ABSTRACT:

Cementing in the hot-dry rock formation faces high temperature (>150°C) at the bottomhole, large temperature difference (>50°C) along the sealing section, and frequent temperature and pressure fluctuations during the production, which seriously restrict the long-term integrity of the geothermal wellbores. Therefore, it is necessary to construct a new cement slurry system for dry hot-dry formation. Firstly, a strength stabilized material was developed through optimizing a high silicon- aluminum material mixed with silica powder. Secondly, a cement retarder adaptable to a wide range of temperature were generated. In addition, liquid silicon was added to improve the mechanical characteristic of set cement. On the basis of above measures, a new cement slurry system with high temperature resistance and high strength was formed. Experimental results show that the cement slurry with heat resistance of 205°C has good rheological and thickening properties, and the applicable temperature difference is over 100°C. The compressive strength of set cement was greater than 24 MP which had no recession in 30 days, and the Young’s modulus was as low as 6.5 GPa. Furthermore, the cement sheath maintained a good sealing performance under 30 alternating cyclic loading with the temperature (110~160°C) and pressure (0~50 MPa) conditions. The cement slurry system had been preliminarily applied in Tarim basin and expected to provide a reliable technical guarantee for the long-term development of geothermal wells.

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