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Case study
Advanced acoustic analysis reveals complex fluid movement in the wellbore and close by the reservoir
True Flow Products Resource ID: CS007

Challenge

As part of a wider programme to enhance oil recovery, an operator of an offshore Abu Dhabi field wanted to obtain a more detailed understanding of fluid movement in and around their producer wells and identify the source of unwanted water. The diagnostic results would provide insights to support future decisions about reservoir management, remedial work and optimum workovers, and would shape the plans for drilling new wells.

Total-Flow-well-sketch
Total Flow locates and quantifies wellbore flow and – critically – reservoir flow to reveal the dynamic interplay between both.

Solution

The Total Flow product was selected by the client to understand wellbore and reservoir flows, and to manage the performance of the well system more effectively. Total Flow is delivered by TGT’s True Flow system which uses the Chorus acoustic platform and the Cascade thermal platform.

CS007-Total-Flow-Logplot
The channelling was detected by combining spinner, Chorus and Cascade results. The display on the CHORUS SPECTRUM shows the ‘spectral signature’ of amplitude (volume) and frequency (pitch) of the acoustic energy detected at various depths in the well; red regions represent high amplitude. Flow through the perforations creates low-frequency acoustic signal; the markedly higher-frequency energy is attributed to flow within the reservoir rock. The production profile built from spinner and multiphase sensor data is presented in the left two columns. The reservoir-related reservoir flow profile based on Chorus and Cascade Platforms data is shown in the right two columns.

Result

Spinner data showed that fluid (oil and water) inflow to the wellbore occurred only from the middle-perforated interval P2 across the A2 unit and that no fluid was being produced from either the upper or the lower perforation intervals.

 

High-amplitude and low-frequency (0.1 kHz) acoustic signal recorded in the middle perforated interval P2 indicated flow through the perforations. No low-frequency signals were recorded in the upper perforated intervals P1 and P3.

 

A high-amplitude acoustic signal at the top of A1 unit correlated with the lithology model, this suggested that fluid was moving through the reservoir matrix and that the top of the unit was producing (See logplot). Reservoir flow profile indicates this zone to be the main contributing interval in the target reservoir. Minor activity is captured across bottom part of A1 producing through the perforation interval P2.

 

A low-frequency signal extending down to the oil-water contact suggested a crossflow from the aquifer zone into the perforated interval P2.

 

Combining the data, the scenario assumes that the water was entering the wellbore, not from the target reservoir, but from the aquifer via a channel in cement. The scale deposition captured by the Gamma Ray tool across the entire interval where the low-frequency acoustic signal was observed supports this scenario. Additionally, the aquifer yield estimated by the Cascade platform correlated well with the water cut of this producer.

 

To increase oil production from this well it was recommended to 1) shut-off water from the aquifer, 2) re-perforate the upper perforation interval and 3) stimulate the lower one.