HW-5.
2: PORE PRESSURE PREDICTION—
EUGENE ISLAND 330
( POROSITY & V ELOCITY TO EFFECTIVE STRESS )
GOAL:
This homework supplements the discussion of pore pressure prediction discussed in
Chapter 5 (Flemings, 2021). We will predict pressure in the E.I.-330 A20ST well. See
Chapter 5, Figures 5.4-5.6, and 5.13, (Flemings, 2021)). We will use the normal compaction
trend parameters that you derived in HW5.1. We will both calculate by hand and use the
spreadsheet ‘NCT_Spread_sheet_and_PPP_EI-330’ to predict the pressure.
HUBBERT APPROACH
Use Hubbert’s approach to predict pore pressure in the E.I.-330 A20ST well. See Chapter 5,
Figures 5.4-5.6.
APPROACH:
𝜎𝑣′ = 𝜎𝑣 − 𝑢 Eq. 1
𝑢 = 𝜎𝑣 − 𝜎𝑣 ′ Eq. 2
𝑛 = 𝑛0 𝑒 −𝛽𝜎𝑣′ Eq. 3
1 𝑛
𝑢 = 𝜎𝑣 − 𝛽 ln ( 𝑛𝑜) Eq. 4
Based on the normal compaction trend shown in Figure 1 (i.e. 𝛽 = 2.15 𝑥10−4 𝑎𝑛𝑑 𝑛𝑜 =
0.38) (or based on your own interpreted NCT parameters from HW 5.1), calculate the pore
pressure (u) and fill in Table 1 and then plot these values in Figure 2. Double your value of
and re-calculate the pore pressure and place in the right column of Table 1.
EXERCISE:
Calculate the in-situ pressure at four different depths (Table 2) using Equation 4.
Depth (ft) n uh (PSI) v (PSI) u (Eq. 4) (PSI) u (Eq. 4) (PSI)
=0.000215 = 2
PSI-1
4714 0.243 2091 4123
6657 0.25 2951 5987
7231 0.31 3206 6543
7854 0.3 3482 7157
Table 2. Exercise for estimating pore pressure at EI-330.
HW-5.2: Pore Pressure Prediction Ch. 5 (revised 2/2021) Page | 1
© 2021 Flemings
0.38 Series1
0.36 Hubbert Expon.
(Series1)
0.34
0.32
n_sonic (-)
0.3
0.28
0.26
0.24
y = 0.384359e-0.000215x
0.22 R² = 0.958297
0.2
0 500 1000 1500 2000 2500
vh'
Figure 1: Compression curve from NCT Exercise. This analysis shows . 𝛽 =
2.15 𝑥10−4 𝑎𝑛𝑑 𝑛𝑜 = 0.38 (Eq. 3).
HW-5.2: Pore Pressure Prediction Ch. 5 (revised 2/2021) Page | 2
© 2021 Flemings
Pressure/Stress (1000 PSI)
0 1 2 3 4 5 6 7 8
4000
4500
5000
5500
Lithostat_psi
Hydrostat_psi
Depth (ft)
6000 Reservoir Pressures_psi
6500
7000
7500
8000
Figure 2: Plot your calculated pore pressures here. Compare your pressure prediction to the
observed pressures (red squares).
Compare your hand drawn result to the analysis of all the mudrock velocity data in the E.I.-
330 A20ST well by using the 3rd tab of the spreadsheet ‘NCT_Spread_sheet_and_PPP_EI-
330’. Make sure that you have the correct NCT parameters entered into the box on the right side of
the first tab (see Readme file for the spreadsheet).
HW-5.2: Pore Pressure Prediction Ch. 5 (revised 2/2021) Page | 3
© 2021 Flemings
Pore Pressure Bowers
(velocity to effective stress)
We will use the Bowers Approach (Bowers (1995)):
𝜎𝑣′ = 𝜎𝑣 − 𝑢 Eq. 1
𝑢 = 𝜎𝑣 − 𝜎𝑣 ′ Eq. 2
1
𝑉−5000 𝐵
𝑢 = 𝜎𝑣 − ( 𝐴 ) Eq. 3
Use the parameters that you have defined from your normal compaction trend analysis
(HW 5.1) or use the example below where A= 4.475, and B =0.852(Fig. 1) for the Eugene
Island 330 field.
3500
y = 4.475x0.8518
3000 R² = 0.9614
2500
V- 5000 (ft/sec)
2000
1500 Series1
Power (Series1)
1000
500
0
0 500 1000 1500 2000 2500
vh'
Fig. 3: Velocity vs. hydrostatic effective stress between 1000’ and 5300’ in the Pathfinder well.
HW-5.2: Pore Pressure Prediction Ch. 5 (revised 2/2021) Page | 4
© 2021 Flemings
1. Calculate the value of the pore pressure and fill in the table below and then plot these
values in Figure 2.
Depth (ft) Vel (ft/s) Uh (psi) v (psi) u v '
4717 8102 2189 4239
5258 8289 2440 4754
5945 8439 2757 5423
7210 6668 3345 6638
7854 6788 3644 7273
HW-5.2: Pore Pressure Prediction Ch. 5 (revised 2/2021) Page | 5
© 2021 Flemings
Pressure/Stress (1000 PSI)
0 1 2 3 4 5 6 7 8
4000
4500
5000
5500
Lithostat_psi
Hydrostat_psi
Depth (ft)
6000 Reservoir Pressures_psi
6500
7000
7500
8000
Fig. 4: Plot your calculated pore pressures here. Compare your pressure prediction to the
observed pressures (red squares).
Compare your hand drawn result to the analysis of all the mudrock velocity data in the E.I.-
330 A20ST well by using the 3rd tab of the spreadsheet ‘NCT_Spread_sheet_and_PPP_EI-
330’. Make sure that you have the correct NCT parameters entered into the box on the right side of
the first tab (see Readme file for the spreadsheet).
Flemings, P. (2021). A Concise Guide to Geopressure: Origin, Prediction, and Applications: Cambridge
Press.
HW-5.2: Pore Pressure Prediction Ch. 5 (revised 2/2021) Page | 6
© 2021 Flemings
