Shell China, in partnership with PetroChina Southwest began horizontal completions in its Sichuan shale gas project in 2012. By the end of 2012, two vertical and three horizontal wells were drilled and completed in the Lower Longmaxi Hot Shale interval. Performance has continuously improved throughout the implementation of the completions program1 and significant technical and operational challenges were overcome.
The three horizontal wells were drilled with progressive horizontal lengths. On the third and longest well in the sequence, difficulties were encountered when attempting to mill plugs in the horizontal section. Well pressures were in excess of coiled tubing limits and the plugs could not be milled. As a result, the well was produced with flow-through plugs in place until the well pressure could be reduced and a higher pressure coiled tubing reel was available. Due to the high well pressures observed, additional measures were taken to reduce operational risk during the coiled tubing millout and ensure a successful operation. The flowback package design was improved by utilizing hydraulic chokes in place of manual chokes and a dual-plug catcher system was installed in the flowback package. In addition to improving the flowback package for millout operations changes were made to the flare system. After the coiled tubing millout was completed, difficulties were encountered during the full phase well test requiring the horizontal flare to be replaced with a vertical flare due to HSE concerns. The challenges experienced during this operation and the improvement aspects gained will be utilized in the completions planning and execution of the next phase of horizontal wells.
This paper highlights the coil tubing millout, flowback, and well test learning experiences gained during the completion operations of the second and third horizontal wells.