Formation damage assessment in carbonate reservoirs after removing hematite-water-based filter cake using HCl

Area of Science:

• Petroleum Engineering
• Reservoir Engineering
• Materials Science

Background:

• Effective filter cake removal is critical for restoring formation permeability and productivity in open-hole completions.
• Hydrochloric acid (HCl) is commonly used for filter cake dissolution but can cause secondary formation damage via iron precipitation and pore plugging.
• Primary damage occurs during drilling from mud filtrate invasion and filter cake deposition.

Purpose of the Study:

• To investigate the relative contributions of primary and secondary damage mechanisms during hematite-water-based filter cake removal in carbonate reservoirs.
• To evaluate the impact of two operational strategies, squeeze and flowback, using 10 wt% HCl.
• To differentiate and quantify the effects of primary versus secondary damage on formation properties.

Main Methods:

• Core flooding experiments were conducted on Indiana limestone samples under representative downhole conditions.
• Formation damage was assessed using permeability, resistivity, CT imaging, and mechanical property measurements.
• Two operational strategies, squeeze and flowback, were directly compared for filter cake removal efficiency and damage mitigation.

Main Results:

• Primary damage alone reduced permeability by up to 75%.
• Secondary damage, particularly iron precipitation, was more severe in the squeeze treatment, impacting far-zone permeability and stiffness.
• The flowback strategy improved near-wellbore permeability and minimized secondary damage in deeper zones, preserving petrophysical and mechanical integrity.

Conclusions:

• Operational strategy significantly influences the dominant damage mechanism during filter cake removal.
• The flowback strategy is superior to the squeeze strategy for mitigating secondary formation damage in hematite-weighted filter cakes.
• Integrating mechanical property analysis with petrophysical evaluation provides a comprehensive understanding of reservoir damage and mitigation.