Schlumberger

Case Study: SHARC PDC Bit and PowerDrive Archer RSS Save Operator USD 9.8 Million Offshore Australia

Precise directional control reduces sidetracking, improves borehole quality

Challenge: Drill high dogleg borehole with PDC and RSS drilling system, reduce the BHA’s tendency to drop inclination through the unconsolidated reservoir sand offshore Australia.

Solution: Use IDEAS drillbit design to modify a standard SHARC PDC bit by optimizing the drillbit blade count, cutting structure exposure, and nozzle configuration, and pair it with a PowerDrive Archer RSS to accomplish the operator’s objectives.

Result: The SHARC bit and PowerDrive Archer RSS to consistently held inclination through the drop zone and drilled horizontally in a high ROP environment. It marked the first time a PDC and RSS were combined with this result. Increased directional control reduced sidetracking and improved wellbore quality. This enabled a quick screen deployment saving the operator USD 9.8 million.

High-build rate RSS with system matched PDC bit required

The operator is using extended reach horizontal drilling techniques to develop lower Cretaceous oil reserves offshore Australia. During the initial phases of the drilling campaign, the operator was forced to construct a 9 1/2-in section with a bent angle positive displacement motor (PDM) drive system to deliver the dogleg requirements and effectively geosteer in the reservoir. PDM drilling proved costly and time consuming, resulting in poor and tortuous borehole, which limited horizontal reach. The operator experimented with two different rotary steerable systems with limited success. The major issue was the inability of a standard dogleg RSS to maintain wellbore trajectory drilling through a drop zone composed of unconsolidated reservoir sand. This required expensive sidetracking to correct wellbore trajectory, a conventional PDM BHA or both to reach TD. In some cases, another trip was needed to continue drilling with a RSS. Rollercone tungsten carbide insert (TCI) drill bits were used because of rig torque delivery limitations, but a three year design initiative resulted in several new TCI footage and ROP records.

Drilling strategy: Phase III

Before launching Phase III development, a team of well construction professionals brainstormed specific drilling operations to determine areas for potential improvement. The plan was to design a drilling system that would provide precise trajectory control and the capability to drill the drop zone without sidetracking or tripping for a BHA change out. The team concluded that the PowerDrive Archer’s RSS high build-rate capability could solve a multitude of application issues associated with PDM drilling systems. The PowerDrive Archer dogleg capability would enable it to cross dropzones and steer through obstacles that proved difficult for standard RSS.

The solution would provide all the traditional advantages of using RSS, including enhanced wellbore quality, better hole cleaning and more effective geosteering in the reservoir. However, the new BHA would require a system matched PDC bit with proper blade count and cutter configuration to ensure optimal directional response and drillstring stability. Other changes included a switch to water based mud, a reduction in hole size to 8 1/2-in and rig modifications to provide the required torque to efficiently drive the SHARC high-abrasion-resistance PDC drillbit and bottom hole assembly.

Engineering assessment

Since most of the offsets were drilled with a rollercone and PDM assembly, only six applicable PDC/RSS runs were available for analysis. A dull grading exercise revealed bit body erosion caused by cuttings recirculation and vibration induced cutter chipping. Any new PDC design would need to address these issues. Relying on limited data could prove problematic and force the operator into a trial and error approach to develop a matched PDC bit. To avoid field trials, designers used IDEAS drillbit design platform to evaluate several different PDC cutting structures in a virtual environment that matched the operator’s application to determine which base design offered the best combination of directional responsiveness, high ROP potential, and stability for the directional profile and formations to be drilled.

Over 200 simulations were run, after which iterative changes were made to the bit, resulting in the final 8 1/2-in SHARC MDSi716LKUBPXX design. Specific modifications include:

  • diamond-impregnated depth-of-cut control feature to reduce torsional vibration/ensure blade top durability
  • CFD modified hydraulic layout to mitigate cuttings recirculation
  • high-erosion resistant matrix bit body
  • modified gauge pad length with diamond protection

Integrated tool solution produces win-win scenario

The application of the IDEAS designed SHARC bit on a PowerDrive Archer RSS successfully delivered the required directional work on the two wells/five laterals and consistently corrected inclination even while drilling the extreme drop zones where ROP reached 300 m/h. This was also the first time the PowerDrive Archer RSS was used in deepwater to geosteer horizontally in a high-ROP application rather than just for its ability to drill short radius borehole. The improved directional control and well placement capabilities eliminated the need for drop zone correction sidetracking. The BHA delivered a smooth high-quality wellbore, significantly reducing the time required to run openhole sand screens. This increased operational efficiency saved the operator USD 9.8 million.


Download: SHARC PDC Bit and PowerDrive Archer RSS Save Operator USD 9.8 Million Offshore Australia (0.68 MB PDF)

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