Quantitative risk assessment technology for ultra-deep well drilling in the Homatu structural belt of the Junggar Basin

The Homatu Structural Belt in the Junggar Basin exhibits geological characteristics such as complex pressure systems and narrow safe density windows. Complex conditions frequently occur during construction operations, which severely restrict the safe and efficient implementation of ultra-deep well drilling. Results of traditional drilling engineering risk assessment are mostly qualitative or semi-quantitative, failing to meet the safety requirements for high-risk drilling operations in the Homatu Structural Belt of the Junggar Basin. This study establishes a set of quantitative risk assessment technology for ultra-deep well drilling. Firstly, the formation pressure with reliability is calculated, and the safe drilling fluid density window for the target well is established. On this basis, the quantitative risk assessment technology for ultra-deep well drilling is developed in accordance with the wellbore equilibrium criterion. Results of case analysis on ultra-deep exploratory wells in the Homatu Structural Belt of the Junggar Basin indicate that the drilling risks calculated by the proposed quantitative drilling risk assessment technology in this study are highly consistent with on-site actual conditions, which can provide guidance for the safe operation of ultra-deep well drilling in this area.