China’s Sichuan Basin contains prolific gas fields and presents many drilling challenges due to the complex structural geology. Xujiahe is one of the most challenging formations in the basin. The interbedded and hard, abrasive nature of Xujiahe results in short intervals drilled and low rates of penetration (ROP).

Polycrystalline Diamond Compact (PDC) bits have limited drilling efficiency in this formation because impact damage and abrasive wear lead to short intervals drilled and very low ROP. Seven-bladed PDC bits which replaced roller cones were once believed to be the most cost-effective solution. To expedite gas exploration, improve ROP and increase distance drilled in the Gaoshiti-Moxi block, an innovative application-specific engineering drill bit was required.

To identify the solution, a cross-functional team from the drilling contractor and the service company conducted extensive technical research into drilling practices. Sophisticated software was used to analyze the rock properties, and to identify the formation drilling problems. Reviews of offset drill bits provided clues to drilling challenges. After a series of technical analyses, an application-specific hybrid bit was designed and tested in this block. Continuous optimization of drilling parameters is implemented by field engineer.

The first three trials drilled through this formation, saving two PDC bits and two trips over a 500-meter interval. Post-run review and analysis of the first trials was conducted for further improvement of ROP and interval drilling using drilling parameter and bottomhole assembly (BHA) optimization. One fast run with an average of 45% better ROP was achieved on following runs. This saved seven drilling days and 2.5 runs; an average savings of 180,000USD per well.

This paper describes the collaborative solution and detailed technical optimization of hybrid bit performance in Gaoshiti-Moxi Block. Based on the drilling data, economic analysis of this project is also presented. With this cross-functional team’s effort, how this success model may apply on other drilling projects will be also included.

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