High-Thixotropy Lost Circulation Control Cement Slurry Technology for the Rumaila Oilfield in Iraq

To address the severe lost circulation in fracture- and vug-developed formations of the Rumaila Oilfield in Iraq, where conventional lost circulation control cement slurries are difficult to form effective plugs, a fully dry-blended low-density, low-strength thixotropic cement slurry system with a density of 1.30 g/cm³ was developed based on thixotropic mechanism analysis. This was achieved through the selection of thixotropic agents, optimization of lightweight materials, and regulation of early strength performance. Thixotropy evaluation methods were established using the static shear stress difference method and the consistency increment method to study the effects of a biopolymer thixotropic agent on the rheological and thixotropic properties of the cement slurry. The results show that with 0.1% biopolymer BDJ as the thixotropic agent, the low-density cement slurry system exhibits excellent thixotropic performance: a 30 min consistency increment of 39 Bc and a 30 min gel strength of 170 Pa. The setting time of the thixotropic cement slurry system is shortened to 5.0 h, and the 24 h compressive strength reaches 5.3 MPa, achieving the dual goals of “saving plugging time and preventing the drilling of new boreholes.” Compared with similar domestic and international technologies, this system demonstrates significant advantages in density, thixotropy, and early strength. Field test validation shows that the non-productive time for plugging operations is reduced by more than 30% compared to wells in the same block of the Rumaila Oilfield, providing a new technical solution for lost circulation control in low-pressure and easily lost-circulation formations.