While originally developed for fracturing, manmade ceramic proppants are sometimes used for gravel packing wells. This is primarily due to their improved performance. However, the high solubility of ceramic proppants present in cleanup acids is a cause for concern when these proppants are used in gravelpacking. This paper presents the results of a study investigating the effect of cleanup acids on the solubility and compressive strength of commercial graveland ceramic proppants used in gravel packing.
A laboratory setup was designed to simulate material in a perforation tunnel. It included a Hassler core holder and lead sleeve mounts. Pre-flush, acid stages, and post-flush were pumped through the confined gravel and exposure time simulated field pumping times. Following acid exposure, thesamples were checked for weight loss, submitted for SEM analysis, and tested for crush resistance. Fines and oversize particle generation were compared to untreated samples using standards set forth in API-RP 58.
It is possible that a perforation will plug during the acid stage. Since a plugged perforation would prevent a sweep by the postflush, gravel in the perforation would be exposed to live acid indefinitely. To gain insight into the effect of prolonged acid exposure, a sample of ceramic proppant and 12:3mud acid + corrosion inhibitor was placed into a mud aging cell and heated for five days. Afterwards, the sample was checked for weight loss, submitted for SEM analysis, and tested for crush resistance.
Results of this study found that the effect of weight loss does not impact crush resistance when tested in accordance with the API-RP 58 gravel packing quality control procedure.
Selecting a gravel/proppant for sand control involves balancing several factors including performance and cost. Synthetic ceramic proppants are prized for their superior flow capacity (believed to arise from the individual grains'increased roundness and sphericity). However, laboratory studies indicate that ceramic proppants possess high acid solubilities. Also, unfavorable field experiences involving acid and ceramic proppants have been documented.