Schlumberger

Case Study: Proactive Injection Monitoring Mitigates Risks for CRI Project

Protecting an environmentally sensitive area

Challenge: Increase surface injection pressure to mitigate premature suspension of injection operations for a cuttings reinjection (CRI) well.

Solution: Analyze subsurface assurance workflow and fracturing pressure response as well as proactively monitor injection to facilitate the timely planning of well workover operations to maintain the injection pressure to the minimum original level.

Result:

  • Reinjected a total volume of waste of more than 200,000 m3 [656,168 ft3].
  • Decreased friction losses and surface injection pressure to the original levels.

The Western Siberia oil field is located in an environmentally sensitive area that falls under strict state standards for drilling waste disposal. The dedicated injection well presented CRI challenges because the rathole length below perforations was only 5.6 m (18 ft). The recommended length for a rathole could not be less than 25 m [82 ft]. This did not meet the CRI well safety criteria because of the risk of solids accumulation across the perforation and subsequent perforation plugging.

Identifying the best solution

M-I SWACO, a Schlumberger company, started operations on the well by monitoring drilling waste injection performance. Identifying potential problems during subsurface injection provided additional understanding of injection domain performance and increased the overall assurance process. A detailed fracturing analysis of the injection pressure indicated that the pressure growth was driven by the friction losses inside the injection well; friction losses continuously increased with time and volume injected.

Implementing a logical solution

The recommended solution was to tag the current depth of the well bottom. Well bottom was tagged at 1,844.5 m [6,052 ft]. This meant that only 3 m [10 ft] of the 18.5 m [61 ft] of perforations were open for injection. After a well workover, M-I SWACO analyzed the injection and decline pressure, with results indicating the friction losses reduced to almost the original value. A reduction in the surface injection pressure increased the pressure safety window. The CRI well returned to normal performance, ensuring a seamless injection process. A total volume of waste totaling more than 200,000 m3 [656,168 ft3] was reinjected.


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