Cleanup of Wall-Building Filter Cakes

by
Zulkeffeli Mohd Zain, MSE

University of Texas at Austin, 1999
Supervisor: Mukul M. Sharma

This thesis presents the experimental results of mud cake lift-off tests. The aim of the study is to define the factors that affected the removal of filter cake through fluid flow after it is formed on a rock surface. Improved fluid designs are important to address the use of drilling and completion fluids with effective cleanup ability.

The experiments were performed using a HPHT filter cell. Core samples with permeability range of 3 to 2000 md were used. Most of the findings were made based on the cleanup of sized CaCO3 and sized salt drill-in fluids. Parameters such as mud type, rock permeability, filtration pressure, flow rate, pore throat diameter, and solid particle size were considered in this study.

The results show that sized CaCO3 fluids require lower flow initiation pressures and are less damaging than sized salt fluids. Low permeability rocks (smaller pore size) experience less internal formation damage and need relatively high flow initiation pressures compared to high permeability samples. Total mud cake removal is observed for experiments with limestone cores while only cracks and small holes were seen for experiments with sandstones. A filter cake of small particle fluid system is also easily removed. High overbalance pressures were also found to increase the magnitude of the flow initiation pressure.

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