Coring 101: Episode 1 - What is Coring?

Introduction

• Speaker: Tim Clark, Founder of Corizon Wellfield Services
• Topic: Overview of coring in reservoir rock sampling.

Definition of Coring

• Coring is the acquisition of intact samples of reservoir rock.
• Provides more representative samples of the downhole environment compared to cuttings.

Methods of Coring

1. Conventional Rotary Coring

• Involves running a specialized drilling assembly to cut a column of reservoir rock.
• Core head is a special drill bit without a center.
• Modern coring uses:
  • PDCs (Polycrystalline Diamond Compact) bits
  • Diamond and impreg bits.
• Components of the core system:
  • Outer Core Barrel:
    • Made of large diameter steel drill pipe.
    • Typically under gauge (e.g., 3/8 inch).
    • Stabilized regularly (typically every 30 ft).
  • Inner Core Barrel:
    • Made of aluminum to minimize friction.
    • Suspended from the inner head bearing assembly.
• Process:
  • Core head cuts the formation, leaving a cylinder of reservoir rock.
  • Inner core barrel moves over the core to protect it.
  • Upon completion, the core barrel is recovered to the surface.
• Core size:
  • Diameter ranges from 1 3/4 in to 5 1/4 in.
  • Typically cut in 30 ft increments; can exceed 600 ft but 90 to 180 ft is common.

2. Side Wall Coring

• Acquires plug samples from the wall of the borehole.
• Taken as part of the open-hole wireline logging program.
• Typically measures:
  • Length: 1 1/8 in to 1 3/4 in.
  • Diameter: 11/16 in to 1 in.
• Conducted after logs are run, usually near the end of wireline logging.
• Enables geologists to select zones of interest based on log consultation.

Conclusion

• Importance of coring:
  • It's the only opportunity to physically touch and evaluate the reservoir.
• Next episode will discuss why coring is performed.