Preparation of a Drilling Fluid Degradable Cuttings Carrying Agent and Its Test in 10,000-Meter Deep Wells

In highly deviated wells, horizontal wells or large diameter wells, drilled cuttings are likely to accumulate on the lower side or at the bottom of the well due to insufficient cuttings carrying capacity of the drilling fluid. This will lead to complex downhole situations such as an increase in the friction of the drill string movement, difficulties in tripping, downhole lost circulation and even pipe sticking. Hole cleaning is therefore one of the key technologies to achieve operation safety and efficiency in highly deviated wells, horizontal wells or large diameter wells. A fiber cuttings-carrying agent that can significantly improve the cuttings carrying capacity of a drilling fluid was developed by blending and reacting an aliphatic polyester polymer with a high molecular weight copolymer. Results of performance evaluation experiments show that in the experimental slurry with 0.2% of the cuttings-carrying agent, the settling time of the cuttings increases from the original 4.12 sec to 19.85 sec. This cuttings-carrying agent has good dispersibility in both aqueous phase and oil phase. After hot rolling at 120℃ for 16 h, the degradation rates in clean water and white oil are 95.48% and 89.87% respectively, and the degradation does not affect the performance of the drilling fluid. Field tests show that this cuttings-carrying technology can significantly improve the cuttings-carrying capacity of the drilling fluid, effectively carry drilled cuttings or sloughing rock pieces out of large diameter wells or horizontal well sections, improve the wellbore cleanliness, and provide a guarantee for safe and efficient drilling.