Paper presented at SPE Middle East Oil and Gas Show and Conference, Manama, Bahrain, March 2013.
Filter Cake Cleanup Using HCl/Glycolic Acid System
Cleanup of filter cake generated by high density drilling fluids (1.5 SG) that are based on manganese tetraoxide (Mn3O4) particles as a weigthing material was investigated using a mixture of HCl and glycolic acids. Manganese tetraoxide (Mn3O4) has a specific gravity of 4.8, which means that it can be used to drill deep wells. Because of the hetrogenouty of the filter cake, it was suggested in the literature to degrade the top layer of the filter using an enzyme and dissolve the remaining filter cake using organic acid. HCl at concentrations greater than 5 wt% HCl releases chlorine gas, a toxic and corrosive gas. A Breaker fluid was developed, which combined low and safe concentration of HCl and glycolic acid. Solubility tests conducted at 250°F indicated that glycolic acid alone did not dissolve the filter cake. However, a combination of 7 wt% glycolic acid and 1 wt% HCl dissolved 90% of the filter cake. The acid mixture was tested in a modified HPHT filter press. Indiana limestone and Berea sandstone cores were used at 250°F. The cleaning fluid was very effective in removing filter cake, removal efficiency was nearly 90% and the return permeability was 100%. The filtrate into limestone and Berea cores did not cause any damage.