Abnormal Pressure 10.1- 1
1.10-1
Abnormal Pressure
Abnormal Pressure 10.1- 2
Abnormal Pressure
- Definition, Causes -
Normal Pore Pressures
Abnormal Pore Pressure Gradients
...
Abnormal Pressure 10.1- 3
Abnormal
Pressure
Gradients
Normal Pressure Gradients
West Texas: 0.433 psi/ft
Gulf Coast: 0.465...
Abnormal Pressure 10.1- 4
Pore Pressure vs. Depth
8 9 10 11 12 13 14 15 16
Pore Pressure Equivalent, lb/gal
0
5,000
10,000...
Abnormal Pressure 10.1- 5
Pore Pressure
Gradient
Fracture Gradient
Abnormal Pressure 10.1- 6
* Pore
Pressure
Gradients
* Fracture
Gradients
* Casing
Setting
Depths
Abnormal Pressure 10.1- 7
Some Causes of Abnormal Pressure
1. Incomplete compaction of sediments
 Fluids in sediments hav...
Abnormal Pressure 10.1- 8
Some Causes of Abnormal Pressure
3. Aquifers in Mountainous Regions
 Aquifer recharge is at hig...
Abnormal Pressure 10.1- 9
HIGH PRESSURE
NORMAL PRESSURE
Thick, impermeable layers of shale (or salt) restrict the movement...
Abnormal Pressure 10.1- 10
HIGH PRESSURE
NORMAL PRESSURE
Hydrostatic pressure gradient is lower in gas or oil than in wate...
Abnormal Pressure 10.1- 11
When crossing faults it is possible to go from normal
pressure to abnormally high pressure in a...
Abnormal Pressure 10.1- 12
Well “A” found only Normal Pressure ...
Abnormal Pressure 10.1- 13
σOB = p + σZ
σob
p σz
Abnormal Pressure 10.1- 14
?
Abnormal Pressure 10.1- 15
Indications of Abnormal Pore Pressures
Methods:
1. Seismic data
2. Drilling rate
3. Sloughing s...
Abnormal Pressure 10.1- 16
Indications of Abnormal Pore Pressures
Methods, cont’d:
7. Change in Mud properties
8. Temperat...
Abnormal Pressure 10.1- 17
Prediction and Detection of Abnormal
Pressure Zones
1. Before drilling
 Shallow seismic survey...
Abnormal Pressure 10.1- 18
Prediction and Detection of Abnormal
Pressure Zones
2. While drilling
 Drilling rate, gas in m...
Abnormal Pressure 10.1- 19
Prediction and Detection of Abnormal
Pressure Zones
3. After drilling
 Resistivity log
 Condu...
Abnormal Pressure 10.1- 20
. – .
SD000085.0
e41.0 −
=φ
Abnormal Pressure 10.1- 21
Decreasing ROP
What is d-
exponent?
Abnormal Pressure 10.1- 22
D - Exponent
The
drilling rate
equation:
Where
R = drilling rate, ft/hr
K = drillability consta...
Abnormal Pressure 10.1- 23
D - Exponent
If we assume that K = 1
and E = 1
Then
D
B
E
D
W
NKR 





=





...
Abnormal Pressure 10.1- 24
D - Exponent
A modified version of this equation
follows:












=
B
6
D10...
Abnormal Pressure 10.1- 25
Example
d may be Corrected for mud density
as follows:






=
)ppg(useinweightmudactua...
Abnormal Pressure 10.1- 26
Procedure for Determining Pore
Pressure From dc - Exponent
Calculate dc over 10-30 ft intervals...
Abnormal Pressure 10.1- 27
Procedure for Determining Pore
Pressure From dc - Exponent
dc - Exponent
Depth
Normal
Abnormal
...
Abnormal Pressure 10.1- 28
Procedure for Determining Pore
Pressure From dc - Exponent
If possible, quantify the magnitude ...
Abnormal Pressure 10.1- 29
In normally pressured
shales, shale
compaction increases
with depth
Abnormal Pressure 10.1- 30
Pore Pressure from
Resistivity
Shale resistivity plots
may be developed
from (i) logs or
(ii) c...
Abnormal Pressure 10.1- 31
From plot, Rn = 1.55 ohms
Robs = 0.80 ohms
From Eaton:
EATON
2.1
n
obs
n R
R
D
P
D
S
D
S
D
P
...
Abnormal Pressure 10.1- 32
Prediction of
Abnormal Pore Pressure
Resistivity of Shale
Temperature in the Return Mud
Drillin...
Abnormal Pressure 10.1- 33
EXAMPLE
Shale Resistivity
vs. Depth
1. Establish normal
trend line
2. Look for
deviations
(semi...
Abnormal Pressure 10.1- 34
Shale Resistivity
vs. Depth
1. Establish normal
trend line
2. Look for
deviations
3. Use OVERLA...
Abnormal Pressure 10.1- 35
Example
8.2 X
Why?
Abnormal Pressure 10.1- 36
Determination of Abnormal Pore
Pressure Using the dc - exponent
From Ben Eaton:
2.1
cn
c
n d
d
...
Abnormal Pressure 10.1- 37
Where
trendnormalthefromonentexpdd
plotfromentexpondactuald
psi/ftgradient,stressoverburden
D
S...
Abnormal Pressure 10.1- 38
Example
Calculate the pore
pressure at depth X using
the data in this graph.
Assume:
West Texas...
Abnormal Pressure 10.1- 39
Example
From Ben Eaton:
psi/ft5662.0
D
P
5.1
2.1
]433.00.1[0.1
d
d
D
P
D
S
D
S
D
P
2.1
2.1
cn
c...
Abnormal Pressure 10.1- 40
Example
lbm/gal9.10
12,000x0.052
6794
EMW
psi6794000,12x5662.0P
==
==∴
Abnormal Pressure 10.1- 41
E.S. Pennebaker
 Used seismic field data for the
detection of abnormal pressures.
 Under norm...
Abnormal Pressure 10.1- 42
E.S. Pennebaker
 Any departure from this trend is an
indication of possible abnormal
pressures...
Abnormal Pressure 10.1- 43
Interval Travel Time, µsec per ft
Depth,ft
Abnormal Pressure 10.1- 44
Ben Eaton
also found a way to determine pore pressure
from interval travel times.
Example:
In a...
Abnormal Pressure 10.1- 45
Ben Eaton
From Ben Eaton,
psi/ft0.6904
12,000
10,000
0.465]-[1.0-1.0
t
t
D
P
D
S
D
S
D
P
3
0.3
...
Abnormal Pressure 10.1- 46
Ben Eaton
From Ben Eaton
Note: Exponent is 3.0 this time,
NOT 1.2!
ρ = (0.6904 / 0.052) = 13.28...
Abnormal Pressure 10.1- 47
Equations for Pore Pressure Determination
2.1
c
c
n normald
calculatedd
D
P
D
S
D
S
D
P



...
Abnormal Pressure 10.1- 48
Pore Pressure Determination
of 48

Presiones Anormales - Abnormal Pressure

manual en ingles de presiones abnormales en pozos
Published on: Mar 4, 2016
Published in: Engineering      
Source: www.slideshare.net


Transcripts - Presiones Anormales - Abnormal Pressure

  • 1. Abnormal Pressure 10.1- 1 1.10-1 Abnormal Pressure
  • 2. Abnormal Pressure 10.1- 2 Abnormal Pressure - Definition, Causes - Normal Pore Pressures Abnormal Pore Pressure Gradients Fracture Gradients Mud Weights Casing Seat Depths What Causes Abnormal Pressure?
  • 3. Abnormal Pressure 10.1- 3 Abnormal Pressure Gradients Normal Pressure Gradients West Texas: 0.433 psi/ft Gulf Coast: 0.465 psi/ft Normal and Abnormal Pore Pressure Pore Pressure, psig Depth,ft 10,000’ ? ?
  • 4. Abnormal Pressure 10.1- 4 Pore Pressure vs. Depth 8 9 10 11 12 13 14 15 16 Pore Pressure Equivalent, lb/gal 0 5,000 10,000 15,000 20,000 { Density of mud required to control this pore pressure } Depth,ft Normal Abormal 0.433 psi/ft 8.33 lb/gal 0.465 psi/ft 9.0 lb/gal
  • 5. Abnormal Pressure 10.1- 5 Pore Pressure Gradient Fracture Gradient
  • 6. Abnormal Pressure 10.1- 6 * Pore Pressure Gradients * Fracture Gradients * Casing Setting Depths
  • 7. Abnormal Pressure 10.1- 7 Some Causes of Abnormal Pressure 1. Incomplete compaction of sediments  Fluids in sediments have not escaped and are still helping to support the overburden. 2. Tectonic movements  Uplift  Faulting
  • 8. Abnormal Pressure 10.1- 8 Some Causes of Abnormal Pressure 3. Aquifers in Mountainous Regions  Aquifer recharge is at higher elevation than drilling rig location. 4. Charged shallow reservoirs due to nearby underground blowout. 5. Large structures...
  • 9. Abnormal Pressure 10.1- 9 HIGH PRESSURE NORMAL PRESSURE Thick, impermeable layers of shale (or salt) restrict the movement of water. Below such layers abnormal pressure may be found.
  • 10. Abnormal Pressure 10.1- 10 HIGH PRESSURE NORMAL PRESSURE Hydrostatic pressure gradient is lower in gas or oil than in water.
  • 11. Abnormal Pressure 10.1- 11 When crossing faults it is possible to go from normal pressure to abnormally high pressure in a short interval.
  • 12. Abnormal Pressure 10.1- 12 Well “A” found only Normal Pressure ...
  • 13. Abnormal Pressure 10.1- 13 σOB = p + σZ σob p σz
  • 14. Abnormal Pressure 10.1- 14 ?
  • 15. Abnormal Pressure 10.1- 15 Indications of Abnormal Pore Pressures Methods: 1. Seismic data 2. Drilling rate 3. Sloughing shale 4. Gas units in mud 5. Shale density 6. Chloride content
  • 16. Abnormal Pressure 10.1- 16 Indications of Abnormal Pore Pressures Methods, cont’d: 7. Change in Mud properties 8. Temperature of Mud Returns 9. Bentonite content in shale 10. Paleo information 11. Wire-line logs 12. MWD-LWD
  • 17. Abnormal Pressure 10.1- 17 Prediction and Detection of Abnormal Pressure Zones 1. Before drilling  Shallow seismic surveys  Deep seismic surveys  Comparison with nearby wells
  • 18. Abnormal Pressure 10.1- 18 Prediction and Detection of Abnormal Pressure Zones 2. While drilling  Drilling rate, gas in mud, etc. etc.  D - Exponent  DC - Exponent  MWD - LWD  Density of shale (cuttings)
  • 19. Abnormal Pressure 10.1- 19 Prediction and Detection of Abnormal Pressure Zones 3. After drilling  Resistivity log  Conductivity log  Sonic log  Density log
  • 20. Abnormal Pressure 10.1- 20 . – . SD000085.0 e41.0 − =φ
  • 21. Abnormal Pressure 10.1- 21 Decreasing ROP What is d- exponent?
  • 22. Abnormal Pressure 10.1- 22 D - Exponent The drilling rate equation: Where R = drilling rate, ft/hr K = drillability constant N = rotary speed, RPM E = rotary speed expon. W = bit weight, lbs DB = bit diameter, in D = bit wt. Exponent or D - exponent D B E D W NKR       =
  • 23. Abnormal Pressure 10.1- 23 D - Exponent If we assume that K = 1 and E = 1 Then D B E D W NKR       =             = BD W log N R log D D BD W N R       =
  • 24. Abnormal Pressure 10.1- 24 D - Exponent A modified version of this equation follows:             = B 6 D10 W12 log N60 R log d
  • 25. Abnormal Pressure 10.1- 25 Example d may be Corrected for mud density as follows:       = )ppg(useinweightmudactual )ppg(gradientnormalforweightmud ddc 37.1 12 9 *82.1 12 9 dd.,g.e c =      =      =
  • 26. Abnormal Pressure 10.1- 26 Procedure for Determining Pore Pressure From dc - Exponent Calculate dc over 10-30 ft intervals Plot dc vs depth (use only date from Clean shale sections) Determine the normal line for the dc vs. depth plot. Establish where dc deviates from the normal line to determine abnormal pressure zone
  • 27. Abnormal Pressure 10.1- 27 Procedure for Determining Pore Pressure From dc - Exponent dc - Exponent Depth Normal Abnormal NormalTrend
  • 28. Abnormal Pressure 10.1- 28 Procedure for Determining Pore Pressure From dc - Exponent If possible, quantify the magnitude of the abnormal pore pressure using overlays, or Ben Eaton’s Method Pore Pressure Grad. Overburden Stress Grad. Normal Pore Pressure Grad. 2.1 c c n normald calculatedd D P D S D S D P                     −−=
  • 29. Abnormal Pressure 10.1- 29 In normally pressured shales, shale compaction increases with depth
  • 30. Abnormal Pressure 10.1- 30 Pore Pressure from Resistivity Shale resistivity plots may be developed from (i) logs or (ii) cuttings What is the pore pressure at the point indicated on the plot? [Assume Gulf Coast]. Depth=10,000 ft 0.2 0.5 1 2 3 10,000’ Depth
  • 31. Abnormal Pressure 10.1- 31 From plot, Rn = 1.55 ohms Robs = 0.80 ohms From Eaton: EATON 2.1 n obs n R R D P D S D S D P                   −−= ( ) 2.1 55.1 80.0 465.095.095.0 D P       −−= = 0.7307 psi/ft = 14.05 lb/gal P = 0.7307 * 10,000 = 7,307 psi 0.2 0.5 1 2 3 10,000’ Depth
  • 32. Abnormal Pressure 10.1- 32 Prediction of Abnormal Pore Pressure Resistivity of Shale Temperature in the Return Mud Drilling Rate Increase dc - Exponent Sonic Travel Time Conductivity of Shale
  • 33. Abnormal Pressure 10.1- 33 EXAMPLE Shale Resistivity vs. Depth 1. Establish normal trend line 2. Look for deviations (semi-log)
  • 34. Abnormal Pressure 10.1- 34 Shale Resistivity vs. Depth 1. Establish normal trend line 2. Look for deviations 3. Use OVERLAY to quantify pore pressure (use with caution) Pore Pressure (lb/gal equivalent) 16 14 12 10 9 ppg (normal)
  • 35. Abnormal Pressure 10.1- 35 Example 8.2 X Why?
  • 36. Abnormal Pressure 10.1- 36 Determination of Abnormal Pore Pressure Using the dc - exponent From Ben Eaton: 2.1 cn c n d d D P D S D S D P                   −−=
  • 37. Abnormal Pressure 10.1- 37 Where trendnormalthefromonentexpdd plotfromentexpondactuald psi/ftgradient,stressoverburden D S psi/ft0.465,or0.433e.g., areaingradientwaternormal D P psi/ftgradient,pressureformation D P ccn cc n −= −= = =      = 2.1 cn c n d d D P D S D S D P                   −−=
  • 38. Abnormal Pressure 10.1- 38 Example Calculate the pore pressure at depth X using the data in this graph. Assume: West Texas location with normal overburden of 1.0 psi/ft. X = 12,000 ft. X 1.2 1.5 dc
  • 39. Abnormal Pressure 10.1- 39 Example From Ben Eaton: psi/ft5662.0 D P 5.1 2.1 ]433.00.1[0.1 d d D P D S D S D P 2.1 2.1 cn c n =       −−=                   −−=
  • 40. Abnormal Pressure 10.1- 40 Example lbm/gal9.10 12,000x0.052 6794 EMW psi6794000,12x5662.0P == ==∴
  • 41. Abnormal Pressure 10.1- 41 E.S. Pennebaker  Used seismic field data for the detection of abnormal pressures.  Under normally pressured conditions the sonic velocity increases with depth. (i.e. Travel time decreases with depth) (why?)
  • 42. Abnormal Pressure 10.1- 42 E.S. Pennebaker  Any departure from this trend is an indication of possible abnormal pressures.  Pennebaker used overlays to estimate abnormal pore pressures from the difference between normal and actual travel times.
  • 43. Abnormal Pressure 10.1- 43 Interval Travel Time, µsec per ft Depth,ft
  • 44. Abnormal Pressure 10.1- 44 Ben Eaton also found a way to determine pore pressure from interval travel times. Example: In a Gulf Coast well, the speed of sound is 10,000 ft/sec at a depth of 13,500 ft. The normal speed of sound at this depth, based on extrapolated trends, would be 12,000 ft/sec. What is the pore pressure at this depth? Assume: S/D = 1.0 psi/ft
  • 45. Abnormal Pressure 10.1- 45 Ben Eaton From Ben Eaton, psi/ft0.6904 12,000 10,000 0.465]-[1.0-1.0 t t D P D S D S D P 3 0.3 n n =       =       ∆ ∆             −−= ( ∆t α 1/v )
  • 46. Abnormal Pressure 10.1- 46 Ben Eaton From Ben Eaton Note: Exponent is 3.0 this time, NOT 1.2! ρ = (0.6904 / 0.052) = 13.28 lb/gal p = 0.6904 * 13,500 = 9,320 psig
  • 47. Abnormal Pressure 10.1- 47 Equations for Pore Pressure Determination 2.1 c c n normald calculatedd D P D S D S D P                     −−= 2.1 n obs n R R D P D S D S D P                   −−=       ρ ρ             = ACTUAL NORMAL B 6 C * D10 W12 log N60 R log d 2.1 o n n C C D P D S D S D P                   −−= 0.3 o n n t t D P D S D S D P       ∆ ∆             −−=
  • 48. Abnormal Pressure 10.1- 48 Pore Pressure Determination

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