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Victoria University Antarctic Research Expedition Science and Logistics Reports 1998-99: VUWAE 43

Cementing

Cementing.

The initial cementing operations were not successful. Previous cementing in CIROS- 1 and page break CRP-1 appeared to work satisfactorily, but none of this cement had been cored to confirm that cementing techniques and setting times were appropriate. Expert advice and cementing references had suggested that we would need to use high concentrations of Calcium Chloride accelerator in the cement for low temperatures. However, our situation was more complex than the "textbook examples" because we are also using sea water containing Sodium Chloride which is also an accelerator. We also knew that high concentrations of both accelerators can react as a retardant and or weaken the cement

At the time of the first cementing attempt for CRP-2 we therefore had not been able to confirm that the theoretical cementing techniques and previous cementing attempts were working properly at sea floor temperatures of −1.8 degrees Celsius. Placement of the cement was carried out with proprietary cementing plugs directly within the riser for the first two cementing attempts. We hoped these plugs would speed up the operation but the plugs were unsatisfactorily in the modified riser string. The third cementing of the sea riser at about 13 m bsf appeared to work, although we could not positively confirm this by recovering strong cement core.

The cementing of the HQ drill barrel at 199.31 m, where down-hole temperatures were theoretically +5 degrees Celsius worked well, with several metres of hard cement recovered. This confirmed that the cement/accelerator mix was appropriateand indicated maximum setting times. A long setting time was deliberately allowed for this primarily because it was vital that the HQ barrel landing ring and diamond coring bit were locked firmly in place to be successfully drilled through with the NQ drill string. Major delays could have occurred or even hole abandonment if drilling out of the barrel was not successful. However, even with this latest CRP-2 experience we still do not have positive confirmation of the setting times required for initial cementing at the sea floor at −1.8 degrees Celsius.