Achieving successful isolation of potential flow zones during well construction from floating rigs has historically been a formidable task, particularly on HPHT prospects. Operational challenges include actual vs. predicted leak-off test (LOT) values, margins of error in mud weights, high temperature compressibility at shoe depth and risk of inducing a fracture during pre-flush and/or cement slurry displacement. Wellbore strengthening operations may contribute to the relative unknown. Additionally, it is often assumed that the weakest component of the cementing operation is the last casing shoe, which may not be the case.
This presentation speaks to conducting dynamic formation integrity tests when drilling the open hole to be cased and cemented and applying managed pressure drilling (MPD) techniques as a means of increasing chances of getting a good cement job on the first attempt and in keeping with the intent of API Recommended Practice 65, Part 2- Isolating potential flow zones during well construction:
Preparatory - quantify the stability of the wellbore, actual wellbore pressures data for correlation with cementing simulator models & more efficient hole cleaning ahead of the cement.
Displacement - optimize fluid dynamics, ascertain in real-time an induced fracture and/or help ensure the column of plug in the tubing string is balanced with the annulus.
Curing -maintain more consistent annulus pressure on rigs experiencing wave heave & backpressure applications for minimizing the risk of channeling.
Testing – using MPD kit in lieu of cementing equipment or exercising the BOP.