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Production Exam 2 (M)
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Terms in this set (178)
T/F: Nodal analysis must be performed with the node at the well bottomhole
False
If the number of perforations increase, how does nodal analysis change?
increases due to IPR increase
Mass Balance:
What is the equation for mass flow rate used?
m (dot) = density
area
velocity
Momentum Balance:
Acceleration term is negligible except at ___ pressures that are < ___ psia
low
100 psia
Momentum Balance:
Gravitational term in wells makes up
85-100%
Momentum Balance:
Frictional term in wells makes up
0-15%
Momentum Balance:
Gravitational term in pipelines makes up
0-30%
Momentum Balance:
Frictional term in pipelines makes up
70-100%
SI units of desnity
kg/(cu.m)
Field units for density
lb/cu.ft
Equation for:
Velocity (v) =
Flow Rate (q) =
v = q/A
q = v*A
Reynolds # in laminar flow
< 2100
Reynolds # in turbulent flow
> 2100
How does pipe roughness affect the pressure drop calculations?
Increasing roughness will increase the frictional pressure gradient
Compressible/Incompressible
Oil/water =
Gas =
* incompressible
* compressible
For compressible fluids such as gas, the gas expands causing the density to ___ and velocity to ___ changing mass balance
decrease
increase
For incompressible single phase flow, the ___, ___, and ___ changes can be neglected since they are constant
density, velocity, acceleration
What are the well calculations in the Marching Algorithm? (4)
1.) Calculations are started from known wellhead pressure and the well is divided into n (sections) elements
2.) Fluid properties are calculated at average pressure for every n or element assuming it is constant across the entire element
3.) An iterative method is required for the average pressure of each n or element since the outlet pressure is unknown
4.) The final output is the well bottom hole pressure
Surface pressure measurements:
With packer means
BHP is independent of casing pressure.
Surface pressure measurements:
With a packer, what must be done to calculate pressure losses?
Knowledge of fluid properties with pressure is required to know the changes of in-situ density, viscosity, and velocity from top to bottom in the wellbore
Surface pressure measurements:
Without packer means
BHP requires casing head pressure
Surface pressure measurements:
Without packer, how do you know the liquid density in the annulus?
In stabilized flowing wells, in order to know the average annulus density, the liquid level in the annulus must be known. Therefore, operations such as shooting the liquid (fluid) level is done using gas guns.
How is liquid level in a well determined
gas guns, shooting the fluid level
Conservation of energy:
What is U?
U is the overall heat transfer coefficient
Conservation of energy:
What does it predict in wells? (3)
1.) heat loss from surface to bottom hole in injection wells
2.) Fluid properties for pressure traverse predictions
3.) Deposits like wax, hydrate, asphaltene, and scale
Conservation of energy:
What does it predict in pipelines? (2)
1.) Fluid properties for pressure traverse predictions
2.) Deposits like wax, hydrate, asphaltene, and scales
High bottom hole pressure results in lower ___ that decreases ___
drawdown
production
Nodal Analysis:
Pres and Psep can be considered constant at a specified time due to what?
Pres is constant due to the pressure not changing from the formation at a specified time.
Psep is constant due to controlling the pressure of the separator using equipment
What is a node
any point of interest along the production system
what are the units of a node
dimensionless
Node locations vary throughout the ___ system from sales to separators to downhole
production
T/F: Nodes are ONLY placed at bottomhole
False
What is a component
any system element between two consecutive nodes
Mass flow rate into the node ___ the mass flow rate out of the node
equals
How many pressures exist at a node
One unique
A unique relationship between ___ and ___ drop must exist for each component in nodal analysis
flow rate and pressure
nodal analysis requires _____ pressures to be fixed at any time. These pressures are ___ and ___ or ___
two
Pr and Psep or Pwh
Node:
1.) Any point of ___ along the production system
2.) Node has no ___
3.) Typically, a node has unique ___, ___, and ___
4.) Common examples ___, ___, ___
1.) interest
2.) dimension
3.) pressure, temperature, and flow rate
4.) bottom hole, wellhead, separator
Nodal Analysis Principles:
At the node, ___ = ___
Left side =
Right side =
The two sides should result in the same ___
Pinflow = Poutflow
IPR
OPR
Pressure
Pinflow and Poutflow can be considered ___ for wellbore pressure calculations
Pwf
IPR/OPR
What is associated with inflow
IPR
IPR/OPR
What is associated with outflow
OPR
Nodal analysis results in both ___ and ___ curves to interpolate their relationships
IPR and OPR
IPR shows the pressure that the reservoir ___ at the wellbore
OPR shows the pressure ___ at the wellbore to produce at that rate
provides
required
Intersection of IPR and OPR is called
Operational Point
IPR at 0 Pwf is
AOFP
For OPR at a given flow rate, higher Pwf value of the OPR =
higher pressure losses at the wellbore and surface
Normally, if we only look at the OPR, at higher Pwf cases, a higher flow rate can be produced meaning we have higher ___ losses
frictional
OPR is also called ___ or ___
TPR (tubing performance relationship)
VFP (vertical flow performance)
Similar to IPR, OPR gives a relationship between ___ and ___ (considering bottom hole as the node)
flow rate and Pwf
Nodal Analysis (single phase):
1. IPR is ___
2. Tubing is filled with liquid, so the ___ pressure loss is constant
3. ___ pressure losses change as flow rate changes. It increases almost ___ with flow rate.
4. What is the most important change in pressure or deltaP?
1. linear
2. gravitational
3. Frictional, linearly
4. Tubing or deltaPtubing
Friction factor is a function of ___, so it will change based upon this rate of change.
flow rate
Generally, larger tubing and flowlines will result in less ___ and more ___. Although, the production is hard to maintain for long periods of ___
friction
production
time
Flow line and tubing diameters:
Larger = ___ operating pressure
Smaller = ___ operating pressure
lower
higher
Effects of flow line size are negligible at diameters > ___
Effects of tubing size are negligible at diameters > ___
3"
3.5"
Maximum achievable flow rate is for the case with no ___
friction
OPR (Two Phase):
1. Changes in the two phase flow pattern within the tubing affect the ___ pressure gradient due to the changes in liquid ___ and mixture ___
2. ___ pressure gradient is also affected due to changes in phase ___
gravitational
holdup
density
frictional
velocities
Two phase Nodal Analysis is more ___ than single phase
complex
Nodal Analysis (Two Phase):
IPR is not ___
linear
Nodal Analysis (Two Phase):
Gravitational pressure losses __________ at low production rates
increase
Nodal Analysis (Two Phase):
Frictional pressure losses __________ at lower production rates
decrease
Nodal Analysis (Two Phase):
From the minimum OPR, increase of Pwf to the left is due to fluid ___ while increase of Pwf to the right is due to increasing ___
hold-up
friction
Nodal Analysis: Completions (Two Phase)
Does skin effect OPR and IPR and what is the trend?
IPR, it affects the trend as skin increases from right to left (s = 0 on right)
Nodal Analysis: Perforations (Two Phase)
Increasing perforations will ___ IPR. Effect becomes small after perfs (N) = ___
increase (allows more flow)
10
Nodal Analysis: Perforation Density (Two Phase)
As perforation density increases, the flow rate ___. Effects become small after density =
increases
5-10 shot/ft
Nodal Analysis: Tubing Size Selection (Two Phase)
How does diameter affect OPR curves?
Smaller diameter results in larger operational point/higher pressure/lower flow rate. Larger diameter results in lower operational point/lower pressure/higher flow rate.
Nodal Analysis: Tubing Size Selection (Two Phase)
With diameter increase, initially friction ___, reducing total pressure drop in a friction dominated system causing OPR to shift ___. Then, ___ losses start increasing to eventually dominate the pressure losses and shift OPR back ___. Nodal analysis helps select the ___ tubing size.
decreases
down
gravitational
up
optimum
Nodal Analysis (Two Phase): Tubing Size Selection
Increasing diameter too much results in ___ flow rate that can actually hurt production
unstable
Nodal Analysis (Two Phase): Flow Line Selection
The node is placed at the ___, so IPR includes both ___ and ___
wellhead
reservoir and wellbore
Nodal Analysis (Two Phase): Flow Line Selection
As the diameter increases, ___ decreases and ___ shifts down
friction
OPR
Nodal Analysis (Two Phase): Flow Line Selection
Placing the node at the ___ can help find the optimum tubing and flow line sizes. Especially in ___ systems with large ___ losses in flowline
wellhead
offshore
pressure
Nodal Analysis: (Two Phase)
Larger tubing and flowline sizes become economically ___ if the increase in ___ is too small. This is due to larger pipe sizes being more ___
inefficient
production
expensive
In general, for tubing and flowline sizes, as diameter increases, ___ decreases and the OPR shifts ___
friction
down
Nodal Analysis (Two Phase):
Artificial lifts or pumping methods generally shift ___ or ___ down to lower ___ pressures. This is due to providing additional ___ to lift fluids when the ___ cannot provide adequate pressure.
TPC (tubing performance curve) or OPR
bottom hole
pressure
reservoir
Nodal Analysis (Two Phase): Gas Lift
Injection of gas does what to fluid?
Gas injection makes the hydrostatic column lighter allowing for the liquid to be lifted up and out of the well. Decreasing the fluid density will decrease the gravitational pressure losses allowing for production to occur.
Nodal Analysis (Two Phase): Gas Lift
As GLR increases due to gas injection, how does the OPR change?
The OPR shifts downwards. Although, at very high injection, the OPR will shift upwards due to the pressure increasing from frictional losses increasing. Therefore, the production will decrease, as the operational point moves up on the IPR curve.
Nodal Analysis (Two Phase):
Free flow =
Pumped flow =
No artificial lift
Artificial lift used
Nodal Analysis (Two Phase): Separator Pressure
How does increasing separator pressure affect the OPR?
Increasing separator pressure shifts the OPR upwards. Therefore, it decreases the production.
Nodal Analysis (Two Phase): Water Cut Effect
Increasing WC, increases the mixture ___ and ___ pressure gradient
Increasing WC, can decrease the oil-water mixture ___ and ___ pressure gradient
density
gravitational
viscosity
friction
T/F: The assumption of no-slip can be applied for dispersed bubble flow pattern
True
Nodal Analysis (Two Phase): Water Cut Effect
If the fluid velocity is too ___, the effect on OPR can shift ___ to higher ___ rates
high
downwards
production
Nodal Analysis: Stability
When a production system is disturbed from its equilibrium point, it is called
Stable if:
Unstable if:
Stable if it restores equilibrium
Unstable if it diverges from equilibrium solution
Nodal Analysis (Two Phase): Water Cut Effect
Commonly, as WC increases, the ____ losses increase due to increased density causing the OPR to shift ___ to lower ___ rates.
gravitational
up
production
T/F: The flow patterns in upward inclinations are similar to the case of horizontal flow
False
T/F: Zero pipe roughness means the friction factor is 0
False
T/F: When both IPR and OPR have negative slopes, the nodal analysis solution is unstable
True
For two-phase liquid-gas flow in vertical wells, generally
gravitational pressure gradient in the tube is proportional to the liquid holdup
Multiphase flow includes:
1.
2.
3.
4.
1. gas-liquid two phase flow
2. oil-water two phase flow
3. gas-oil-water three phase flow
4. two or three phase flow with sand particles or deposits
Multiphase flow is ___ in production and transportation. Therefore, basic design parameters such as ___ gradient and ___ are essential to understand flow assurance issues
inevitable
pressure
holdup
Steady state flow ________ with time
doesn't change
Transient state flow _________ with time
changes
Flow can be transient for many different reasons which allows for the classification as:
1.
2.
1. natural or imposed transients
2. fast or slow transients
Most of production occurs under ___________ state conditions
steady
Piping is typically designed based on ___ state flow
steady
Natural transient flow causes
severe slugging in flow line or riser systems
Terrain slugging from natural transients can be within:
1.
2.
3.
1. offshore pipelines
2. onshore pipelines
3. horizontal wells
Imposed transients are due to:
1.
2.
3.
1. line shut in and startup
2. intentional change in operating conditions
3. unintentional change in operating conditions
Imposed transients: Line shut in and start up
1. Causes fluids to ___ in the line due to gravity
2. Liquid-gas and liquid-liquid ___ and ___ especially at low spots
3. Restart can generate large ___
4. Restart can be the trigger of flow ___ problems
1. redistribute
2. segregation and accumulation
3. slug
4. assurance
Imposed transients: Intentional change in operating conditions
1. ___ rate changes
2. Downstream ___ changes
3. ___
1. flow
2. pressure
3. pigging
Imposed transients: Unintentional change in operating conditions
1. Pump/compressor ___
2. ___, ___
1. upsets
2. ruptures, leaks
No-slip Holdup:
The assumption is no slip between phases, phases travel at same velocity
Liquid Holdup
Fraction of the pipe cross section is filled with liquid
Void fraction
fraction of pipe occupied by the gas phase
Slippage is:
1. Fundamental phenomenon in ___-___ systems
2. The difference in ___ of liquid and gas phases
3. Higher slippages causes higher liquid ___ in pipe
4. Liquid velocity higher only in some ___-inclined pipes
1. gas-liquid
2. velocities
3. accumulation
4. downwards
Slippage commonly means ___ is flowing faster than ___
gas
liquid
What is the equation for slip velocity?
Vslip = Vg - Vl
Slippage:
In downward pipes liquid flow faster due to ___ pull in some cases
gravitational
Superficial velocities
Velocity of a phase assuming it flows through entire pipe cross section alone
In-situ velocity
actual velocity of both phases
Slip velocity
The difference between the actual gas and liquid phase velocities
No slip flow parameters (V)
V_l = V_g
No slip flow parameters (H)
H_l = lambda_l
slip flow parameters (V)
V_l < V_g
slip flow parameters (H)
H_l > lambda_l
Watercut (WC) is also known as
water fraction (f_w)
Effective mixture viscosity ___ sharply as the water cut approaches the inversion point due to ___ dispersions (smaller droplet sizes) having higher viscosities. The deviation of fluid behavior from ___ to ___ cause this to occur.
increases
tighter
Newtonian to non-Newtonian
water dispersion is where
one phase is dispersed as droplets into the other phase (the continuous phase)
Requirements for forming a dispersion:
1.
2.
1. two immiscible fluids
2. Continuous agitation to disperse on liquid into small drops. Agitation comes from the turbulent flow.
Inversion point is the water cut needed to switch from ___-continuous to ___-continuous
oil-continuous
water-continuous
Inversion point depends upon the ___ viscosity. Generally ___ viscosity is larger than ___ viscosity
oil
oil
water
If 100% oil, viscosity of liquid =
If 100% water, viscosity of liquid =
oil viscosity
water viscosity
If WC is < WC_inversion
oil continuous
if WC is > WC_inversion
water continuous
What is the difference between emulsion and dispersion?
Emulsion occurs due to surfactants which cause a stable combination of fluid. Dispersion is not very stable.
Emulsion is a chemical reaction, dispersion is a mechanical reaction.
Dispersion separates when flow stops while emulsion does not separate when flow stops (makes separator separation more difficult)
flow patterns are
physical distribution of gas and liquid phases in pipe
Controlling parameters of flow patterns: (4)
1. gas and liquid flow rates
2. inclination angle
3. diameter
4. phase densities
Phase densities of liquids do not change much, but ___ density can change
gas
Inclination has caused flow assurance issues in horizontal wells for what reason?
It is due to deviation of the wellbore within the horizontal. These deviations create high and low spots that affect the flow assurance of the fluid.
Main studies of flow pattern is for ___ or ___ pipes
horizontal or vertical
Types of inclined flow:
1.
2.
1. Upward inclination (similar to upward vertical flow)
2. Downward inclination (similar to horizontal flow)
Types/categories of horizontal flow patterns: (4)
1. Stratified or wavy flow
2. Plug or slug flow
3. Annular or mist flow
4. Bubbly or dispersed bubble flow
Horizontal Flow Patterns:
Stratified Flow (Smooth vs. wavy)
Smooth = full separation of phases by gravity, liquid on bottom and gas on top, no waves present
Wavy = same separation but with interfacial waves
Horizontal Flow Patterns:
Plug/Slug flow
intermittent flow of 1) full body of liquid and 2) Taylor bubble and liquid film
Horizontal Flow Patterns:
Annular/Mist flow
High velocity gas core flow, with liquid flowing as a film on the wall (annular) or entrained droplets within gas (mist) or both (annular mist)
Horizontal Flow Patterns:
Bubbly/Dispersed Bubble flow
high velocity liquid flow, with gas broken into small bubbles that are carried by the liquid
Horizontal Flow:
Transition between ___ and ___ or ___ ___ flow becomes very large with smallest upwards ___ which creates a flow called ___-___
slug and annular or stratified wavy
inclination
pseudo-slug
Vertical Tubing Flow Patterns:
Flow is mostly dominated by ___, except in high ___ rates which causes ___ flow
gravity
gas
annular
Vertical Tubing Flow Patterns:
Bubbly flow
At very low gas rates, small gas bubbles are traveling along within the liquid film with low slippage and low velocity
Vertical Tubing Flow Patterns:
Slug flow
With increase of V_sg, gas bubbles coalesce and form intermittent flow of Taylor bubbles and liquid film. The flow basically gas bubbles followed by liquid bubbles.
Vertical Tubing Flow Patterns:
Churn flow
With more increase of V_sg, gas bubbles break into the slug body and disrupt the continuous slug, forming irregular churn flow with high slippage
Vertical Tubing Flow Patterns:
Annular flow =
When V_sg becomes high enough, the gas core can continuously carry the liquid film upward creating annular flow
Vertical Tubing Flow Patterns:
The determining factor is the ___ flow. As ___ flow increases, ___ decreases and flow becomes more ___ dominated
gas
gas
holdup
gas
Horizontal Piping:
Larger ID results in more ___ flow
Smaller ID results in more ___ flow
stratified
slug
Horizontal Piping:
Downward/horizontal results in more ___ flow
Upward/vertical results in more ___ flow
stratified
slug
Main objective of modeling is to obtain ___ and ___ gradients
pressure and temperature
As fluids move upwards gas can come out of solution, causing
two-phase flow
To model pressure and temperature gradients, what is required? (3)
Fluid properties, flow rates, and pipe geometry
Three main modeling approaches are:
1. Homogenous model
2. Drift flux model
3. Two-fluid model
Homogenous Flow:
What is the flow structure?
What is neglected or assumed?
How does it happen?
The flow structure is where two phases flow in the same speed.
Slippage is neglected and it is assumed the phases are moving in no-slip conditions.
It happens when one phase is finely dispersed within the other phases and there are large interfacial areas. It occurs when the high speed of one phase crease turbulence to disperse the other phase within it.
Homogenous Flow:
For gas-liquid two-phase flow, homogenous assumption is only valid for ___ ___ or ___ flow patterns.
dispersed bubble (high liquid speed) or mist (high gas speed)
Vertical Well Production:
Pressure at the bottom of the well may be high enough to ensure ___ phase. Although, as the fluid moves upwards, ___ can break out of solution resulting in two phase flow as pressure decreases.
single
gas
Vertical Well Production:
Changes in in-situ fluid properties and flow rates can change ___ pattern and ___ gradient along the well.
flow
pressure
Vertical Well Production:
The main factors of changes in flow pattern and pressure gradient along a well are: (2)
Phase envelope and gas expansion
In general, from bottom to top of a well, we can have what flow: (5)
1. single phase oil
2. bubbly flow
3. slug flow
4. churn flow
5. maybe annular or mist flow
Pressure traverse was used as a:
popular solution to tabulate numerical results from the program into charts before computers were widespread. It used correlations of fluid properties and pressure gradient.
Curves in Pressure Traverse Charts are functions of
tubing/pipeline ID, liquid flow rate, WC, avg. flowing temp or temp gradient, and fluid properties of oil, gas, and water
Correlation for no slip, no flow pattern:
Category?
Includes?
Category A
Homogenous mixture, and mixture friction factor correlations
Correlation for slip, no flow pattern:
Category?
Includes?
Category B
Correlations for both liquid holdup and friction factor
Correlation for slip & flow pattern:
Category?
Includes?
Category C
Correlation for flow pattern, correlations of both liquid holdup and friction factor for each flow pattern
what category is Hagedorn & Brown
Category B
what is Hagedorn & Brown based on?
It is based on data obtained from 1500 ft vertical experimental well
Hagedorn & Brown considers _____ liquid holdup measurement
no
Hagedorn & Brown considers _____ data points
360
Hagedorn & Brown:
After assuming a friction factor correlation what occurs?
"pseudo liquid holdup" values for each test are determined to match measured pressure gradients calculated
Beggs & Brill is based on
air-water and small pipe diameter experimental system
Beggs & Brill is valid for all ___ angles, but it only considers ___ flow patterns.
inclination
horizontal
Beggs and Brill:
For each horizontal flow pattern, ___ angle corrections are made
inclination
Beggs and Brill uses ___-slip holdup and ___ number
no
Froude
What is the main difference between Hagedorn & Brown and Beggs & Brill correlations?
H&B is based on vertical wells while B&B is based on horizontal wells
T/F: An oil-water dispersion's viscoisty is minimized at the inversion point
False
T/F: Nodal analysis of oil wells is commonly conducted with the node placed at the well bottomhole
True
T/F: Proper sizing of the wellbore tubing can help shift down the OPR curve and increase the production
True
T/F: If the fluid is incompressible, the flow pressure gradient can be commonly assumed constant along the pipe
True
T/F: In vertical wells, pressure drop is mostly dominated by friction
False
As more gas breaks out of solution, what happens to the density of the fluid?
It becomes lighter
Pressure Traverse:
Large pressure drops near the ___ of the well, but as you get ___ to the surface there is not as much change
bottom
closer
When there is no gas, ___ ___ is constant due to oil being ___. Therefore, GLR =
pressure gradient
incompressible
GLR = 0
When J changes, what does it affect in IPR and OPR plots?
It affects IPR. OPR does not change when J changes.
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