Pressure-controlled cement plug injection technology with ultra-high-density cement slurry in well Hetan 1

The key risk exploratory Well Hetan 1 encountered oil-gas layers with ultra-high pressure during drilling in the fourth section, while the internal strength of the Ø244.5 mm casing in the second section is 60 MPa, which is insufficient to shut in the well, posing well control risks. In order to ensure the normal construction of cement plugback with Ø177.8 mm casing in this well, weighting materials and admixtures were screened through indoor experiments. A cement slurry system with a density of 2.60 g/cm³, suitable for cement plug injection construction in this well, was prepared by adding spherical iron powder as weighting material. Under conditions of 160 ℃ and 170 MPa, the strengths of the cement slurry system after 48 hours and 168 hours were 24.5 MPa and 28.1 MPa, respectively, with a filtration loss of 23 mL. On-site construction was carried out using the batch mixing and batch injecting method, combined with precise pressure control technology, achieving pressure balance throughout the cement plug injection construction process. The cement plug injection construction in this well was successfully completed, and the quality of the cement plug met the standards. The application results show that the cement slurry system with an ultra-high density of 2.60 g/cm³ is suitable for similar ultra-high-pressure cementing operations. And through precise pressure control, it can solve the pressure fluctuation issues when the drilling fluid density is insufficient to stabilize the formation and during cementing with narrow safe density window, which brings experience for subsequent pressure-controlled cement plug injection and pressure-controlled cementing in similar wells.