Ultra-high Temperature Resistant Cement Slurry and Its Application in Hot Dry Rock

It is easy to cause the strength retrogression of cement sheath, especially at the long-term high temperature condition of dry hot rock. At present, the method of adding sand to strengthen cement is widely used in high temperature cementing operations. However, the strength retrogression of cement still exists when the temperature is above 200 ℃, resulting in casing collapse and annular flow, which seriously affects the wellbore safety. To solve the problem of cement strength retrogression at the ultra-high temperature, a new high-temperature stabilizer (SCKL) was developed by optimizing the phase composition of cement based on the enhanced effect of silica aluminum bonding. The effect of SCKL on the inhibition of set cement strength retrogression at high temperatures was evaluated. The results showed that the compressive strength of set cement was 18.2 MPa at 48-hour age for 300 ℃ curing temperature. And the strength reached 23.2 MPa after 30 days, which inhibited the strength retrogression of cement under long-term high temperature conditions. The influence of temperature on the microstructure and hydrates of set cement was revealed based on the XRD and SEM tests. Finally, a new durable heat-resistant cement system was developed. The cement slurry had very good settlement stability and could meet the requirement of safe cementing in DHR wells at a temperature difference of 100 ℃. The durable heat-resistant cement system has been successfully applied in five wells in Gonghe Basin, Qinghai Province. The cementing qualities are very good, which provides a guarantee for the integrity of cement sheath sealing in dry hot rock.