This paper presents an investigation into the sudden changes in water cut in oil producer wells and their impact on well integrity. The study proposes a comprehensive workflow supported by various case studies. Additionally, the research explores the salinity variation across different formations, the water samples acquired from various locations in the reservoirs, both aerially and vertically.
The workflow, while straightforward, proves crucial in preventing significant well integrity issues that could have been addressed at an early stage. It commences as soon as the well experiences a sudden increase in water cut. First, a water sample is collected for geochemical analysis and salinity estimation, cross-referenced with the reservoir's aquifer data. If the figures match, it indicates that the water source is the aquifer; however, discrepancies may indicate casing leaks or water flow behind the casing.
To confirm the external water source, a temperature log is conducted to detect abnormal temperature anomaly; i.e. cooling effect. If such anomaly is observed, a corrosion log is used to identify the casing leak depth in the well. Appropriate actions, such as cement squeeze, liner, scab liner or casing patching, are then undertaken. If no cooling effect is observed, USIT (ultrasonic Imaging tool) is used to asses the cement bond behind the casing. Additionally, a water flow log (WFL) is mandatory to confirm the presence of flow behind the casing, and a cement quality log is also obtained. A presence of a temperature anomaly suggests a hole puncture in the casing, while poor-quality cementing indicates flow behind the casing. Subsequently, remedial actions are implemented based on the obtained results. Adhering to this workflow enables an early resolution of potential well integrity issues, mitigating risks and ensuring smooth long-term operations.
An investigation of three cases yielded significant findings, particularly a distinct observation of a cooling effect and temperature increase in a non-producing well. Prior to conducting the temperature logs, water samples were collected from all wells, revealing lower salinity values compared to the aquifer salinity. Subsequently, the temperature log confirmed the presence of a casing hole, which was promptly patched.
In Case 1, the estimated salinity value was in the range of 100,000 ppm compared to the actual salinity of 170,000 ppm. The temperature log clearly indicated a notable increase in temperature along the wellbore, which is attributed to water influx from the shallow water-bearing zone during a shut-in period in the well's life. Case 2 also demonstrated a casing leak across a water-bearing zone, as the salinity dropped from 190,000 ppm to 97,000 ppm. Prompt remedial actions were taken to patch this casing hole. Regular temperature logging is now scheduled as a proactive measure in case of potential casing leaks. Various remedial actions are available, including water shut-off, cement squeeze, scab liners to seal leaking intervals, or running a smaller liner to seal the leaking zone. However, caution is required in selecting the appropriate method, as some options may reduce the well's ID and restrict production. In Case 3, a casing leak was also identified across a water-bearing zone, and a temperature anomaly was observed in the wellbore. The detection of this temperature anomaly provided a clear indication of potentially causing integrity issues in the area adjacent of the water-bearing zone. Upon further investigation, including the use of diagnostic techniques such as corrosion logging, the casing leak was confirmed.
In conclusion, a well-detailed workflow has been established, striking a balance between logging, water salinity measurements, and well monitoring to prevent any integrity issues and crossflows in the wells. This time-efficient methodology assists engineers in identifying the source of produced water and maintaining well health. The implementation of simple water shut-off techniques, casing remedial actions, and strategic production strategies effectively address water-related issues, safeguarding well integrity against water flow from casing leaks.
