| Popis: |
In order to develop a giant mature carbonate field offshore Abu Dhabi, four environmental Islands were built in shallow water. Due to the large areal extension of the field, most wells are Extended Reach. This paper presents a case study of the longest well drilled in the UAE. Planning to drill such an Extended Reach well with maximum reservoir contact, starts long before execution. Not only, competent rigs, capable of delivering enough mechanical and hydraulic energy to drill such well, but also placing and navigating the lateral section in multilayered anticlinal reservoir with layer cake geometry. Significant geologic uncertainties of complicated carbonate facies heterogeneities is a major challenge. Detailed study of the reservoir behavior according to pre-existing nearby wells was carried out, as well as understanding the geologic structural setting of the area since the target zone consists of 5ft thick limestone layer that overlays a 3 ft. thick dolomitic limestone with excellent permeability. The crucial success factors were; firstly, to steer in such a thin reservoir for long distances, using LWD tools to differentiate dolomite from the nearby limestone layer. Secondly, to account for possible lateral facies change, the sensors needed to be as close as possible to the bit. Considering +28600 ft. horizontal section, remarkable challenges arose related to drilling tool capability and well path smoothness. The drilling team was concerned about using nuclear source density tools to navigate the well path and needed to avoid high dogleg to prevent any fishing jobs associated with source tools, especially in fractured areas. The well was drilled to record depth of more than 45300 ft. with a horizontal section of 27,500 ft. inside reservoir. Utilizing Rotary Steerable System in all hole sections helped to minimize hole tortuosity along the well and with the help of LWD tools the well was accurately steered within target zone boundaries. Utilizing advance mud telemetry made it possible to receive data from 45,300 ft. away from surface. Successful well placement was the main factor to achieve positive overall performance in the field. This success has opened the door to drill more wells that are more challenging. In addition, it practically proved that proper planning and execution can push the limits further and gave confidence to drill even deeper. As a result, we are now aiming to drill deeper wells up to 50,000 ft. |
