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Stress analysis of drillstring threaded connectionsSalihu, B. M. January 2011 (has links)
The demand for energy from developed and developing economies of the world is driving the search for energy resources to more challenging environments. The exploration and exploitation of hydrocarbons now requires the drillbit to hit pay zones from drillships or platforms that are located on water surfaces below which is, possibly, in excess of ten thousand feet of water above the sea bed. From Brazil, to the Gulf of Mexico and the Gulf of Guinea on the western coast of Africa, hitherto unfamiliar, but now common, concepts in the drilling parlance such as ultra-deep drilling (UDD), ultraextended- reach drilling (uERD) and slimhole drilling, are employed to reach and produce reservoirs which a few decades ago would seem technologically impossible to produce. This is expected to exert tremendous demands on the physical and mechanical properties of the drillstring components. Limiting factors for reaching and producing oil and gas resources hidden very deep in the subsurface are both the capacity of the drilling rig to support the weight of the drillstring, which in some instances can be several kilometres long, and the bending, tensile and impact stresses the string has to withstand in well trajectories that are getting both longer and more tortuous. Associated with this increased well depths and complex well trajectories is the prohibitive cost penalty of a failed drillstring. The in-service failure of drillstrings has always been an issue in the industry long before the wells become this deep and complex. The global oil and gas industry estimates the cost of string failure to be in excess of quarter of a billion dollars annually. Researchers are continuously looking for ways to design against string failure and improve the level of confidence in drillstrings. Defect-tolerant design, tooljoint geometry modification and surface coldworking are just a few of the ideas that have gained mileage in this effort. Others that are now in consideration are the use of nonconventional materials such as aluminium and titanium alloys for drillstring components. More novel, still, is the use of a combination of two materials - one ‘softer’ than the other to form a hybrid string of two materials of unequal moduli of elasticity. This is done to make the string lighter, reduce stress concentration factor at the connections and place fatigue resistant materials in areas of high well bore curvature.In this work a computational technique in the form of two-dimensional finite element analysis is used to develop a robust model of a drillstring connection and to analyse the stresses on the model of a threaded connection of standard drillstring tooljoint made from alloy steel. Further comparative analyses were undertaken on models of drillstrings made from a newly developed drillstring material for ultra-deep drilling, the UD-165, aluminium and titanium alloys and, finally, on hybrid drillstrings made from two different materials of unequal moduli of elasticity. The aim is not only to develop and validate a better method of computational drillstring analysis but also to use the model to investigate and suggest areas of optimisation that will benefit industry especially in the areas hybrid strings.
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Stress analysis of drillstring threaded connectionsSalihu, B. M. 11 1900 (has links)
The demand for energy from developed and developing economies of the world is
driving the search for energy resources to more challenging environments. The
exploration and exploitation of hydrocarbons now requires the drillbit to hit pay zones
from drillships or platforms that are located on water surfaces below which is, possibly,
in excess of ten thousand feet of water above the sea bed. From Brazil, to the Gulf of
Mexico and the Gulf of Guinea on the western coast of Africa, hitherto unfamiliar, but
now common, concepts in the drilling parlance such as ultra-deep drilling (UDD), ultraextended-
reach drilling (uERD) and slimhole drilling, are employed to reach and
produce reservoirs which a few decades ago would seem technologically impossible to
produce.
This is expected to exert tremendous demands on the physical and mechanical
properties of the drillstring components. Limiting factors for reaching and producing oil
and gas resources hidden very deep in the subsurface are both the capacity of the
drilling rig to support the weight of the drillstring, which in some instances can be
several kilometres long, and the bending, tensile and impact stresses the string has to
withstand in well trajectories that are getting both longer and more tortuous.
Associated with this increased well depths and complex well trajectories is the
prohibitive cost penalty of a failed drillstring. The in-service failure of drillstrings has
always been an issue in the industry long before the wells become this deep and
complex. The global oil and gas industry estimates the cost of string failure to be in
excess of quarter of a billion dollars annually.
Researchers are continuously looking for ways to design against string failure and
improve the level of confidence in drillstrings. Defect-tolerant design, tooljoint geometry
modification and surface coldworking are just a few of the ideas that have gained
mileage in this effort. Others that are now in consideration are the use of nonconventional
materials such as aluminium and titanium alloys for drillstring
components. More novel, still, is the use of a combination of two materials - one ‘softer’
than the other to form a hybrid string of two materials of unequal moduli of elasticity.
This is done to make the string lighter, reduce stress concentration factor at the
connections and place fatigue resistant materials in areas of high well bore curvature.In this work a computational technique in the form of two-dimensional finite element
analysis is used to develop a robust model of a drillstring connection and to analyse the
stresses on the model of a threaded connection of standard drillstring tooljoint made
from alloy steel. Further comparative analyses were undertaken on models of
drillstrings made from a newly developed drillstring material for ultra-deep drilling, the
UD-165, aluminium and titanium alloys and, finally, on hybrid drillstrings made from two
different materials of unequal moduli of elasticity.
The aim is not only to develop and validate a better method of computational drillstring
analysis but also to use the model to investigate and suggest areas of optimisation that
will benefit industry especially in the areas hybrid strings.
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[en] DEVELOPMENT OF A VIBROIMPACT DEVICE / [pt] DESENVOLVIMENTO DE UM DISPOSITIVO GERADOR DE VIBROIMPACTOROMULO REIS AGUIAR 29 March 2006 (has links)
[pt] A perfuração de rochas duras ainda é um grande desafio
para as empresas de perfuração e exploração de petróleo.
Uma das linhas de pesquisas atuais consiste em combinar
satisfatoriamente duas técnicas de aumento da taxa de
penetração. Esta nova técnica vem sendo chamada de
perfuração percussiva-rotativa auto-excitada. Esta
dissertação se propõe a desenvolver o primeiro protótipo
de um dispositivo que irá operar em ressonância e que será
capaz de gerar forças dinâmicas expressivas. De forma
resumida, este dispositivo será chamado de RIMD (Resonant
Impact Device). Em princípio a idéia é construir um
dispositivo em forma de uma caixa preta, na qual será
montada na estrutura que vibra, tendo esta caixa dois
ajustes, um calibrando a freqüência de ressonância do RIMD
e outro agindo sobre os impactos (folga). É conhecido de
trabalhos anteriores que o tamanho da folga também possui
influência sobre a freqüência natural do sistema. Desta
forma, existe uma interdependência entre ambos os ajustes.
Um dos primeiros passos no projeto e desenvolvimento do
protótipo do RIMD é o dimensionamento do mesmo, de forma
que seja pequeno o suficiente para facilitar sua
construção e instrumentação no laboratório de vibrações da
PUC-Rio, bem como seja representativo do sistema em
tamanho real (a ser implantado na coluna de perfuração).
Os componentes do RIMD envolvem um sistema massa-mola com
baixo amortecimento e algum dispositivo de impacto e de
variação da folga. Após a concepção e construção do
protótipo, os passos seguintes do estudo são a obtenção
das características do RIMD, como a faixa de freqüências o
qual atua e a medição das forças impulsivas geradas. Por
último, o protótipo também servirá para validar um modelo
analítico que permitirá investigações posteriores neste
tema, podendo gerar outras possibilidades de construção do
RIMD. / [en] Hard rock drilling is still a great challenge for oil
companies.
One current line of research involves combining the two
existing drilling
techniques in order to enhance the rate of penetration.
This new technique
is called Resonance Hammer Drilling. This dissertation
proposes the
design and development of the first prototype that will
operate in resonance,
and will be capable of generating considerable dynamic
forces. This device
will be known as the Resonant Impact Device, or RIMD. In
principle
the idea is to build some sort of black box, which will be
mounted on a
vibrating structure with two switches - one calibrating
the RIMD resonance
frequency and the other acting on the impacts - changing
the size of the gap.
It is known from previous work that gap size also has
influence on the system
natural frequency. Therefore there is a relationship
between switches. One
of the first steps of RIMD design and development is
device dimensioning,
necessary in order to construct a scale model at the
Dynamic and Vibration
laboratory at PUC-Rio representative of the real size
system. The real size
system will be mounted on the drillstring. RIMD components
involve a
mass-spring system with low damping and some impact and
gap variation
devices. The analysis of this prototype includes obtaining
key characteristics
such as the range of possible frequencies and the
measurement of the
generated impulsive forces. Finally, the built prototype
will be used to
validate an analytical model that will allow further
investigations on this
subject providing the way to other possible constructions.
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