advanced production operations - fall 2006 - final exam
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ENCH 619 Final ExamDecember 6, 2006
NAME______________________________________ U OF C STUDENT ID__________________________
Duration – 3 hours
Closed Book, Closed Notes
Multiple Choice – 50 Marks Possible =_________
Written Answer – 20 Marks Possible = __________ Computational – 30 Marks Possible = ___________
TOTAL __________
Equations and constants which may be of use
)(2.2)(log25.0 10 wiair i S K APT
air Hgair hg
RF RF
air HgC
RF C
ABS PP
cos
cos
s
ww er r '
w
a
a
a
r
r n
k
k k S
BPRF LghP f fpcirc
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ghPC G=9.81 m/s2
Pc = Pnw-PwPV=nZRT
R=8.3145 kJ/Kmol.K
---------------------------------------------------------------
MULTIPLE CHOICE SECTION – Pick the single
BEST answer to each question. Total Possible Marks
this Section = 50, one, mark per question unlessotherwise indicated.
1. During the transient flow period of a well, what type of skin factor is the mostimportant in potentially reducing the production rate of the wellbore
a. Vertical partial penetration skin
b. Areal partial penetration skin
c. Near wellbore Hawkins type skind. All of a-c
e. None of the above
2. A wellbore has a radius of 160 mm. Drilling induced formation damage causes a
near wellbore skin factor of 5.6 to be created. If we wanted to model this wellbore
using the concept of a zero skin, but with a revised radius to account for thedamage, what would the apparent radius of the wellbore have to be;
a. 0.296 mm
b. 0.592 mmc. 43.26 m
d. 21.63 m
e. None of the above
3. A drilling fluid reacts with clay in a vertical open hole well and reduces effectiveformation permeability to oil to in a radius of depth 35 cm from the center of a
200 mm diameter wellbore. If the initial undamaged formation permeability has avalue of 465 mD, what is the value of the permeability to oil in the damaged zone
if a skin of 16.8 is determine from pressure transient analysis of the wellbore?
a. 0.036 mD b. 32.26 mD
c. 27.45 mD
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d. 154.62 mD
e. None of the above
4. Which of the following cations would, at a given identical concentration in a
completion fluid, have the maximum stabilizing capacity for reducing potential
damage due to clay swelling and clay deflocculationa. NH4
b. K
c. Na
d. Ca
5. Match the following damage mechanism to the specific broad classification of
formation damage into which it falls, classifications can be Mechanical, Chemicalor Biological formation damage (3 marks);
a. Phase trapping is a ________________________ damage mechanism
b. The growth SRB is a _________________ damage mechanism
c. Surfactant adsorption causing a wettability change to oil wetness in a oil production well is a ___________________damage mechanism
d. Clay swelling is a ___________________ damage mechanism
e. Proppant crushing upon fracture closure is a ________________ damagemechanism
f. Diamondoid precipitation from a rich gas condensate is
a__________________damage mechanism
6. A porous media with an average pore throat diameter of 15 microns is pulsed at a
high flow rate which migrates in-situ kaolinite clay – assuming laminar flowconditions exist in the pore system, what size of particles WOULD NOT have a
plugging tendency in the pore throats.
a. Particles smaller than 1 micron in diameter b. Particles smaller than 3 microns in diameter
c. Particles smaller than 5 microns in diameter
d. Particles smaller than 10 microns in diameter
e. Particles smaller than 15 microns in diameter
7. In a formation contain a combination a illite and kaolinite clay that is loosely
cemented in the pore system, in strongly oil wet rock, fines migration would bemost probable with;
a. High fluid loss rates of oil based drilling mud filtrate
b. High fluid loss rates of water based drilling mud filtratec. High gas production rates
d. High water production rates
e. All of the above
8. If we desire a gel chemical drilling mud which contains clays to maintain its
proper fluid rheological properties by keeping the clay in a dispersed
(deflocculated) state, we would want to maintain the pH in a;
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a. Acidic state
b. Neutral state
c. Basic stated. Comatose state
9. The type of drilling bit which tends to generate the greatest degree of friction and potential for glazing is a;
a. Rotary drilling bit
b. Percussion drilling bit
c. Air Hammer d. Both b and c
10. The only practical method of removing very small drill solids from a drilling mudsystem (solids of less than 3 microns in diameter) is;
a. Double centrifuge
b. Shale shakers
c. Static settling tanksd. Dump a portion of the mud and replace with fresh fluid
e. All of the above
f. None of the above
11. Which of the following materials serves as both a bridging and weighting agent in
many drilling fluid systems;a. Barite
b. Calcium carbonate
c. Bentonited. Hematite
e. Cellulosic fibre
12. When drilling in a near balanced condition (100 kPa overbalanced), what
permeability range of formation will establish the best sealing (low permeability)
filter cake most rapidly with a given drilling fluid system;
a. 2500 mD rock b. 500 mD rock
c. 1 mD rock
d. 0.01 mD rock
13. Phase trapping of water based fluids can occur in;
a. Tight, low initial water saturation reservoirs b. Strongly oil wet sandstones
c. Strongly oil wet carbonates
d. All of the above
e. None of a-d
14. A capillary subnormal water saturation is created when
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a. A very large transition zone is observed in the reservoir above a water-gas
contact
b. No mobile water is present in the reservoir c. Mobile water is present in the reservoir
d. The reservoir is subnormally pressured
e. Regional gas migration effects dehydrate the reservoir sediments to a levelless than would be expected for the capillary geometry of the rock and no
free water is in contact with the formation to replace the evaporated water
phase
f. None of the above
15. Mixed wet porous media typically has;
a. Initial water saturations that correlate with permeability and the degree ofmicroporosity in the system
b. Very high electrical resistivity due to a discontinuous water phase
c. Strongly oil wet behavior in the dominant flow channels
d. Very low initial water saturatione. All of a to d
f. Only a and c
g. None of the above
16. Based on the APT index computed for a low water wet intercrystalline Grand
Rapids sandstone formation with an average uncorrected air permeability value of3900 mD and average initial water saturation of 12 % we would expect that;
a. Water based phase trapping effects could be significant
b. Oil based phase trapping effects could be significantc. Both water and oil based phase trapping effects would likely be significant
d. Water based phase trapping effects would not be significant
17. Countercurrent imbibition while underbalanced drilling would potentially be an
formation damage issue when;
a. Drilling with an oil based fluid in a normal irreducible water saturation
level gas reservoir that is water wet b. Drilling with an water based fluid in a normal irreducible water saturation
level gas reservoir that is water wet
c. Drilling with an water based fluid in a subnormal water saturation levelgas reservoir that is oil wet
d. Drilling with an water based fluid in a subnormal water saturation level
gas reservoir that is water wete. None of the above
18. In general, which of the following systems would have the lowest interfacial
tension at 20 MPa and 100 deg Ca. Water – methane gas
b. Oil – methane gas
c. Water – CO2 gas
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d. Oil – CO2 gas
e. Methanol - nitrogen
19. Glazing induced formation damage is most significant in which of the following
set of circumstances;
a. Drilling with pure gas in a carbonate formation that will be completedopen hole
b. Drilling with gas plus a small amount if liquid phase (mist drilling) in a
sandstone formation that will be completed open hole
c. Drilling with pure gas in a sandstone formation that will be cased and perforated
d. Drilling with gas plus a small amount of liquid (mist drilling) in a
carbonate formation that will be completed open holee. Drilling with pure gas in a sandstone formation that will be completed
open hole
f. None of the above
20. Clay deflocculation is caused by;
a. Disruption of hydrogen bonding forces that result in a repulsion of cation
layers that surround individual clay particles b. Substitution of water molecules into the clay matrix causing expansion of
the clay
c. Thin film adsorption of hydrogen ions on the surface of the clayd. Rapid reductions in the fluid pH
e. Increases in fluid salinity
f. None of the above
21. Clay surfaces tend to be;
a. Always oil wet b. Cationic in nature
c. Anionic in nature
d. Nonionic in nature
e. None of the above
22. Naturally radioactive scales would be
a. Calcite b. Barium Sulphate
c. Dolomite
d. Strontium Sulphatee. Iron Sulphate
f. Pyrite
g. B and d
h. A and ci. None of the above
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23. Which of the following scales would be insoluble in conventional hydrochloric
acid?
a. Calcite b. Iron Sulfide
c. Iron Oxide
d. Dolomitee. None of the above
24. With respect to clay stabilizing ability (for swelling and deflocculation) – which
of the following ranking of ions is correct with respect from going to leaststabilizing potential to most stabilizing potential when in aqueous solution
a. Calcium, Magnesium, sodium, potassium
b. Quaterny amine, sodium, calcium, magnesiumc. Sodium, potassium, magnesium, quaterny amine
d. Sodium, calcium, potassium, quaterny amine
e. None of these are in the right order
25. The OriEmulsion process in Venezuela, where heavy bitumen is emulsified with
water to reduce viscosity to allow transportation of the oil via a conventional
pipeline is a good example of what type of emulsion;a. Oil in water emulsion
b. Gas in oil emulsion
c. Micellar emulsiond. Water in oil emulsion
e. None of the above
26. Drilling with a fluid of density 1150 kg/m3 at a depth of 2500 m in a normally
hydrostatically pressure formation (assuming friction and backpressure effects are
zero) would result in the drilling operation being classified as a;a. Induced underbalanced drilling operation
b. Overbalanced drilling operation
c. Flow drilling operation
d. Balanced drilling operatione. None of the above
27. Which types of potential damage mechanisms can occur even during a perfectlyexecuted underbalanced drilling operation?
a. Gravity drainage into macroporous features (large fractures, vugs)
b. Countercurrent imbibtionc. Mashing
d. Bit Jetting
e. Localized depletion effects leading to possible overbalanced incidents
f. All of the above
28. Which of the following factors does not have a direct impact on capillary
pressure;
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a. Pore geometry
b. Wettability
c. Viscosityd. Wettability
e. All of the above
29. In a mixed wettability reservoir;
a. The microporosity is oil wet and the macroporosity is water wet
b. The microporosity is water wet and the macroporosity is oil wet
c. The microporosity has portions that are both water and oil wet dependingon mineralogy and the macroporosity is water wet
d. The macroporosity is water wet and the microporosity can be water or oil
wete. None of the above
30. Hole cleaning during drilling operations is most effective when
a. The fluid used to drill is the same fluid base as the wettability of heformation
b. The fluid used to drill is a non wetting fluid with respect to the wettability
of the formationc. We use a percussion hammer drilling operation
d. When we do not rotate or slide the drill string
e. None of the above
31. Assuming a gas reservoir containing gas of density 200 kg/m3 and water of
density 1100 kg/m3 and a capillary pressure curve that indicates that at a capillary pressure value of 75 kPa the water saturation is 45%, at what height above a free
water contact at the base of the gas reservoir would a 45% water saturation occur;
a. 0.085 m b. 0.0085 m
c. 8.5 m
d. 7.0 m
e. 0.0070 m
32. In a two phase underbalanced drilling operation, when operating in the frictiondominated flow regime, when at a constant liquid injection rate the gas rate is
increased the bottomhole pressure will;
a. Increase b. Decrease
c. Remain unaltered
d. Well – what other choice is there?
33. A particular type of damage has the potential to cause simultanoues issues with
plugging due to polymer adsorption issues, corrosion of metallic surfaces and
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souring of the reservoir by H2S gas generation – this damage mechanism would
be associated with;
a. Aquathermolysis reactions b. Aerobic bacterial growth
c. Anaerobic bacterial growth
d. Acid reaction with carbonate and sulphur compounds in crude oilse. Boiling of frogs
f. None of the above
34. As a result of natural frictional flow effects, as a perfectly horizontal well isdrilled underbalanced, and if a constant level of underbalance pressure is
maintained at the drill bit as the well gets longer as drilling proceeds, a section of
the well that was previously penetrated will always have an effective level ofunderbalance pressure that is;
a. Constantly increasing
b. Constantly decreasing
c. Remaining the same
35. In an oil wet rock containing a 15% water saturation in a condition where a
positive (+) value of capillary pressure is present the effective pressure in the oil phase is;
a. Lower than the water phase
b. Higher than the water phasec. The same as the water phase
36. For a tight, water wet gas reservoir with an initial permeability of 0.1 mD and an
initial water saturation of 85% we would expect that formation damage due to
water based phase trapping would bea. A Major problem
b. A minor problem
c. Not significant
d. None of the above
37. A gas system which has a steady gas-liquid ratio of 5 stb of condensate liquid per
MMscf of gas at separator condition would most likely be classified as a;a. Retrograde condensate gas system
b. Dry gas system
c. Near critical oil systemd. Sub dewpoint gas system
e. None of the above
38. As temperature increases, both sandstone and carbonate surfaces tend to;a. Become more acidic
b. Become more basic
c. Become more oil wet
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d. Become more water wet
e. None of the above
39. If the characteristic curvature of an interface is zero (e.g. – the interface between
two fluids is perfectly flat), it is an indication that there is;
a. No capillary pressure b. The surfaces the interface contacts are perfectly neutral wet
c. The IFT is zero
d. The density of the two fluids is the same
e. A and Bf. None of the above
40. Transient wettability modifiers are used toa. Reduce clay swelling problems
b. Reduce water based phase trapping problems
c. Reduce clay deflocculation
d. Remove residual oile. Break stable emulsions
41. Which of the following completion types, in a reservoir with 10 m of net pay,would have the greatest surface area exposure for fluid flow which would allow
for minimum flow velocity if fines migration problems at low interstitial velocity
were a major formation damage concern;a. 800 m long, 200 mm diameter horizontal well completed open hole
b. Cased and perforated vertical well, 10 shots/meter
c. Open hole vertical welld. Cased vertical well completed with a 75 tonne hydraulic sand fracture
treatment
42. Which gas composition would represent the typical production stream from a
membrane nitrogen generation unit used for underbalanced drilling operations;
a. 99.8% N2, 0.2% O2
b. 85% N2, 15% O2c. 97.5% N2, 2.5% O2
d. 79% N2, 21% O2
e. 100% methane
43. High concentrations of resin type components in crude oils tend to reduce
potential issues with;a. Emulsion formation
b. Asphaltene precipitation
c. Paraffin deposition
d. Scale formatione. All of the above
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44. When a fractured well’s production rate is limited by the ability of the formation
to flow reservoir fluid into the fracture, the process is said to be;
a. Fracture face limited b. Fracture conductivity limited
c. Permeability limited
d. Porosity limited e. Just plain limited
45. Proppant resistance to crushing is improved by;
a. High proppant angularity b. Low proppant sphericity
c. High proppant sphericity and roundness
d. Low proppant roundnesse. None of the above
46. A chelating agent in a 15% HCl acid system is used primarily to;
a. Increase acid viscosity b. Retard acid reaction rate
c. Bind up free iron to prevent emulsions and precipitates
d. Prevent fluid losse. Penetrate organic coatings on the rock surface to allow better acid contact
47. For a uniform intergranular sandstone of permeability of 100 mD, theapproximate diameter of the average pore throat would be about
a. 1 micron
b. 5 micronsc. 10 microns
d. 50 microns
e. 100 microns
48. A conventional water-polymer drilling mud is a good example of a;
a. Water in oil emulsion system
b. Oil in water emulsion systemc. Water external emulsion system
d. Oil external emulsion system
e. None of the above
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Written Answer
1. Briefly explain how an air hammer can reduce glazing inducing formationdamage in pure air drilling applications in contrast to a conventional rotary type
drill bit (3 Marks).
_____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________ _____________________________________________________________________
2. List three possible methods for the separation of oil from a viscous water internalor water external emulsion.
________________________________________________________________________
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3. The following diagram illustrates an underbalanced drilling application in a
subnormally saturated tight gas reservoir. The pressure curve for the pressure inthe gas phase in the wellbore and in the formation adjacent to the wellbore is
given. Assuming that the reservoir pressure is 10,000 kPa, that the bottomhole
pressure while drilling is 7,000 kPa and that the reservoir is undersaturated with
water so that the capillary pressure at 10% initial water saturation in the matrixhas a value of 5000 kPa, draw the pressure curve for the water phase at time = 0
when the water + nitrogen based fluid being used to drill the well contacts theformation and explain why (and show on the figure) countercurrent imbibition of
water into the matrix of the rock would occur and why it occurs (6 marks).
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________________________________________________________________________
________________________________________________________________________ ________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
4. A well is drilled and completed open hole in a formation with the following
characteristics (8 marks)a. Depth 2900 m
b. Pressure 19500 kPa
c. Temperature 102 deg Cd. Type – intercrystalline dolomite containing 35 micron to 250 micron
diameter natural fractures
e. Brine composition – 278,000 ppm NaClf. Wettability – strongly oil wet
g. Composition, 100% dolomite
h. Initial water saturation – 8%
i. Air permeability – 17 mD
j. In-situ permeability – 6 mDk. Confining stress – 72,000 kPa
l. Reservoir fluid – 32 deg API gravity oil
If we were to design a conventional overbalanced drilling program, provide your
recommendations for what you feel would be the optimum system for such a reservoir,describe the types of damage to which you feel this reservoir may be susceptible and how
we would design the system to avoid or reduce the impact of these damage
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mechanisms._____________________________________________________________
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Suppose we decided to use underbalanced drilling instead, what/how would your
recommendations for the drilling operation and fluid type to be used change from theoverbalanced case, once again comment on typical damage mechanisms and how you
feel your design would reduce these in the most economic fashion
possible?________________________________________________________________ ________________________________________________________________________
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___
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COMPUTATION SECTION
1. Given the following set of capillary pressure curves and gas-water relative permeability curves for a water wet gas reservoir application with the following
properties;
Depth 2235 mPressure 21,000 kPag
Temperature 76 deg C
Water composition – 154,000 ppm NaClGas-Water IFT 54 mN/m
Water Density at T and P = 1089 kg/m3
Gas Density at T and P = 156 kg/m3Gas Composition – 89% methane, 8% ethane, 3% propane
Permeability – 1.8 mD
Porosity – 16%
Initial water saturation – 14%Drilling fluid density – 1200 kg/m3
Hole diameter – 200 mm
Gas-Water Capillary Pressure vs. Water Saturation
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
0 0.2 0.4 0.6 0.8 1
Water Saturation - Fraction
C a p i l l a r y P r e s s u r e - k P a g
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Gas-Water Relative Permeability Curves
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8
Water Saturation - Fraction
R e l a t i v e P e r m e a b i l i t y - F r a c
Gas Phase
Water Phase
a. Assuming a total of 2.4 m3 of water based drilling fluid are lost to the formation during
the overbalanced drilling process, and assume perfectly uniform invasion around the
wellbore which comprises 5 meters of pay, compute the radial depth of invasionassuming that the trapped gas saturation as generated in the set of relative permeability
curves above is generated in the invaded zone surrounding the wellbore and that the
entire zone is initially at a uniform initial water saturation as given in the initial dataset (8
marks).
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b. Assuming that on the cleanup phase a effective drawdown pressure of 3000 kPa can be
applied to the reservoir uniformly in the water filtrate invaded zone, based on the
provided information, what would be the effective permeability of the invaded zone andhow much reduction in permeability in the invaded zone could be attributed to phase
trapping effects (7 marks).
c. Given the previously calculated information, compute the skin factor that would be
present surrounding the wellbore caused by the phase trap induced damage (if any –
assume that no other types of formation damage occur that would reduce the permeability
of the formation)(5 marks).
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1. 2. Given the following relationship for computation of bottomhole pressure;
Consider the following deviated wellbore;
Given that the;
Total length of the deviated well from surface to the base of the well is 2400 m.The true vertical depth (TVD) of the Overpressured Zone #1 is 1000 mThe pressure of overpressured zone #1 is 12,600 kPaa
The pressure of the production zone is 10,800 kPaaThe circulating friction pressure gradient is 0.245 kPa/m of circulating path length
The surface backpressure is held constant at 400 kPaa
The value of g = 9.81 m/s2
Please compute;
a. The necessary mud weight in kg/m3 required to give a safe overbalance pressure
of 1,500 kPaa when penetrating the uphole overpressured zone #1 ( 4 marks)
30 Deg ZONE 1 – OVER PRESSURED
BPRF LghP f fpcirc
Production Zone
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b. If this same mud weight is maintained to the base of the well in the productive
zone, what will the level of overbalance or underbalance pressure be in the
production zone. (4 marks)
c. How would this condition possibly affect the ultimate productivity of the
producing interval? (1 mark)
d. What could be a possible technique to reduce/eliminate this problem while still
allowing us to safely drill through the overpressured uphole zone? (1 mark)
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