During horizontal drilling operations in the Daanzhai Formation onshore China, Shell lost its first well to wellbore stability issues that resulted in an LIH incident. Its second well—sidetracked from the first—was also lost because of poor borehole stability experienced during the completion stage. The wells' lateral sections in the interbedded formation were drilled to less than 500 m [1,640 ft] each before being terminated.
It was determined that the push-the-bit rotary steerable system (RSS) had failed to deliver the planned DLS of 3° in the first well because of breakout within the formation. Multiple stuck pipe events were recorded while drilling at a 15° azimuth and the borehole collapsed, despite the high mud weight (17 lbm/galUS) used to balance high formation pressure. Throughout the short-lived drilling phase using a push-the-bit RSS, the first well also experienced slow ROP.
Shell recognized that it would require a new approach when drilling its third horizontal well in the formation. SLB suggested running point-the-bit PowerDrive Xceed™ ruggedized RSS to help achieve the planned DLS in the breakout interval. Additionally, a different lateral orientation and casing seat design were proposed, discussed, and adopted. For this well, the lateral section azimuth was changed to 145° and the intermediate casing set deeper to isolate the troubled upper zone.
Working closely with Shell's well engineering and subsurface teams and using drilling data from offset wells, the SLB drilling engineering team implemented a prejob well engineering plan. Additional expertise in geomechanics was provided by SLB personnel in the local engineering center. During the drilling execution phase, a remote operations workflow was used to connect SLB personnel from across the organization to share knowledge in support of the ongoing operation.
Closely integrated teams of SLB drilling engineers and geomechanics experts collaborated with Shell experts to overcome the technical challenges preventing past success. SLB was involved in the directional drilling of the most challenging 9 1/2-in and 6 1/2-in sections over a drilling cycle of 19.1 d, including a break for casing. The total footage drilled in these two sections was 1,854 m [6,083 ft] with zero NPT.
The subject well was drilled in 24.2 d with a total footage of 3,667 m [12,031 ft]. In contrast, the best offset well in the block took 50.8 d to drill and reached only 3,491 m [11,453 ft]. This 52% reduction in drilling time was coupled with a DLS of more than 3.5°, which surpassed the targeted DLS of 2.5°. Based on cost-per-meter, the well ranks in Shell's top quartile and is considered best in class by the operator.
