The mid depth for this interval is 972 m, with to1 horizon as the top of interval and
Paciran horizon as the bottom. For this interval (Fig 5.2), we can see that the ...
CHAPTER V RESULT AND DISCUSSION After doing all of the steps above, the result summary is : Table 5.1. Result Summary threshold
threshold
pressure
mid depth
velocity
pressure
max
int
horizon
(m)
(m/s)
(psi)
(psi)
1
to1-pcr
1174.5
1940
1271
4519
2
pcr-bo1
1811
2090
2830
5393
3
bo1-mnd
2695
2220
4248
7710
4
mnd-to2
3647.5
2280
8240
12603
5
to2-op2
3787
2300
7290
14271
6
op2-bo2
4329.5
2300
8610
15536
Interval 1 :
Figure 5.1 Pressure map for the first interval with velocity contour
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Figure 5.2. Pressure map for the first interval with depth contour
The mid depth for this interval is 972 m, with to1 horizon as the top of interval and Paciran horizon as the bottom.
For this interval (Fig 5.2), we can see that the overpressure zone almost covers the whole area with the magnitude of 1271 psi to 4519 psi. The threshold velocity is around 1940 m/s. The normal pressure zones are quite scattered in all area, but quite dominant in southern to western part of the map. The purple areas are the area with the lowest pressure and can be assumed as normal area. The area with the red color shows the high degree overpressure area, it can be seen in the center of the map and widely distributed to eastern part of the map. The yellow areas are the area where the pressure its quite high but slightly above the normal. We can say that pressure is not a variable that controlled by depth only (Fig 23), because in the southwest part of the area, we can see that depth contour does not align with the pressure grid.
The evidence of this overpressure can be observed from all pressure plots from all wells. From those pressure plots, there are points indicating the top overpressure because its exceed the hydrostatic pressure, but for determining the top, we use J-Wells as a reference point. 56
Interval 2 :
Figure 5.3. Pressure map for the second interval with the velocity contour
Figure 5.4. Pressure map for the second interval with depth contour
The mid depth for this interval is 1593 m, with Paciran horizon as the top of interval and bo1 horizon as the bottom.
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In the second interval, the overpressure zone is less distributed compare to the first interval. The overpressure ranges from 2830 psi to 5393 psi and the threshold velocity is 2090 m/. The overpressure areas are concentrated on the southern part of the map (Fig 24). It is quite safe to drill in most of the area here, because it was dominated by the normal pressure area (the blue areas). The most overpressure area concentrated in the north-east part of the area. Figure 25 is a strong evidence that pressure is a variable that are not controlled by depth only. The overpressure areas (the orange zones) are not align with the depth grid.
From the pressure plot, we can not see the top of overpressure for the second interval. we can only predict the top of first interval, because its exceed the hydrostatic all the way down. Paciran was picked and assumed as the top of second interval in order to calculate the interval velocity for the second interval, and bo1 was picked based on their strong reflector. The horizons are needed as a boundary when calculating the velocity interval.
Interval 3:
Figure 5.5. Pressure map for the third interval with the velocity contour
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Figure 5.6. Pressure map for the third interval with the depth contour The mid depth for this interval is 2627.3 m, with bo1 horizon as the top of interval and mundu horizon as the bottom.
In the third interval, the overpressure area becomes wider and concentrated in southern part of the map. It ranges from 4248 psi to 7710 psi. The threshold velocity is 2220 m/s. The distribution of overpressure areas are completely different with the previous interval. The overpressure area in this interval is a high degree overpressure (orange zone). The high degree overpressure can be seen in D-Well, J – Well and K-Well. The overpressure in AUWell and A3 Well has a lower degree of overpressure than the deep wells. The overpressure in this area might be caused by rapid sedimentation and/or uplift due to compression.
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Interval 4.
Figure 5.7. Pressure map for the fourth interval with the velocity contour
Figure 5.8. Pressure map for the fourth interval with the depth contour
The mid depth for this interval is 3491.3 m, with mundu horizon as the top of interval and to2 horizon as the bottom.
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For the fourth interval, the overpressure becomes widely distributed than the third interval. The overpressure ranges from 8240 psi to 12603 psi, with the threshold velocity 2280 m/s. The orange zones indicating high degree overpressure concentrated on the southern part of the map (Fig 28), while the blue zones indicating normal pressure zones are randomly distributed in all area, concentrating on northern part.
The calculation of interval velocity using Dix equation for this interval, might not be accurate due to the difference of the thickness laterally, the layer is so thin in the north west part (around AU-wells and A3-wells) and become thicker around the deep wells.
Interval 5:
Figure 5.9. Pressure map for the fifth interval with the velocity contour
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Figure 5.10 Pressure map for the fifth interval with the depth contour The mid depth for this interval is 3963 m, with to2 horizon as the top of interval and op2 horizon as the bottom.
The fifth interval is almost covered with the overpressure zone (Fig 30). The blue area indicating normal pressure zones are only seen in the center of the map. The overpressure are becomes even wider for this interval. The pressure ranges from 7290 psi to 14271 psi, with the threshold velocity 2300 m/s.
The high degree overpressure area concentrated in the middle to southern part of the map. The northern part area of the map is dominated with low degree overpressure.
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Interval 6
Figure 5.11. Pressure map for the sixth interval with the velocity contour
Figure 5.12. Pressure map for the sixth interval with the depth contour The mid depth for this interval is 4433 m, with op2 horizon as the top of interval and bo2 horizon as the bottom. 63
For the sixth interval, the overpressure zone becomes less distributed. The normal pressure zones become widely concentrate on northern part of the map. The pressure ranges from 8610 psi to 15536 psi.
The calculation of interval velocity in this interval might be not accurate due to layer thickness. It becomes thinner in the deep wells. The cause of overpressure in this area might be caused by the overburden from all the layer above it and high rapid sedimentation.
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