Abstract
An operator in offshore South China planned to develop a new oil field comprising multiple thin oil-bearing zones. It was decided to develop the field by upgrading an existing drilling rig on a platform rig 6 km away to drill extended reach horizontal wells. The objective was to place long lateral drains in a thin-pay reservoir. However, the foreseen risk of high drilling torque against the backdrop of the drilling rig that has maximum 42,000 ft-lbf drilling torque capacity limited this option. In addition, subsurface challenges constrained the ability to access the target reservoir optimally for production and reserve recovery optimization.
The latest fit for purpose logging-while-drilling applications were used to overcome the drilling challenges—limited rig capacity and subsurface challenges—in these extended reach horizontal wells and to optimize ultimate recovery and the economics of each additional well drilled. The efforts were performed in real time while drilling and aimed to place the well optimally within the thin pay zone by delineating and mapping the top and bottom pay zone boundaries simultaneously. With this ability, the lateral could be placed accurately without making unnecessary trajectory adjustment that can result in additional drilling torque.
Two wells were completed successfully. Application of the technology resulted in significantly higher production compared to the set target. The reserve recovery was optimized by placing the well 0.5 m below the top. The drilling torque was minimized, thus increasing the ability to drill farther and capture additional reserves. Significant savings in total drilling cost were attained by ensuring smooth drilling operations free from unnecessary adjustment and sidetracks. A similar approach could address the challenges in other, similar complex and hard to reach reservoirs targeted in exploration and development activities in offshore operations.
