Case Study: ONYX II PDC Cutters Set New China ROP Benchmark, in Abrasive Triassic Sandstone

SHARC drill bit reduces average cost per meter by 57%

Challenge: Drill 800 m of abrasive Triassic sandstone at the highest possible ROP with fewest number of PDC bits.

Solution: Launch multi-pronged research initiative to develop and manufacture new abrasion resistant cutter technology. Apply DBOS rock strength analysis and IDEAS drillbit design platform to design a PDC bit body to fully exploit the ONYX II cutter’s ability to retain a sharp edge in demanding formations.

Result: Set new field benchmarks for fastest ROP and lowest cost/meter compared to six offsets drilled through the same section.

Stable PDC bit equipped with durable cutters required

The operator must penetrate approximately 800 m of highly abrasive quartzitic sand interbedded with hard siltstone stringers to access the reservoir in a south China gas producing region. The majority of the thick Triassic formation has unconfined compressive strength (UCS) that fluctuates between 15,000–21,000 psi with hard stringers reaching 30,000 psi. The difficult downhole environment has caused extreme PDC cutter wear in addition to impact induced breakage. The abrasive wear and bit damages lows ROP to a non-economical level forcing the operator to make 3–5 bit runs to complete the 12 1/4-in vertical hole section. The excessive NPT and bit spend is driving up field development costs and damaging project economics. The operator requires durable PDC cutter technology that can stay sharp to increase ROP and extend total footage capabilities.

ONYX II PDC cutter development

To develop a new cutter for the Chinese application, Smith Bits assembled a cross functional team including experts from R&D, engineering and manufacturing. The research initiative would concentrate on developing technologies to improve the cutter’s resistance to abrasive wear. The scientific investigation indicated that thermal fatigue is one of the main contributing factors leading to cutter failure and is restricting further advancement of PDC drilling in south China. To improve cutter performance the industry must:

  • manufacture a cutter to resist abrasive wear and retain a sharp edge for an extended amount of meterage
  • reduce and maintain temperature at the cutter edge to minimize thermal fatigue.

To accomplish the objectives, engineers refined and implemented several new processes to increase abrasion resistance and maintain temperature at the cutter tip including:

  • Increasing density/packing of diamond structure
  • Refining the post-pressing process to improve thermal stability
  • Synthesizing the diamond table under extreme HPHT conditions

The initiative led to knowledge gains in materials science and enhanced manufacturing processes that resulted in ONYX II PDC cutter technology. In laboratory wear index tests, thenew cutter has demonstrated a 15% improvement in resistance to abrasive wear compared toother premium shearing elements. In field tests, ONYX II has achieved an average ROP increaseof 15% while improving overall dull bit condition. The ability of the new cutter to retain a sharpedge has the potential to increase ROP and footage totals in the south China application.

IDEAS drillbit design system

To fully exploit the ONYX II cutter advantage requires a dynamically stable bit body with the proper blade count and optimized cutter configuration. To avoid the trial and error approach, engineers used the IDEAS platform rock sample laboratory and modeling system to create a real-world virtual environment to develop the PDC bit solution. Engineers selected four base designs for the modeling study. A DBOS rock strength analysis was run on a variety of abrasive sandstones to determine which lithology is most similar to the actual field formation. The investigation revealed that Colorado Tan sandstone, with a UCS of 20,000–30,000 psi, would be best suited for the simulation. A single-cutter scrape test was performed in the laboratory to replicate 6000 ft of straight hole drilling with 30,000 lbf WOB at 110 rpm surface rotary speed. The test results were then analyzed using IDEAS drillbit design platform and a wear-flat simulation was performed using seven- and eight-bladed designs to determine the degree and location of cutter attrition. The analysis determined a 12 1/4-in MDSi716 with 16 mm ONYX II PDC cutters would provide the best configuration to resist abrasive wear. Next, a stability simulation was run which generated a unique bottomhole signature that clearly demonstrated the MDSi716 is the most stable design for the application. The IDEAS drillbit design process delivered value by enabling designers to observe how the bit interacted with actual formation as an integral part of the total drilling system. This allowed them to analyze the results of iterative design changes that rapidly advanced the engineering concept to an application specific PDC bit design.

ONYX II sets new benchmarks

The IDEAS designed 12 1/4-in MDSi716, fitted with ONYX II cutter technology, was run and set new field records for highest ROP and lowest cost/meter. The new style PDC bit drilled 32% more meters than the next longest bit run and 99% more meterage compared to the six well offset average. A ROP comparison shows the bit drilled 518 m of section at 7.6 m/h, 31% faster than the best offset and 65% faster than the offset average of just 4.6 m/h. The performance improvement resulted in a 46% reduction in cost/m compared to the best offset and 57% less than the six well average.

Download: ONYX II PDC Cutters Set New China ROP Benchmark, in Abrasive Triassic Sandstone (0.73 MB PDF)

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