6.

The fact that critical gas saturation and recovery factor depend on the composition of the reservoir sand may strongly affect the evaluation of reservoir production capacity, because large regional heterogeneities related to clay content are often present in oil-producing "sands".
Dynamic Fracture Modelling Approach for Cold Lake Cyclic Steam Stimulation
Authors: Lebel J. Pierre
Published: December 2007

In Imperial Oil’s Cold Lake field, Cyclic Steam Stimulation (CSS) is used to recover bitumen from the Clearwater formation. At initial reservoir conditions, fluids are essentially immobile due to high bitumen viscosity and due to very low relative permeability to water. The injection of steam is achieved by injecting at pressures that induce hydraulic fractures in the formation. Numerical simulation techniques typically handle fracturing by imposing a large increase in permeability as the pressure exceeds a fracture pressure.

Standard simulation approaches using an ExxonMobil in-house simulatori to modeling fracturing require an excessive pressure gradient in order to propagate a fracture. As a result, the pressure of the fracture blocks is overestimated, resulting in an unrealistic overestimate of leak-off from the fracture. The fracture area is thereby significantly underestimated and possible fluid communication between wells is not properly modeled.

The term "dynamic fracturing" refers to an approach that improves hydraulic fracture modeling by using a variation of upstream weighting to calculate the effective permeability between fracture blocks. The upstream weighting is done indirectly using changes in void ratio, which is a measure of pore dilation due to pressure change. The method has been calibrated with field data from two Cold Lake pads.

Early attempts to use this method encountered numerical stability problems. This resulted in very slow run times, and in many instances, cases could not be completed. The method has been improved using a simple dampening scheme making it practical to use in multi-well models. This approach is aimed at improving predictions of fluid distribution in early cycles of CSS including predictions for infill well performance. More realistic fluid communication modeling improves subsequent infill performance predictions. Useful comparisons of performance from different steam strategies require good predictions of fluid distribution caused by each strategy. This work has imporved our ability to model the CSS process and to predict field behaviour.
Certification Of The Heather Platform
Authors: George Philip John , Sladden Peter Richard
Published: December 2007

This paper describes the results of foundation analyses carried out by Lloyd's Register of Shipping as part of its independent appraisal of the Union Oil Company Heather platform, which was installed in the North Sea in 1977. The studies described were made in partial fulfillment of the requirements incorporated in the 'Offshore Instalations (Construction and Survey) Regulations'1 for the issue of a Certificate of Fitness.

The paper discusses the validity of using currently accepted empirical design methods of predicting pile capacity and behaviour in the very hard boulder clays encountered in the Heather field. The results of tests on boulder clay from other sites both on and offshore are compared with the Heather soils.

Introduction

The very hard boulder clays found in the Heather field and at other locations in the North Sea have presented problems to platform designers insofar as the undrained shear strengths are beyond the range of those normally experienced onshore. This brings into question the commonly used relationships of undrained shear strengths with ultimate capacity and stress-strain relationships.

The paper compares the behaviour of similar boulder clays from onshore sites and from other North Sea locations and makes use of the derived relationships in the soil/structure interaction models.

The analyses presented consider:the interaction of the piles within the pile group using boundary element methods, and assuming an equivalent three-dimensional elastic continuum;the interaction of piles with the structure using two-dimensional non-linear finite element analyses.

In addition, a pile axial load transfer analysis is discussed which assumes non-linear load deflection characteristics and compares the Heather foundation behaviour with pile load test data from the B.P. West Sole field.

The primary objective of the analyses discussed is to establish the loads and deformations within the foundation, and to provide the pile load response relationship to be utilized in the superstructure analysis.

A companion paper by Durning et al (1978)2 describes in detail the foundation design history and site conditions.
Predicting Pile Driveability: Heather As An Illustration Of The "Friction Fatigue" Theory
Authors: Heerema Edward P.
Published: December 2007

In the series of papers on the Heather Field pile foundation, this paper presents the backgrounds of the driveability prediction made by Heerema Engineering Service. The prediction was made according to the 'friction fatigue' theory, which is based on the assumption that skin friction in clay is gradually lost along the pile shaft as driving proceeds.

A laboratory test is described which illustrates this phenomenon.

A mathematical model is given for the shape of the horizontal stress distribution along the pile shaft; parameters needed in this formulation have been empirically determined, partly from laboratory tests and partly from computer post-analyses of driving experiences. This was necessary as it is as yet net possible to quantify horizontal soil stresses acting on the pile wall during driving on an analytical basis.

The friction fatigue theory presented here proves to be consistent for all pile driving experience in stiff and hard clay in the North Sea investigated by the author, and it is believed, therefore, that it will in general lead to improved pile driving predictions as compared to other available methods.

1. Introduction

Pile driving at Heather Field was one of the most interesting piling cases of the past few years in the North Sea. The soil consisted of very heavily overconsolidated clay at shallow depths, with undrained shear strength values up to 800 KN/m2, twice the values encountered so far in the North Sea.

At depths near to design penetration of the piles, however, the clay had rather common shear strength values.

It was therefore difficult to make a reliable prediction of the driveability. By conventional means of predicting (i.e., through the use of ultimate static bearing capacity calculations), it was to be expected that it was impossible to drive to the required penetration of 46 m with the hammers available.

The author's research group was nevertheless optimistic about the possibility to reach design penetration. Their prediction was that it should be possible to reach design penetration with the second-largest hammer available, the Menck 8000. This proved to be correct. Although the blow count was considerably higher than expected over most of the piles' penetration depth, the expected blow count range near design penetration was correct. (fig. 1; discussion in section 7).
Thermal Decay Time Logging At Ekofisk, Case Study Of A Multiple Use Tool
Authors: Golder George David
Published: December 2007

Thermal decay time (TDT) logging has proven to be a multiple use tool in the thick carbonate reservoirs at Ekofisk and nearby fields. Phillips Petroleum Company Norway has initiated a program to take a baseline log in each development well shortly after it has been put on production, to be followed by periodic future logs.

The original reason for obtaining a baseline log was to determine the TDT response at initial conditions in each well for comparison against future TDT logs, i.e., the usual 'time-lapse' technique, to monitor changes in water, gas and oil saturations at various stages of depletion. The Danian and Maestrichtian limestone reservoirs are commonly acid-fractured during completion in wells in the Ekofisk Area fields, so the baseline TDT log was also intended to determine how much correction for the 'acid effect' would have to be applied in each well.

The baseline TDT logs by themselves, however, are proving to be useful tools in applications other than those originally planned. The effect of acid on TDT log response has allowed the logs to be used to evaluate the effectiveness of acidizing and diverting techniques. Restimulations have been recommended and evaluated using TDT logs in conjunction with cased hole production logs. The usefulness of the TDT log in tracking the horizontal and vertical distribution of injection gas is also being evaluated.

Phillips believes that thermal decay time logging will be a basic, multiple use reservoir monitoring tool throughout the life of the Ekofisk Area fields.

INTRODUCTION

Soon after Phillips Petroleum Company Norway began development drilling in the Ekofisk Area fields (Ekofisk plus 5 other major carbonate reservoir fields and one small sandstone reservoir field) the need was recognized to gather data about initial conditions in each well to provide the basis for future reservoir monitoring efforts. A program was established, therefore, to obtain, in addition to normal openhole logs and completion tests, cased hole production logs and a baseline thermal neutron decay time (TDT*) log soon after the start of production in each well. Initially it was believed that the baseline TDT logs would be of limited use until comparisons could be made with future TDT logs, in the usual time lapse technique, to observe fluid saturation changes in the reservoir. In practice, however, the baseline TDT logs have proven useful in several unexpected ways.

THE TDT LOG

Since the development and introduction in the late 1960's of pulsed neutron logs to measure thermal decay times, TDT logs and, even more importantly, the techniques for their use and interpretation have matured greatly. TDT logging is now one of the most useful reservoir monitoring tools available to the industry.

When first introduced by Dresser Atlas as the 'Neutron Lifetime Log', and later by Schlumberger as the 'Thermal Neutron Decay Time Log', TDT logs were basically used for locating undepleted oil and gas zones behind casing in older fields or determining the source of high water cut production.
Importance Of Large-Scale LNG Operations To International Energy Supply
Authors: Coppack C.P.
Published: December 2007

Introduction

This is to be a talk about the liquified natural gas business, its potentialities and possibilities. It is a new business and one which can hardly be said to have started yet, as the first regular commercial cargo of liquefied natural gas has not yet been shipped. Nevertheless and in spite of this, I think that it is already reasonable to say that it is a business which will develop very considerably, in all probability on a worldwide scale. I do not think it would be going too far to describe its present stages as the birth of a whole new industry.

The first full scale commercial LNG venture will start operations this summer moving natural gas from Algeria to England. The liquefaction plant at Arzew near Oran will have a capacity of about 150/MM/CFD; two thirds of this capacity is for British Market and two ships are now nearing completion to carry this gas to the terminal installation in England which is being constructed by the Gas Council of Great Britain. About one third of the output of the liquefaction plant is destined for the French gas market and the French are now building a third LNG ship to carry this. I do not propose to describe this project and its history in detail.
The Development Decision For Frontier Areas: The North Sea
Authors: Warren Joseph E.
Published: December 2007

Despite the restrictions imposed by the hierarchial organization of most oil companies, including national companies, the exploration process does not logically end with a discovery. At least in high-risk, frontier areas, the contribution of exploration should continue until the development decision is made. This decision is the most economically significant one that must be faced during the course of establishing new productive capacity — the real goal of exploration.

Most frontier areas — deep, stormy waters far offshore or remote arctic regions — require massive capital investments for development; therefore, the development decision must be made in a timely manner even though available estimates of reserves and costs may be very uncertain. If the uncertainty involved is quantified, it is possible to specify a procedure that will yield optimal design parameters for any assumed level of reserves — optimality, in this sense, may be predicated on any chosen economic criterion. Then, taking into account the uncertainty in the estimated reserves, per se, an expected value for the chosen economic criterion can be determined for each assumed level of reserves. Finally, on the basis of these expected values, the optimal reserve value, for design purposes, can be found; and, the development decision may purposes, can be found; and, the development decision may be made by considering the distribution of the chosen economic criterion associated with the optimal design level of reserves.

A procedure for the determination of the optimal level of reserves, a discussion of the economic criteria that may be used, and an analysis of the development decision are presented in this paper. A simple numerical example is presented in this paper. A simple numerical example is also included.
Offshore Trials Of A Prototype Subsea Head Chamber
Authors: Hingston D.L.
Published: December 2007

Hingston, D.L., Vickers-Interek Ltd. UK.

Introduction

Vickers-Intertek Limited was formed in May 1976 in order to promote the demonstration and marketing of applications of the Neutrabaric method of working underwater in a one-atmosphere water-filled environment. Intertek are the inventors of the Neutrabaric system, which has now been patented in several other countries and Vickers were one of the first companies to develop the use of manned submersibles with lock-out capability. In January 1977, Vickers-Intertek launched a multisponsor project to design and build a prototype subsea wellhead chamber which would demonstrate an important application of the Neutrabaric system. The sponsors included American, Norwegian and British Oil Companies who made a significant contribution to the project through a Technical Advisory Committee which supervised the design, construction and trials ensuring that the prototype was designed to incorporate the latest developments in subsea technology and tested to meet all current and future oilfield requirements. Trials of the prototype were successfully completed in September 1978. The unit was installed first in 80 ft and then in 400 ft of water at a site near Kyle-of-Lochalsh off the West Coast of Scotland and was hydrostatically tested to 700 ft for Lloyds Certification. A diverless installation was demonstrated using hydraulic handling tools operated remotely from the surface. The unit was accessed on several occasions at each depth by men working at one atmosphere pressure from a manned submersible. A number of typical installation and maintenance tasks(and some unscheduled tasks) were demonstrated and the unit was recovered to the surface using the same diverless handling techniques.

DESIGN PHILOSOPHY

The fundamental philosophy behind the system is that standard oilfield equipment and standard techniques are used such as would apply to a wet-exposed tree subsea completion.
Drilling And Completion Of Buchan Field
Authors: Pinchbeck R.H. , Powell S.E.
Published: December 2007

The economics of oil and gas production in the North Sea are now leading the industry towards increasing use of subsea technology for the development of the smaller fields. The Buchan field, located some 150 kms NE of Aberdeen in 120 m of water, and with estimated recoverable reserves of the order of 50 million barrels, typifies the North Sea "marginal field". This paper describes the drilling and completion phases of Buchan development, and is presented as a companion paper to Geological aspects of the drilling Buchan field. The paper highlights the methods by which the potential hazards of drilling the highly-overpressured reservoir were overcome, outlines the evolution and implementation of the well completion methods adopted, and discusses problems encountered and lessons learned.

PROJECT OVERVIEW PROJECT OVERVIEW

The production system

Owing to the uncertainty about the performance of the tight and fractured reservoir and the low figure of recoverable reserves Buchan is a truly marginal field. The projection is that it will produce 50 million barrels over a period 5 years but the range of possible recoveries is wide and financial in the venture high. In the light of this risk any development scheme had to incur minimum expenditure and provide production at the earliest possible date. The scheme adopted, subsea completions with a floating production platform and tanker export, meets these criteria. Figure 1 shows the production system: oil is produced from seven subsea wells, (a central cluster of five at a template and two satellite wells) through a subsea manifold at the template and individual risers, to a semisubmersible production vessel. Degassed crude is then pumpted down the production vessel. Degassed crude is then pumpted down the manifold again through the 12 in. riser and out along the seabed for export via a CALM loading buoy.
Experiences With Surface Controlled Subsurface Safety Valves (SCSSV)
Authors: Agnew I.
Published: December 2007

Agnew, I. Shell UK Exploration and Production UK

Introduction

The surface controlled subsurface valve (SCSV) is the final means of maintaining control of a well when all surface controls no longer function. Although it is seldom necessary to call upon the full services of this value it is essential that it does respond with 100 percent reliability whenever the need arises. When a completion is being designed particular attention should be placed on the selection of the SCSSV to ensure that the best choice of valve is made to suit the well conditions.

This report outlines the reasons behind the selection for the hydrostatically balanced SCSSV used by Shell Expro for their Northern Sea operations with particular reference to the Brent field. The main problem encountered with this valve was the very poor reliability due to elastomer seal failures. Initially the external chevron "Vee" packing came under close scrutiny and a wide range of materials were tested and tried with very little success. Internal "O" ring seals were also investigated and it was found that the combination of elastometer hardness, diameter clearance between sealing surfaces, surface finish and pressure differential across the "O" ring was critical to enable the seal to perform satisfactorily "T" seals the reliability of the valve is beginning to improve. The practicality of balanced type of SCSSV's is not very promising. Problems have occurred with live balance lines, promising. Problems have occurred with live balance lines, gased up balance lines and increased failure probability due to the extra seals which have to be used. The balanced type ball valve does have the added advantage of being able to cut piano wire, but this does not compensate for its poor reliability. piano wire, but this does not compensate for its poor reliability. Valve setting problems have been encountered but it is anticipated that they could be overcome by improving the techniques being adopted.
The Installation Of An Eight Point Permanent Mooring System In The Piper Field
Authors: Lowe E.A.
Published: December 2007

The installation of an eight point permanent mooring system in the Piper permanent mooring system in the Piper field

The need for support vessels alongside North Sea platforms during offshore construction programmes has platforms during offshore construction programmes has focused attention on the problems of mooring and maintaining station in this service. In the past mooring systems subject to storm situations have been primarily designed for open ocean applications and primarily designed for open ocean applications and have not catered for the requirements of operating and surviving alongside a fixed platform. In addition, anchor handling and dragging of anchors had been seen to be the primary causes of damage to submarine pipelines.

The Piper field, located in the 58 degrees north sector of the North Sea, experienced these mooring difficulties compounded by poor top soil conditions, which led to the design and installation of a fixed permanent anchor pile mooring system around the platform. permanent anchor pile mooring system around the platform.

System Description

Eight anchor piles 60 in. diameter × 2 1/2 in. wall thickness × 94 ft long were driven with an HBM 1500 underwater hammer in a symmetric pattern around Piper 'A' providing suitable anchorage for construction vessels with operating draft displacements in excess of 40,000 L.T. Each pile was positioned 4,000 ft from the platform and has 1,010 ft of 3 1/2 and 4 in. chain attached for mooring. The free end of each chain is retrievable by pendant wire and buoy during connect/disconnect pendant wire and buoy during connect/disconnect operations.

Installation vessel choice

Pile and hammer handling capabilities Pile and hammer handling capabilities Early in the design stage, the use of stabilized lowering device such as the drill string of a drilling vessel was recognised as the optimum method of handling the hammer/follower/pile assembly. Pile/hammer stability calculations indicated the need for a sophisticated stabbing template to be pre-installed on the sea bottom if conventional unstabilized lowering devices were used. Since the template method would add considerable time and cost to the installation programme, our vessel search concentrated mobile drilling rigs.
Is There Enough Oil?
Authors: McAfee Jerry
Published: December 2007

Various recent energy studies and estimates of ultimate petroleum reserves, especially in the United States, make a realistic evaluation of the future petroleum supply and demand situation on a world-wide basis both pertinent and timely.

Adequate energy supplies are obviously of critical importance in maintaining, to say nothing of increasing, the world's living standards. Oil and natural gas now supply most of the U.S. energy requirements and a large part of the energy requirements of the entire Free World. The proportion supplied by petroleum in the Free World will probably continue to increase for at least another generation. A comparison with the U.S. is helpful in forecasting future Free Foreign requirements, in which natural gas will probably play an increasingly important role. Py 1975, U.S. consumption should be about 13 million B/D and Free Foreign consumption about 24 million B/D.

To supply these requirements and maintain a safe margin of reserves and producing capacity, about 200 billion barrels must be added to Free World proved reserves over the next 12 years. The ability of the U.S. to supply even 80% of its 1975 crude oil requirements from domestic sources at present prices is debatable, but other sources of oil are available and no world-wide shortage is likely. Free Foreign productive capacity and reserves will be more than adequate to supply Free Foreign requirements and to supplement U.S. domestic supplies as necessary, if the oil companies operating internationally are permitted a reasonable degree of freedom to discover new oil deposits and to match supplies against demands.
Numerical Simulations Of The Combined Effects Of Wellbore Damage And Partial Penetration
Authors: Saidikowski Ronald M.
Published: December 2007

There is considerable disagreement in the literature concerning the interpretation of wellbore damage (the skin effect) in partially completed wells. The skin factor is composed of two components, one of which is indicative of actual formation damage and the other of which results from an additional pressure drop due to the partial completion. The skin factor measured in a buildup test does not reflect the simple sum of these two components. Rather, the effect of the actual damage is accentuated by the partial completion. A method is presented to aid in the interpretation of well tests which yields estimates for both contributions to the skin factor.

Analysis techniques are derived for steady-state flow and these are corroborated for transient flow by using simulated well test results. The simulations also provide a basis for comparing the various correlations for determining the skin factor due to partial penetration. The importance of the ratio of vertical to horizontal permeability is considered in the analysis. An example illustrates the application of the method.

Introduction

An altered zone of reduced permeability surrounding a wellbore is quantified in terms of the skin factor, s. This factor is related to the excess steady-state pressure drop1,2 in a flowing well as:Equation 1

The flow efficiency, E, is expressed in terms of Î"ps and the total drawdownÎ"pw, as:Equation 2

The skin factor has been related3 to an altered zone near the wellbore (Figure 1). If a zone of reduced permeability, ka, extends a distance, ra, into the formation, then the skin factor, s, is:Equation 3

where rw is the wellbore radius and k is the bulk formation permeability.

It is the skin factor described by Equation 3 that is a measaure of the true formation damage caused by drilling and completion practices and other factors. This type of flow impediment is the target of acid treatment and other workover procedures. Thus, in order to evaluate completion practices and to recommend workover procedures, it is necessary to accurately determine the 'true' skin factor due to formation damage. In subsequent discussion this skin due to true damage will be designated as sd. The value of sd can be somewhat difficult to measure directly.

A well is often completed over only a portion of the producing formation (Figure 2). This leads to a flow construction which is detected as an additional pressure drop or skin effect. Several authors4,5,6,7,8 have developed analytical descriptions of the skin factor, sp, due to partial penetration in an otherwise undamaged reservoir. In particular, Nisle9 has developed a formulation for simulating well tests within an infinite acting reservoir with a partial completion. The concept of a skin factor is not introduced.