Innovative Modeling System Develops New PDC Bit Technology: Saves Operator 55% Drilling Time in First Deep Jurassic Slimhole Development Well, Kuwait

Al-Enezi, Dakhel (Kuwait Oil Company) | Al-Khaldy, Ali (Kuwait Oil Company) | Al-Mutawa, Faisal (Kuwait Oil Company) | Al-Mkhyal, Abdullah (Kuwait Oil Company) | Maliekkal, Harish (Smith Bits, a Schlumberger Company) | Ghoneim, Osama (Smith Bits, a Schlumberger Company) | Saleh, Mustafa (Smith Bits, a Schlumberger Company)


The North Kuwait Development Project requires a large-hole casing design to isolate problematic formations and enable the operator to reach deep HPHT target zones with maximum hole size. The most difficult section is Zubair to Hith traditionally drilled with 16?? bits. These formations consist of abrasive/pyritic sandstone, reactive shale and carbonates with UCS between 5-30kpsi. Historically, to complete the 3900ft section required more than three PDCs or a combination of 4-5 PDC/TCI.

To reduce costs, the first slimhole development well plan and string design was developed for Northern Kuwait fields. The objective would be to downsize the hole section from Zubair to Hith to 9¼?? and drill to section TD with three PDCs. The production casing would be run from surface to TD instead of the conventional liner tie-back.

To accomplish the objective, the team decided to develop two different 9¼?? PDCs: 1) one for Zubair to Ratawi shale; 2) a second for drilling the remaining carbonates from Ratawi to Hith. To avoid costly field trials, an FEA-based modeling system was used to fully understand how iterative bit design changes would affect performance and drilling efficiency. Based on modeling, two PDC bits were implemented: a M819 with back-up cutters to achieve maximum durability and ROP through Zubair and push deep into Ratawi; a M616 to drill the remaining section from Ratawi to Hith. The bits were equipped with the latest HTHP cutters to enhance durability/ROP.

The section was completed on a motor BHA in two bit runs saving 55% drilling time and the expense of a third bit. The operation set a new Kuwaiti record for the single longest 7¾?? production casing string (13,625ft) and cementing back to surface. The downsizing strategy and increased drilling efficiency saved the operator $1 million USD compared to project estimates and a standard liner-string design.