Improved method for selecting kick tolerance during deepwater drilling operations.

摘要

One of the most critical aspects in the design of oil and gas wells is the selection of the depths at which steel casing is set. As the length of open borehole increases, the risk of formation fracturing during drilling operations increases. Formation fracture often leads to an underground blowout that can be very expensive to control. Because of the special problems involved in drilling deepwater well, accurately measuring the risk of formation fracture is essential. A calculated parameter called "kick tolerance" is often used to measure this risk.; In this study, improved computer software specifically designed for computing kick tolerance for wells drilled in deep waters was developed. During well design, the software can be used to confirm previously calculated casing setting depths. The software can also be used during drilling to estimate the fracture risk of the weakest exposed formation if a kick was taken and circulated. If an unacceptable fracture risk is indicated, drilling can be interrupted and the casing string can be set earlier. The developed computer program has been proven to be fast, reliable, and suitable for available rig site computers. The accuracy achieved was similar to that obtained using commercially available well control simulators that are much more time consuming to run. The availability of this simulator may result in safer drilling operations and improved capability for drilling in deeper water depths.; Experiments were performed using a drilling fluid and natural gas in a 6,000 ft research well to verify and improve previously published empirical correlations for gas rise velocities. An empirical correlation relating the gas velocity to the sum of the average mixture velocity and the relative slip velocity was determined using both the available data from previous flow-loop experiments and data from the present experiments. This correlation was used in the new computer software. The experimental data may also allow additional improvement to be made in the accuracy of the kick tolerance calculation in the future. Investigation of a triangular gas distribution profile along the path of upward gas migration is proposed as a future area of study.