Study of Removing Formation Damage by Solidified Polymer in Extremely Hot Wells

Z. Krilov,* M. Tomic, B. Loncaric* and M. Cikes* The paper is describing the problem of identification of an inconvenient type of formation damage due to polymer solidification downhole. Laboratory tests showed the presence of this problem if particular temperature has been exceeded. Based on lab test results the method of chemical treatment was developed in order to remove this kind of damage. The comparison of laboratory investigation data and field application of method is expressed. The severe damage of production zones were occurred after using a gelled brine system for temporary viscous plugs set in some deep hot gas condensate wells in Southern Pannonian basin (BHT>195 C, TWD >4000m). Laboratory tests showed solidification of the same calcium bromide-calcium carbonate high activity synthetic polymer (polyacrilate) Water base system at temperature above 180 C. So formed viscoelastic material (solidified polymer) has plugged perforation tunnels and near wellbore porous medium, causing drastic reduction in well productivity. The laboratory tests and attempted well stimulation jobs showed that this type of residuum is practically undissolved in any well known solvent or acid. Due to further lab investigations the way of chemical treatment, using sequential injection of base (KOH) or oxidant (NaOCl + NaOH), following by inhibited organic acid (CH3COOH) was developed and successfully used in field practice to remove formation damage downhole. The described method of treatment, accompained with laboratory analytical procedure for damage identification, can be applied in designing the well stimulation jobs. P. 743