Accurate casing and tubing integrity monitoring is essential to preventing failures and accidents. GR Energy Services offers TGT noise logging to monitor fluid flow behind the casing. Based on spectral noise logging and high-precision temperature, the combined HPT-SNL tool accurately identifies leaks in the casing or tubing.
The addition of spectral noise logging to the temperature measurement helps operators see a detailed description of leak locations and reservoir flow—an improvement over using temperature data alone. Analysis of temperature measurements to detect downhole leaks has been used for decades, but recent advances in temperature tool design allow for a much faster response (less than 1 sec) and much better resolution (0.003°C).
Many wells experience the following integrity problems which can be detected by temperature and noise logs:
- Casing leaks in injection wells can result in undesired fluid injection, while leaks in completion components of production wells often decrease production rates and increase water cut.
- Leaks in casing, tubing and packers can increase annulus pressure, putting well operations at risk.
- Casing leaks result in crossflows behind casing, which can lead to unpredictable reservoir performance.
Fluid flow through tubular leaks generates a noise pattern that is different from noise generated by fluid flow through the reservoir. Spectral noise logging can distinguish between both types of fluid flow, making it ideal for leak detection. Leaks through cement can be traced by their characteristic signature responses.
The HPT-SNL leak detection method is a two-stage process. In the first stage, temperature and noise are recorded under shut-in conditions as baseline measurements. In the second stage, temperature and spectral noise surveys are conducted while bleeding off fluid from the problematic annulus. Excess pressure bleed-off causes some extra fluid to enter the annulus, which is detected by the temperature and noise logs.
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.
Oil flow through a casing leak causing heating and wide-range noise. Above the leak point, low-frequency noise indicated oil flow in the A annulus.