| Popis: |
Directional drilling control in top-hole sections through very weak shallow sediments is challenging. The formation tends to wash out, reducing steering control. The lack of reliable steering results in well kick-off-points planned deeper than optimal, especially for extended-reach wells or under multi-well platforms where early well separation is advantageous. Additionally, when drilling in close proximity to existing wells, well collision risk increases. As a result of these challenges, a major operator and international service company have developed, and proven, a hybrid drilling technique enabling reliable steering control in sediments which previously proved difficult to directionally drill through. The technique employs an automated rotary steerable system (RSS) and gyro-while-drilling tool operating in a directional jetting mode without rotation. The wells are drilled from an offshore platform through dual conductors. In addition to the well collision risks normally associated with multi-slot platforms, dual conductors mean that the second well drilled from each conductor is initially in very close proximity to the first well. Until this technique was developed, the top-hole sections were drilled with steerable motors because RSS were unable to steer consistently in the very weak shallow sediments. When the collision risk was passed, and the formations became firm enough for the RSS to operate, the steerable motor bottom hole assembly (BHA) was replaced with the RSS. The hybrid RSS jetting technique provides several advantages; a single BHA run can drill to section TD, shallower kick-offs are possible and predictable steering control reduces the risk of collision. The lower energy of the non-rotating jetting system is also believed to reduce damage to an offset well in the event of collision. The paper explains how the hybrid system was developed, and describes how it is applied and optimised in practice with real examples. Opportunities for further research are presented which may enable offset wells to remain on production, saving significant production loss and avoiding risk associated with well shut-in and start-up. |
