Development and Application of a Plugging-Type Solid-Free Drilling Fluid System

Area of Science:

• Geology and Petroleum Engineering
• Materials Science
• Fluid Mechanics

Background:

• Zhina coalfield has significant coalbed methane (CBM) resources with complex coal-body characteristics.
• Drilling in upper coal-bearing formations faces wellbore instability issues like spalling and collapse.
• Reservoir damage mechanisms in CBM drilling require effective mitigation strategies.

Purpose of the Study:

• To investigate reservoir damage mechanisms in CBM drilling.
• To develop a plugging-type solid-free drilling fluid system for enhanced wellbore stability.
• To optimize fluid loss reduction and sealing capabilities in CBM formations.

Main Methods:

• Core analysis using X-ray diffraction (XRD) and scanning electron microscopy (SEM).
• Hydration stability and mechanical property tests on coal and adjacent strata cores.
• Development and characterization of a novel fluid loss reducer and viscosifier (AMSN).
• Sand bed plugging tests and rheological property evaluation of the drilling fluid system.

Main Results:

• AMSN, a high molecular weight polymer, forms a stable 3D network, enhancing viscosity and thermal resistance.
• The developed drilling fluid system demonstrated excellent plugging capability (0 mL filtration volume) and lubricity.
• Field applications confirmed reduced wellbore enlargement and improved cementing quality in collapse-prone coal seams.

Conclusions:

• The developed plugging-type solid-free drilling fluid system effectively enhances wellbore stability in CBM wells.
• AMSN significantly improves fluid loss control, sealing, and thermal resistance, crucial for CBM drilling.
• The optimized system mitigates coal seam damage and improves overall drilling efficiency and well integrity.