Lyons W.C. (ed.). Standard handbook of petroleum and natural gas engineering.2001- Volume 1
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Engineering Design
365
Because
the
last trial gives a close agreement with the
LHS
value of
208,189
cal, we
take the solution to be T,
A
1,345”C.
It is concluded that all of the three methods
of calculations provide the same final answer.
ENGINEERING DESIGN
Introduction
The Petroleum Engineer
Petroleum engineers
are
traditionally involved in activities known in the oil industry
as the “front end” of the petroleum fuel cycle (petroleum is either liquid or gaseous
hydrocarbons derived from natural deposits-reservoirs-in the earth). These front
end activities are namely exploration (locating and proving out the new geological
provinces with petroleum reservoirs that may be exploited in the future), and
development (the systematic drilling, well completion, and production of economically
producible reservoirs). Once the raw petroleum fluids (e.g., crude oil and natural
gas) have been produced from the earth, the ”back end of the fuel cycle takes the
produced raw petroleum fluids and refines these fluids into useful products.
Because
of
the complex interdisciplinary nature of the engineering activities of
exploration and development, the petroleum engineer must be conversant with
fundamentals of designing devices and systems particular to the petroleum industry
[67,68].
The petroleum engineer must be competent in skills related to engineering
design. Design involves planning, development, assembly and implementation of plans
to achieve a prescribed and specified result.
Multidisciplinary Team
The exploration activities directed at locating new petroleum-producing provinces
are cost-intensive operations. The capital expended in the search for new petroleum-
producing provinces is always at risk because there are no guarantee that such searches
will be economically successful. There is no way to actually “know” if crude oil or
natural gas is present in a particular geologic formation except to drill into the
formation and physically test it. Highly sophisticated geologic and geophysical methods
can be used to identify the possible subsurface geological conditions that might contain
crude oil and/or natural gas. However, the final test is to drill a well to the rock
formation (reservoir) in question and physically ascertain whether it contains
petroleum, and if it does, ascertain if the petroleum can be produced economically.
Thus, in the early part of the exploration phase geologists, geochemists, geophysicists
and petroleum engineers must form teams in order to carry out effective investigations
of possible petroleum producing prospects
[68].
In general, such teams are initially
driven by the geologic, geochemical and geophysical sciences that are to be used to
infer possible subsurface locations for new deposits
of
petroleum. However, once the
subsurface locations have been identified, the process of discovery becomes driven
by the necessity to drill and complete a test well
to
the prospective reservoir. The
skills of the exploration geologist are important for successful drilling. These
exploration (wildcat) wells are usually drilled in remote locations where little or no
previous subsurface engineering experience is available, thus, they are inherently
risky operations.
Development
of
new proven petroleum resources are also cost-intensive operations,
but generally lack the high risk of nearly total capital loss that exists in exploration
366
General Engineering and Science
activities. Development operations begin after the exploration test wells have proven
that crude oil and/or natural gas can be economically recovered from a new reservoir.
These operations require that numerous development
(or
production) wells be drilled
and completed into proven resources. Production equipment are placed in these wells
and the crude oil and/or natural gas is recovered and transported to refineries (in
the back of the fuel cycle). The placement of these wells and the selection of their
respective production rates within a particular reservoir or field must be planned
carefully. The pattern of well locations and production rates should be designed
so
that the largest fraction of the in-place petroleum can eventually be recovered even
though the maximum recoverable fraction of the oil
or
natural gas in place will not
reach
100
percent.
As
developmental wells are drilled and completed, the production
geologists ensure that wells are drilled to correct subsurface targets.
The development effort is largely a engineering activity requiring a great deal of
planning. This planning requires increased interaction of multiple engineering
disciplines to assure that the wells are drilled, completed and produced in a safe,
efficient and economical manner.
Engineering
Arts
and Sciences
There are three basic engineering fields of knowledge. These are called the
engineering arts and sciences. They are the mechanical arts and sciences, the chemical
arts and sciences, and the electrical arts and sciences. Every specific engineering
discipline, such as petroleum engineering, utilizes one of the basic engineering fields
of
knowledge as their scholarly foundation.
The mechanical arts and sciences are based on classical physics (or Newtonian
mechanics). The chemical arts and sciences are based on classical and modern
chemistry. The electrical arts and sciences are based on modern particle physics.
Table
247
gives a listing of the engineering disciplines that usually have the mechanical
arts and sciences as their foundation. Table
2-48
gives a listing of the engineering
disciplines that usually have the chemical arts and sciences as their foundation. And
Table
2-49
gives a listing of the engineering disciplines that usually have the electrical
arts and sciences as their foundation.
Note that a few disciplines such as petroleum engineering, environmental
engineering and nuclear engineering are listed under two of these general engineering
fields. At one engineering university, for example, the petroleum engineering
curriculum
may
have a mechanical arts and sciences foundation. At another university,
the petroleum engineering curriculum could have a chemical arts and sciences
foundation. However, most petroleum engineering curricula are based on the
Table
2-47
Mechanical
Arts
and Sciences Engineering Disciplines
Mechanical Engineering
Civil Engineering
Aeronautical and Aerospace Engineering
Materials and Metallurgical Engineering
Mining Engineering
Petroleum Engineering
Marine Engineering
Ocean Engineering
Environmental Engineering
Engineering Mechanics
Engineering Science
Industrial Engineering
Nuclear Engineering
Fire Protection Engineering
Engineering Physics
Engineering Design
367
Table
2-48
Chemical Arts and Sciences
Engineering Disciplines
Chemical Engineering
Petroleum Engineering
Environmental Engineering
Nuclear Engineering
Table
2-49
Electrical Arts and Sciences
Engineering Disciplines
Electrical Engineering
Electronics Engineering
Engineering Physics
mechanical arts and sciences. Petroleum engineering curricula that are based on the
mechanical arts and sciences usually have a balanced emphasis regarding drilling
and completions, production
and
reservoir engineering subjects. Curricula that are
based on the chemical arts and sciences generally concentrate on reservoir engineer-
ing subjects.
Similar situations occur with curricula in environmental engineering and in
nuclear engineering.
Scientific and Engineering Philosophies
Scientific Method
The foundation philosophies of science and engineering are quite different. In the
historical sense,
it
is obvious that scientific inquiry came first. In order for humans to
“engineer,” they had to be able to predict certain potentially useful physical
phenomena. Thus, the scientific method evolved to aid humans in systematically
discovering and understanding natural phenomena. The scientific method is a set
of
prescribed steps that are used to assist in understanding hitherto unknown natural
phenomena. Table
2-50
gives a listing of the basic steps of the scientific method. The
scientific method is an iterative procedure and in modern settings requires the
development of a carefully devised plan of work. Such a plan requires both
experimentation and analysis. It is necessary for the scientist to keep careful records
in order to assure that little will be missed and that other investigators will be able
to
carry
out
any follow-on work. It
is
important to understand that the act of seeking
pure knowledge is mutually exclusive of any desire to apply the gained knowledge to
anything useful. In essence, the scientist seeks a unique and comprehensive
understanding (or solution) of phenomena.
Engineering Method
The scientific method has been successfully used throughout human history to
enlighten us to our natural world and beyond. Since the earliest days there have been
368
General Engineering and Science
Table
2-50
Scientific
Method
~
Observe a phenomenon
Postulate a theory to explain the phenomenon
Develop and conduct an experiment to test the validity
of
the theory
Using the test results, draw conclusions as to the validity
of
the theory
Re-postulate the theory in light of these conclusions
Iterate the above steps and continue to refine theory
individuals who desired to use scientific knowledge for practical use within their
respective societies. The modern engineer would have little trouble recognizing these
individuals as our forerunners.
Modern engineering has its formal roots in France where, in
1675,
Louis XIV
established a school for a corps of military engineers. Shortly afterward, early in the
reign of Louis
XV,
a
similar school was created for civilian engineers
[69].
These
original engineering schools were created to provide trained individuals who could
improve the well-being of French society by creating an economical infrastructure of
water, sewer and transportation systems.
By
the time modern engineering was
established in the United States, the idea of the dependence of engineering practice
on scientific knowledge was well established. This is illustrated by the original charter
of the Institution of Civil Engineers in
1828
(the first professional engineering society
in the United States, know known as the American Society of Civil Engineers) by the
following statement
.
.
.
“.
.
.
.the art
of
directing the great sources of power in Nature for the use and
convenience of man.
. .
.”
In recent years there has been a greater appreciation of the word “use.”
As
society
and engineers have become more aware of the systems or process aspects
of
nature,
it has become clear that the use of natural resources must stop short of abuse.
In early engineering practice, products (devices or systems) evolved slowly with
step-by-step improvements made after studying the results of actual usage. In those
early days, engineeringjudgments were made by intuition (Le., parts are strong enough,
etc.), and engineering design was the same
as
engineering drawing.
As
society’s needs
for new products expanded and as each product become more complicated, it also
became necessary to develop an engineering methodology that would assure economic
and systematic development of products. In time, the engineering community
developed the engineering method. Table
2-51
lists the basic steps of the engineer-
ing method.
The unique characteristics of the engineering method are:
1.
the engineering method is initiated by the desire to create a product that will
2.
the created product will be economically affordable and “safe” for use by society.
However, like the scientific method, the engineering method is an interative process
and embedded in the engineering method is the systematic use of the scientific method
itself to predict behavior of a prototype device
or
process. This means both methods
require the use of trial and error. The interdependency of trail and error
was
explained
by someone who said.” One cannot have trail and error without error.”
meet the needs
of
society, and
Engineering Design
369
Table
2-51
Engineering Method
A
problem is recognized or a need is identified.
Establish performance specifications (based on the details of the need stated above)
Describe the preliminary characteristics of the life-cycle that the product design” should have
Create first prototype design
Evaluate feasibility of first prototype design from both the technical and economic point-of-view
Evaluate performance characteristics of first prototype using models (usually both analytic and
Fabricate first prototype
Test first prototype
Iterate the above process until society is satisfied and accepts the product
Plan for the maintenance and retirement of the product through its life-cycle
(i.e., relative
to
production, distribution, consumption and retirement)
and modify first prototype design appropriately
physical) and using the results, modify first prototype design appropriately
~~
“The product in petroleum engineering may be as large and as inclusive as an entire oil field or
it may be as small as a component
of
a machine or a process used
in
production.
Since the desire of society* to improve its condition will likely always exceed its
complete scientific and economic knowledge to do
so,
the engineer must learn to
deal with ambiguity-physical as well as societal. Ambiguities in engineering
will
always result in several useful engineering solutions (or alternative solutions) that
can meet a perceived need. Thus, the engineering method, by its very nature, will
yield alternative solutions. Society is then required to select one or more of those
solutions to meet its need. However, society may decline all of the alternative solutions
if
the long term results of applying these solutions are unknown or
if
they have known
detrimental outcomes. This
was
the situation in the United States and in other
countries regarding the commercial application of nuclear energy.
The
‘‘Art‘‘
of
Engineering Design
Engineering design is a creative act in much the same way that the creation of fine
art is a creative act. This is why the three general fields of knowledge are described as
“arts and sciences.” This description acknowledges that engineering activity is a
combination of creative “art” and knowledge in science. The act of design is directed
at the creation of a product (for society’s use) which can be, in broad terms, either a
device or a system.
Probably the most difficult part of engineering design
is
the “definition of the
problem.” This part of engineering design is described by the first three steps of
Table
51
(Le., the engineering method). To define
a
problem for which the engineer
may design several alternatives solutions requires extensive study of society’s need
and the analysis of applicable technologies that may be brought to bear. The most
important aspect of engineering design is the assessment of whether society will
accept or reject the engineer’s proposed designs. Modern engineering practice is
‘“Society” is used in a generic sense here. Depending on context, society may mean society at large.
It
may
mean a
local community. corporation, operating division
of
a company
or
corporation,
or
it
may mean the
immediate association
of
employees
or
personnel.
370
General Engineering and Science
littered with engineered “solutions” to the wrong problem. Such situations emphasize
the need for engineers to assure the correct problem is being solved.
Device Design
A device is a product having all major parts are essentially made by a single
manufacture. Thus, the device design and its manufacturing operation are under the
complete control
of
the designer. This definition does not dictate a particular product
size or complexity, but does infer that such a product will have limited size and
complexity.
The creation of these device designs is somewhat abstract with regards to providing
products for the “needs of society.” The device designs are in support of an industry
which
is
vital to society’s operation. Thus, the designer
of
a device for the petroleum
industry designs, in a sense, for society’s needs. In the petroleum industry, suppliers
of
hardware and services for operating companies function more in the area of
designing devices than in the design and supply of systems (or processes) that produce
natural petroleum resources.
System Design
A system design is a product that is made up of a combination of devices and
components. As described above the devices within a system are under the control of
the designer and are designed specifically for the system. Components, on the other
hand, are other devices and/or subsystems which are not made to the specification
of
the system designer. Usually these components are manufactured for a number
of
applications in various systems. Thus, the system design and the fabrication of the
system are under the control of the system designer. The definition of a system infer
complexity in design and operation.
In the petroleum industry, the term system and process are often considered
synonymous. This is basically because engineering designers in the industry create
“systems” that will carry out needed operational “processes” (e.g., waterflood project).
Role
of
Models
Once the problem has been defined and the decision has been made to proceed
with a design effort (device or system), the conceptual designs and/or parts of the
device or system are modeled, both mathematically and physically. Engineers design
by creating models that they can visualize, think about, and rearrange until they
believe they have an adequate design concept for practical application. Therefore,
modeling is fundamental to successful engineering design efforts and is used to predict
the operating characteristics of a particular design concept in many operational
situations.
Mathematical
Models.
In modern engineering practice it is usually possible to develop
mathematical models that will allow engineers to understand the operational
characteristics of a design concept without actually fabricating or testing
the
device
or system itself. Thus, analysis (using mathematical models) usually allows for great
economic savings during the development of a device or system. To carry out such
analyses, it is necessary to separate a particular design concept into parts-each
of
which being tractable to mathematical modeling. Each of these parts can be analyzed
to obtain needed data regarding the operating characteristics of a design concept.
Although repetitive analyses of models are exceedingly powerful design tools, there
Engineering Design
371
is always the risk that some important physical aspect of a design will be overlooked
by the designer. This could be a hitherto unknown phenomenon, or an ignored
phenomenon, or simply an interaction of physical phenomenon that the separate
analysis models can not adequately treat.
Physical
Models.
At some point in the design process it is usually necessary to
create physical models. Often these physical models
are
of separate parts of the design
concept that have defied adequate mathematical modeling. But most often physical
models are created to assist in understanding groups or parts of a design concept
that are known to have important interactions.
As
in mathematical modeling, physical
modeling usually requires that the design concept be separated into parts that are
easily modeled. Physical modeling (like mathematical modeling) allows the engineer
to
carry out economic small scale experiments that give insight into the operational
characteristics of the design concept. Physical modeling must be carried out in
accordance to certain established rules. These rules are based on principals given in
the technique known as dimensional analysis (also known as Lord Rayleigh’s method)
or
in a related technique known as the Buckingham
ll
theorem [70,71,72].
DimensionalAnalysis.
In the design of rather simple devices or systems, dimensional
analysis can be used in conjunction with physical model experimental investigations
to gain insight into the performance of a particular design concept. It is usually possible
to define the performance of a simple device or system with a certain number
of
well
chosen geometric and performance related variables that describe the device or system.
Once these variables have been selected, dimensional analysis can be used to:
1.
Reduce the number of variables by combining the variables into a few
dimensionless terms. These dimensionless terms can be used to assist in the
design of a physical model that, in turn, can be used for experimentation (on
an economic scale) that will yield insight into the prototype device or system.
2. Develop descriptive governing relationships (in equation and/or graphical form)
utilizing the dimensionless terms (with the variables) and the model experimental
results that describe the performance of the physical model.
3.
Develop device or system designs utilizing the descriptive governing relationships
between the dimensionless terms (and subsequently between the variables) that
are similar to those of the tested physical model, but
are
the dimensional scale
of the desired device or system.
Dimensional analysis techniques are especially useful for manufacturers that make
families
of
products that vary in size and performance specifications. Often it is not
economic to make full-scale prototypes of a final product (e.g., dams, bridges,
communication antennas, etc.). Thus, the solution to many of these design problems
is
to create small scale physical models that can be tested in similar operational
environments. The dimensional analysis terms combined with results
of
physical
modeling form the basis for interpreting data and development of full-scale prototype
devices
or
systems. Use of dimensional anaiysis in fluid mechanics
is
given
in
the
following example.
Example
1
To
describe laminar flow of a fluid, the unit shear stress
T
is some function of the
dynamic viscosity p(lb/ft*), and the velocity difference dV(ft/sec) between adjacent
laminae that are separated by the distance dy(ft). Develop a relationship for
T
in
terms of the variables
p,
dV and dy.
372
General Engineering and Science
The functional relationship between
z
and m, dV and dy can be written as
z
=
K(ya
dvb dy’)
Using Table
2-52
the dimensional form of the above
is
(FL-2)
=
K
(FL-2T)” (LT-’)b
(L)’
Table
2-52
Dimensions and Units
of
Common Variables
Dimensions Units
Symbol Variable
M
LT
FLT USCW
SI
Geometric
L
Length
L
ft
m
A
Area
L2
ft2 m2
V
Volume
L3
ft3
m3
Kinematic
7
Time
T
S
S
W
Angular velocity
f
Frequency
V
Velocity
LT-‘
fWs mls
T-’
S-’
S-‘
V
Kinematic viscosity LTT-’ ft2ls
m2/s
Q
Volume flow rate
L3T-’ ftVs
m3/s
a
Angular acceleration T-2
5-2
5-2
a
Acceleration
LT-2 fWs-2
m/s2
Dymanic
P
Density
ML-1 FL’P
slug/ft3 kg/m3
M
Mass
M FL-’P
slugs kg
I
Moment of inertia
ML2
FLP
slug.ft2
kgm2
CI
Dynamic viscosity
ML-‘ T-’
FL-2
T
slugIfWs kglmls
M
Mass flow rate
MT-’
FL-’ T-’
sluals
kals
MV
Ft
Momentum
Impulse
MLT-‘ FT
Ibf-s
Nos
Mw
Angualar momentum
ML2T-’ FLT
slug-ft21s kg*m2/s
Y
Specific weight
ML-2
T-2
FL-3
Ibf/ft3
N/m3
Engineering Design
373
Table
2-52
(continued)
P
E
T
Pressure
Unit shear stress
ML-'
T-2
lbfW Nlm2
Modulus of elasticity
0
Surface
tension
MT-Z
FL-'
Ibflft
N/m
F
Force
IVLT-~
F
I
bf
N
E
Energy
W
Work
ML2F2
FL
Ibf/ft
J
FL
Torque
P
Power
ML2T4
FLT-'
lbf*ft/s
w
u
Specific volume
t~t'L4T-~
ft3/lbm m3/kg
+
United States customary units
The equations for determining the dimensional exponents a,
b
and c are
Force
F
1
=
a
+
0
+
0
Length
L:
-2
=
-2a
+
b
+
c
TimeT O=a-b+c
Solving the above equations for a, b and c yields
a=
1
b=l
c=-1
Thus, inserting the exponent values gives
z
=
K(y1
dV1 dy-I)
which can be written as
t
=
K[P
(dV/dy)l
where
the constant
K
can be determined experimentally for the particular design
application.
Buckingham
l7.
The Buckingham
Il
theorem is somewhat more sophisticated than
the dimensional analysis technique. Although directly related to the dimensional
analysis technique, Buckingham
Il
is usually used in design situations where there
is
less understanding of exactly which performance characteristics are ultimately
important
for
prototype design. Also, the Buckingham
Il
theorem is generally more
applicable to the design of complex devices
or
systems. In particular, Buckingham
Il
374
General Engineering and Science
is usually used when the number of dimensionless terms needed to describe a device
or
system exceeds four. The fundamental theorem is
. . .
“if an equation is dimensionally homogeneous (and contains all the essential
geometry and performance variables) it can be reduced
to
a relationship among
a
complete set
of
dimensionless terms of the variables.”
Applications of the Buckingham
lT
theorem results in the formulation
of
dimensionless
terms called
ll
ratios. These
ll
ratios have no relation to the number
3.1416.
Example
2
Consider the rather complicated phenomenon
of
the helical buckling of drill pipe
or production tubing inside
a
casing. This is a highly complicated situation that must
be considered in many petroleum engineering drilling and production operations.
In general, this involves the torsional post-budding behavior of a thin walled elastic
pipe. The mathematical model for this situation is very complicated and dependable
closed-form solutions of this problem do not exist. But still the designer must obtain
some insight into this phenomena before an engineering design can be completed.
The problem can be approached by utilizing the principals of physical modeling
based on the Buckingham
ll
theorem. What is sought is a set of dimensional
relationships (the
l7
ratios) that are made up of the important variables
of
the problem.
These
n
ratios may then be used to created
a
small-scale experiment that will yield
data that can be used to assist in the design the prototype (or full-scale pipe system).
The important variables in this problem are E1 (lb-in2
or
lb-ft2) the flexural rigidity of
the thin-walled elastic pipe (which is directly related to the torsional rigidity
GJ
through
known material constants), the length
of
the pipe L(ft), the shortening of the pipe
8(ft) (as it helically twists in the casing), the annular distance between the outside of
the pipe and the inside of the casing (d2
-
d,)(ft) (where d, is the outside diameter of
the pipe and
4
is the inside diameter of the casing), the applied torque to the pipe
T(ft-lbs), and the applied tension in the pipe P(1bs).
Using Table
52
the variables are El(FL2), L(L), d(L), (d2
-
d,)(L),
T(FL),
and
P(F).
Note that this I is moment-area which is in the units of
ft4
(not to be confused with I
given in Table
52
which is moment
of
inertia, see Chapter
2,
Strength
of
Materials,
for clarification). The number of
n
ratios that will describe the problem is equal to
the number
of
variables
(6)
minus the number of fundamental dimensions
(F
and L,
or
2).
Thus, there will be four
rI
ratios (Le.,
6
-
2
=
4),
n,,
112,
n,,
and
n4.
The
selection of the combination of variables to be included in each n ratio must be
carefully done in order not to create a complicated system of ratios. This is done by
recognizing which variables will have the fundamental dimensions needed to cancel
with the fundamental dimensions in the other included variables to have a truly
dimensionless ratio. With this in mind,
ll,
is
ll1
=
Ela Tb Lc
and
lT2
is
112
=
Td
P’
Lf
and
ll,
is
Ils
Lg
(d2
-
d,)h