Laboratory Study on an HTHP Ultra-High Density Cement Slurry

The well Tianwan-1 is an ultra-deep exploration well located in the middle of the Junggar Basin, with depth of 7,500 m, bottom hole pressure of 170 MPa and bottom hole temperature of 160 ℃. A high temperature high pressure ultra-high density cement slurry was developed in laboratory to overcome the high temperature and high pressure, as well as the other problems related to ultrahigh density cement slurries, such as poor fluidity, poor settling stability, high dynamic fluid loss, and over-retarding of the strength of the top set cement under big temperature differences, etc. The highest density of the cement slurry was 2.55 g/cm³. The cement slurry was developed with a new weighting agent, micronized silica, a high temperature stabilizer, powdered silica passing through 600-mesh screen, a new micronized manganese powder, a suspending agent, a high temperature retarder, a high temperature filter loss reducer and a high temperature friction reducer. Laboratory experimental results showed that the cement slurry had fluidity of 32 cm, good settling stability, high strength of top set cement and strong capacity of anti-channeling. The thickening time of the cement slurry is linearly adjustable at 160 ℃ and 170 MPa. Dynamic filter loss of the cement slurry was 40 mL. The cement slurry can be used in a wide range of downhole conditions; by changing the concentrations of the different additives, the cement slurry can satisfy the needs of cementing operation at different downhole temperatures (hence different depths) in the well Tianwan-1.