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Abstract
Recent technological advances are driving casing 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. In Cooper Basin, onshore Australia the need to further reduce drilling expenses in area continues to push the technology forward.

At the outset of the project, the operator’s main goal was to improve drilling efficiencies with the aim of drilling more wells per rig per year. The secondary objective was to reduce costs and make the wells more economically feasible. To address these challenges, the service company recommended a specialized casing bit manufactured from a specialized steel alloy that allows technicians to braze 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 while drilling casing in place. They also recommended a new-style drill out PDC to drill through the casing bit and
continue drilling formation without tripping for a new bit.

The new 6-3/4” drill out PDC bit (XDO) was run with outstanding results. It demonstrated the ability to drill through the casing drilling shoe and drilled ahead 6,000ft to TD in one run. The XDO held inclination at high WOB and did not ball up. The successful trail proves the feasibility of this technology in a full scale casing drilling application, moving the application one step closer to reality. The bit company plans to redesign the XDO to improve performance in the drill out and through the softer formations out of the shoe.

The authors will make cost comparisons with offset wells drilled with conventional drilling systems. They will also focus on lessons learned through using this new technology.

Introduction
Onshore drilling in the Cooper Basin has been ongoing for the past 47 years (Innamincka 1 drilled in 1959). Several operators drill a combination of oil and gas wells in this area. Santos (the operator) by comparison drills a majority of the wells, with its production facility centered in Moomba, South Australia. Historically, the operator drills on average 50 gas wells (TD 10,000ft) and 40 oil wells (TD 6,500ft) per year. The wells are of a two string casing design taking up to 15 days to complete the gas wells (oil wells may take up to four days), with an extensive evaluation program (Figure 1).

Looking forward, the target was to drill approx 200 oil and 50 gas wells annually. These would be infill drilling in existing fields. Evaluation would be kept to a minimum. For their future campaigns, the operator had identified several areas for performance improvements:

• Improved environmental and safety performance
  
• Reduction in flat time
  
• Lower total well costs
  
• Increased wells drilled per year

To achieve these results, the operator required a step change in performance. They believed this was possible by moving towards fully automated drilling rigs. This opened the door for the evaluation of associated technologies such as Casing Drilling.1-8 It was deemed critical for the success of the shallow oil wells to reduce the flat time as this constituted a significant portion of the overall time spent on each well (Figure 2)

Objectives
As a result of this long range plan, the operator embarked on a process to prove their ability to casing drill in the Cooper Basin. The goal was to identify:

• Equipment requirements (and ensure long lead time items were ordered accordingly)
  
• Drilling parameters
  
• “Real” flat time reduction

The operator and service company’s engineering teams, working together as technology partners, broke the task into two clearly defined sections a) 9-7/8” casing drilling of the surface hole and b) 6-3/4” production hole drilling with 4-1/2” liner.