i-DRILL study

A comprehensive i-DRILL modeling project was planned to determine contact forces on the BHA. These included an examination of rock strength analysis, fundamental PDC shearing action, and the effects of variation in drilling parameters. The goal would be to maximize ROP and mitigate drillstring vibration through several efforts: select the best PDC bit and directional steering tool, and determine the best combination of drilling parameters. Each component would be evaluated on four criteria:

• lateral, axial and torsional vibration
• surface and downhole torque
• instantaneous ROP
• directional prediction (buildup rate and walk rate).

Before running the dynamic simulations, it was essential to calibrate the model with offset data to ensure accuracy of the optimization process. A virtual representation of the application was produced to quantitatively investigate iterative changes to BHA components and bit design. In this case, ROP was the reference point for adjusting the model, but the process enables other variables to be used such as vibration and torque. To gain inferences about the target formations, DBOS drillbit optimization system was used to analyze rock strength based on offset data. To simulate these characteristics, several rock files were tested in the IDEAS platform and analysis laboratory to find a sample that would best reflect the physical properties of the formation.

Selecting proper PDC bits

The next step was to select the appropriate PDC bit candidates for the i-DRILL investigation. Based on previous experience, engineers selected three 8 1/2-in IDEAS platform–certified PDC designs: A MDi613, MDi616, and a MDSi813 were chosen for the simulation. Personnel from Schlumberger recommended a fixed BHA with a PowerDrive Xceed point the bit RSS and nine combinations of operating parameters: 10K-, 15K-, 20K-lbf WOB and 120-, 130-, and 140-rpm surface rotary speed. The finite elements analysis (FEA) -based modeling system was then used to run dynamic simulations with various combinations of bits and parameters. The virtual analysis revealed all three PDCs met surface torque requirements, but the MDi613 was eliminated because did not present the best dynamic response for this particular application. Additional testing showed the MDi616 displayed better directional response compared to the MDSi813 design. After reviewing all simulation results, engineers determined that an 8 1/2-in MDi616LEB run with 10,000-lbf WOB and 140-rpm rotary speed would drill the lateral hole section with minimum vibration and at a maximum ROP. OGX and Schlumberger personnel agreed with the analysis and supported the recommendations.

Performance results

After drilling to the kickoff point at 3,746 m, the MDi616 was run on a PowerDrive Xceed RSS and drilled a 1,000-m, 8 1/2-in lateral borehole into the carbonate pay zone with minimal vibration and no directional issues. The bit delivered all trajectory requirements, doubled ROP compared to the correlation offset, and was pulled in excellent dull condition (0-0). The driller closely adhered to the optimal parameter combination (WOB and rpm) produced by the i-DRILL drilling system analysis. As a result, the operator saved 2.6 days of rig time, for an approximate savings of USD 1,300,000, as compared to the AFE plan.