- Oil channeling behind casing to surface—When annulus pressure rises and oil appears at the surface during bleed-off, the culprit may be fractured cement or other casing leak.
- Leaking packer—Excess annulus pressure may be caused by a leaking packer. The SNL log can detect high-amplitude broadband noise, which is indicative of gas flow through a leaking packer.
- Tubing or sliding side door leak—Increasing pressure in the annulus that equals tubing pressure suggests communication between the two, which can result from inflow through an unintentional open sliding side door or a tubing joint leak.
The log example below illustrates the detection of a production casing leak in an oil-producing well. The survey objective was to identify the cause of oil appearance at the surface and excess pressure in the A annulus. This was achieved by implementing the integrated HPT-SNL technique in two modes—under shut-in conditions and during pressure bleed-off from the A annulus. Shut-in spectral noise logging data revealed no fluid flow noise (see the shut-in SNL column), and the static temperature curve indicated no anomalies, qualifying both as baseline profiles. The SNL detected intense broadband noise during pressure bleed-off from the A annulus, shown in the SNL bleed-off column. Bleed-off temperature data, shown as the blue curve in the temperature column, displayed a heating anomaly created by choke effect during fluid entry into the A annulus at the dashed line. Above that depth, the temperature curves recorded in the two well states deviate. Broadband noise detected at the dashed line is indicative of turbulent fluid flow through a hole. A combined analysis of data recorded at that level indicated a casing leak. Low-frequency noise above the dashed line was caused by fluid flow through the A annulus.