corrosion in 7 inch scab liner
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27.06.2018

Reservoir flow analysis. SRO PLT in combination with spectral noise logging

reservoir flow analysis, spectral noise logging, SNL, noise log in SRO

The reservoir flow analysis survey was conducted in a subsurface water injector equipped with ESP producing water from lower perforations and injecting into the upper formation zone via two SSDs.

The main objective of PLT+SNL in this well was

  • to calculate ESP production rate
  • to evaluate water distribution between SSDs
  • to identify inflow intervals across perforated zone
  • to identify possible cross flow

The survey was conducted under two conditions: with ESP switched on and after ESP was switched off to evaluate the possibility of a natural flow.

Three down/up passes were conducted at an interval 2390-2490 mbdf at three different speeds, 5 m/min, 10 m/min, 15 m/min. Afterwards, spectral noise log under injection condition was carried out with a goal to determine the flow dynamics behind SSDs. Processed flowmeter data indicates a distinct distribution profile across SSDs with ESP production rate of 114.2 m3/d.  Produced water split between SSDs is as follows:

Upper SSD -35 m3/d (30.6%)

Lower SSD -78.2 m3/d (68.5%)

Up flow above upper SSD – 0.9%

SNL, reservoir flow analysis, PLT under injection

Temperature readings indicate that temperature of produced water is 101.7 degC. The profile of temperature curves is consistent with flowmeter data, i.e. curves sharply have changed gradient at a depth of 2416.7 mbdf at the top of upper SSD indicating end of intake zones.

Recorded SNL data under dynamic condition at interval 2390-2490 mbdf support PLT result and contributes to the understanding of water penetration zones across the perforated interval. High amplitude noise at low-frequency spectrum below SSDs is associated with upward water flow.

High amplitude noise identified at low frequency range of acoustic spectrum in interval 2390-2422 mbdf is associated to produced water turbulent flow. Two distinct spots detected in the medium frequency range of acoustic spectrum are related to water intake zones into formation. The color intensity of individual areas reveal difference in water distribution rate.  It is obvious that interval 2420.5-2422.1 accepts a higher amount of water that an interval 2416.4-2417.8 mbdf.

Noise amplitude at low-frequency range (0-5 kHz) at an interval 2380-2416 mbdf linked to upward flow which was detected by flowmeter.

SNL log, spectral noise log, reservoir flow analysis

SNL under Shut-in condition

SNL data was recorded immediately after ESP has been turned off. SNL was recorded stationary at an interval 2390-2490 mbdf every 1 meter. The result of shut in SNL differs from dynamic SNL and appears as a single spot located in the medium frequency range of the acoustic spectrum. This signifies that water enters in interval 2420.5-2422.1 mbdf. There is no indication of downward/upward crossflow behind the casing across the logging interval.

SNL, noise logging, PLT

PLT under Shut in condition

Shut-in PLT survey was conducted 2 hours after ESP has been switched off at an interval 2390-2490 mbdf after SNL pass. Flowmeter data revealed the apparent natural water flow in the range of 37.7 m3/d that enters lower SSD. This suggests that reservoir pressure in the formation is sufficient for natural flow even without the artificial lift.

PLT in injector, injection passes, spectral noise logging

Survey Conclusion

The result of this investigation shows that a combination of conventional PLT and SNL provide wider information necessary for evaluation of flow dynamics. PLT data allows to provide ESP production rate in the range of 114.4 m3/d and quantify the water distribution split between upper SSD (31.7%) and lower SSD (67%). SNL added value in terms of understanding of water penetration zones into the formation. Important conclusion drawn from the shut-in survey is that the well can act as free flow producer  (around 40 m3/d)  when the pressure at ESP discharge will be in the range of 27000 KPa. In contrast to artificial lift (dynamic survey), under shut-in condition all water flow enters lower SSD only.