“Thermally accelerated cement displacement”. As the TACH process had mixed results and several un-intended consequences (which lead COP away from this process), we should not suggest it is a “silver bullet” solution, but one of several that can be considered for further investigation. My suggestion would expand processes that mitigate the influx of fluids during cement transition as follows:
• Process improvements that mitigate the influx of formation fluids during cement transition phases, which may include the following examples, with potential new applications;
o Thermally accelerated cement during cement transition;
o Use of silicates of other formation treatments that inhibit the influx of fluids into the formation/casing annulus;
o Cement fluid loss additives to mitigate cement shrinkage to the formation:
o Multiple cement blends and/or alternate “pancake” cementing techniques;
o Timed and variable rate cement placement based on slurry properties.
I disagree with the comment that implies excessive circulating rates and rotation of the drilling BHA creates wellbore cement slump integrity issues, with potential associated wellbore leakage issues. Rotary speed and circulating rates are key to hole cleaning and mud conditioning, providing improved wellbore quality for optimised cementing results. Successful elimination of cement slump (using hesitation displacement) on project wells did not involve a reduction of circulating rates or rotating speed while conditioning the hole for casing and cementing operations. While a gauge hole is desired over the entire well, a properly conditioned hole is key to an effective cement job and reduced well leakage.
The discussion regarding casing string reciprocation and rotation communicates the benefits of casing movement to an effective primary cement job. However, the illustrations from Kellingray (BP, 2007) modelling flow patterns when rotating do not capture the “viscous coupling” effects while rotating casing (for improved cement isolation) adequately. Viscous coupling is a boundary layer phenomena created by viscous surface layer effects, which effectively “draws” a layer of cement (or adjacent fluid) along the surface of the rotating casing (around the circumference) to the area of poor annular flow. Circumstances affect the contribution from viscous coupling, but in intervals of poor standoff, a mud channel may be mitigated. The higher the rotating speed and duration, the greater the contribution from viscous coupling to the mud displacement. Flow modelling shown in the figures included do not capture this viscous coupling effect, and someone unaware of this benefit may decide against rotation due to the other risks and requirements identified. The primary risk is connection fatigue failure; total rotations should be monitored and limited based on well design. Torque and Drag analysis is also recommended to evaluate torque requirements and limitations.
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