TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOperators are always looking for ways to reduce risk in high cost environments and maximize value. Many challenges exist in the drilling environment today including depleted sands, lost circulation zones, weak formations and rubble zones. Casing and liner drilling has found its way from a niche market into the mainstream drilling environment through recent successes in a variety of these applications. There exist several options to drilling down casing or liners. These include retrievable BHA's with traditional measurement and logging equipment and non-retrievable BHA's that are drilled or reamed into place and cemented. This paper presents several case studies where non-retrievable casing/liner drilling technology has either improved the economics of a challenging application or made the application technically viable. These applications vary from onshore wells with tight fracture gradient schemes, shallow onshore wells looking to improve economics in surface hole intervals to offshore wells reducing risk by drilling or reaming down casing and liner strings. Applications will be taken from the Gulf of Mexico, South Texas, West Africa, Australia and Norway. The justification of using casing/liner drilling technology on these wells will be explored, as well as the lessons learned to apply to future drilling programs.

Recent technological advances are driving casing and liner drilling from a niche market into the mainstream environment. Improved connections, tubulars, advances in rig technology and pipe handling have enabled operators to consider drilling with casing/liner as an option on many new wells 1,2 . Escalating deepwater costs and the need to further reduce onshore drilling expenses in low cost fields continue to push the technology forward.In a mature South Texas field, an operator discovered the difficulties of drilling into formations with weak matrix strengths, loss circulation zones, and tight pore pressure/fracture gradient windows.These issues have deemed the field sensitive to aggressive drilling techniques and the operator has been forced into a conservative drilling program with reduced flow rates and lower weight-on-bit capacity. The operator needed to reduce trouble time, lower costs and make the wells more economically feasible.A service company introduced a new liner drilling system solution to get through the extensive problematic zones. The system is engineered so the operator can ream to bottom and then continue drilling with the liner to the required target depth. The system is comprised of a drillable fixed cutter casing bit and a drill-in liner assembly designed to handle the rigors of a drilling environment (rotation, reciprocation and drilling torque). The liner system utilizes a running tool that allows the liner to be used in drilling mode handling all the required drilling loads without fear of release. Once at desired setting depth, the hydraulically balanced liner-running tool is released with a setting ball. The casing bit is manufactured from a specialized steel alloy that allows technicians to braze polycrystalline diamond compact (PDC) cutters directly to the one-piece bit ensuring a robust cutting structure capable of efficiently drilling new formation as well as reaming existing hole. The system allowed the operator to drill in the liner to TD, cement, and then drill out to the next casing point.To date, nine intervals have been drilled with this system in South Texas. This paper will focus on the problems encountered in the field, the development work in establishing a solution for the operator, the results attained, and lessons learned through using this new technology. TX 75083-3836, U.S.A., fax 1.972.952.9435.

In 2015, the operator deployed a global initiative that focused on using physics-based principles to optimize various aspects of the well construction process. The initial rollout emphasized optimization of on-bottom drilling time utilizing mechanical specific energy (MSE), and this was successful in generating step changes in performance. The success of this initiative, and the internal and external marketing of that success, laid the foundation for the physics-based digital workflow developed in the operator's international business unit in Oman during the second quarter of 2017. The drilling teams launched a proof of concept in Oman in July 2017 to test the workflow. Throughout the proof of concept, the workflow was digitized, and it evolved into a robust web-based application to serve as the framework to facilitate consistent, repeatable, and scalable execution of the physics-based workflow. The purpose of this paper is to illustrate the benefits of utilizing a physics-based workflow as well as to describe the innovative approach the operator used to execute the physics-based workflow. The workflow overview, proof of concept results, challenges, and future opportunities are discussed in detail. During the proof of concept, which lasted from July 2017 through August 2018, field personnel from eleven drilling rigs submitted over 4,000 entries into the digital workflow application. Office-based personnel then launched 32 design projects, addressing more than 200 of the issues identified. Of those 32 projects, 17 were completed within the specified period. In one particular field, the drilling team achieved a 20% reduction in well cost and a 27% reduction in drilling days on location by using this digital workflow. Overall, both drilling teams in Oman experienced tremendous performance gains throughout the proof of concept, with one team achieving a 72% increase in footage drilled per day, and the other achieving as much as 32%. The success of the proof of concept led to the operator's decision to deploy this web-based application and digital workflow globally in the second half of 2018.