Coring is the process of extracting a cylindrical sample of rock (called a core) from a subsurface formation during drilling operations. This core provides direct, unaltered physical evidence of the formation and is used for detailed geological, petrophysical, and reservoir analysis.
Types of Coring:
- Conventional Coring:
-Uses a core barrel attached to the drill string.
-Retrieves a solid core sample (typically 3–4 inches in diameter, 30–60 feet long).
-Common in exploration wells. - Sidewall Coring:
-Uses wireline tools to cut or punch small core plugs from the wellbore wall.
-Can be percussion or rotary type.
-Used after drilling has reached total depth. - Pressurized Coring:
-Cores are retrieved in a sealed pressurized chamber to preserve formation fluids and pressure.
-Useful for gas-rich or unconsolidated formations.
Purpose of Coring:
-Analyze porosity, permeability, and fluid saturation.
-Identify lithology and rock texture.
-Determine reservoir quality.
-Study natural fractures and sedimentary structures.
-Calibrate well logs and improve reservoir models.
Challenges of Coring:
-Expensive and time-consuming.
-Risk of core loss or core damage.
-Requires careful handling and preservation.
-Sometimes not feasible in unstable formations.
When is Coring Used?
-In exploration and appraisal wells.
-In zones of interest for reservoir evaluation.
-Where high-resolution geological data is required.
-Often performed before completion or stimulation operations.