At present, thermal recovery is an important method for developing heavy oil reservoirs effectively. However, the leakage of cement slurry into the formation during cementing and steam leakage through cement in the annular space around a cemented casing during production have become a problem to be urgently solved in heavy oil reservoir thermal recovery production.
The solutions to these problems are usage of two-stage cement slurry system and the dynamic vibration cementing. The well section from 100 metres above the top of oil layer to the wellhead is cemented by a novel foam cement slurry system, and the rest of the barefoot interval is cementedby the good thermal-stability cement slurry system by using the dynamic vibration cementing technique. The objective of usage of two-stagecement slurry system is to reduceannulus fluid column pressure, and the objective of the dynamic vibration cementing is to achieve a stable hydraulic seal.
The consequences of the pressure reduction in the cement columnare evident. Not only the difficulty of leakage in cementing is settled by applying the low-density foam cement slurry, of which the density is 1.40 g/cm3, but also the heat loss of wellbore is decreased because of reduction of thermal conductivity. The performance of thermal-stability hardened cement paste before and aftersteam vapor curing was compared by lab experiments. The result shows that the compression strength, tensile strength and shear stress of hardened cement paste and of hardened cement pastehad little change. SEM photographs indicate that the microstructure of hardening cement after vibration action is more compact.
These results had been validated on site test. Through the comparison and analysis of cementing quality of two wells in the same block, it has proved that the well with this novel cementing technique is better quality than the other one. The CBL/VDL test report revealed that acoustic amplitude value of the well is less than 10%. The formation wave of the well is clearer than the other and casing wave is weaker.
Through usage of two-stagecement slurry system, not only the difficulty of leak formation in cementing is settled, but also the wellbore heat loss have come down significantly during the course of thermodynamic oil exploitation. And the dynamic vibration cementing can achieve a good thermal-stability hydraulic seal in the annulus space.