Managed Pressure Cementing Allowed Flexibility of Adjusting 3-Variables to Minimize the Losses Rate Instantly During Cementing Hence Assuring Well Integrity, A Case Study

Abstract

Both cement quality and quantity play a major role in well integrity. The quality of bonding between casing and cement can be maintained if no downhole fluid losses occur during the cementing operation. For quantity aspect, relying only on the total cement volume pumped will not guarantee that the planned cement height in annulus is achieved. During job execution an induced fracture might cause considerable cement column to be lost into the opened fracture-zone.

The reason for this higher bottomhole pressure are primarily due to the high rheology of the cement slurry and spacers and also the annular space between the casing assembly and bore hole is lesser as compared to the drilling assembly during drilling phase which generates higher annular friction pressure losses aiding to the high bottomhole pressure. In addition the density of the slurry and spacer is usually higher than the drilling fluid which also further increases the bottomhole pressure. All these three factors make the likelihood of lost circulation more than during the preceding drilling phase.

The case study highlights how these challenges were addressed during cementing. Initially by designing a lighter mud density used in combination of surface back pressure, SBP improving the density hierarchy of the cement to reduce the chances of contamination. Additionally utilizing the early kick/loss detection system to instantly detect and minimize the losses during the job execution.

After Managed Pressure Cementing simulations a lighter MPC mud, 123pcf was proposed which in combination with the SBP and pump-rates will provide flexible EMW adjustments if required. It was planned to adjust the cementing pump-rates to minimize the high bottomhole frictions during the operations as dictated by the loss rates. The cement hardening time was pre-adjusted accordingly by adding the necessary retardants.

Throughout the cementing operation, the well was monitored closely using the early kick/loss detection system and suggested to reduce the ECD first by reducing the SBP and then by reducing the pump-rates. Enabled flexible EMW adjustment by fine tuning either SBP or pump-rates real-time as dictated by the losses. The ECD was managed real-time and almost instantly. Total 15-18bbls only was lost during entire cementing ensuring proper well integrity.

Minimizing losses during cementing operations is imperative for achieving adequate zonal isolation. The most common well integrity issues involve fluid migration through leakage pathways. Also, the dynamic pressure and temperature conditions during drilling and production exert a cyclic load on cured cement, and sometimes initiates cracks in the cement. These cracks then have the potential to act as pathways for fluid migration. Therefore avoiding troubles during primary cementing is essential for assuring well integrity.