Activator Development for Controlling Degradation Rates of Polymeric Diverting Agents

Abstract

Summary Hydrolytically degradable polymers (generally aliphatic polyesters) have been used in a variety of applications in the oil field, such as fluid diversion, fluid-loss control, and filter-cake-removal applications. In general, diverting agents and fluid-loss-control materials are only necessary to perform the intended function for a finite amount of time. Once the well is completed or placed on production, it is desirable that the degradable materials be removed so that they no longer have any influence on subsequent fluid flow. With time and temperature, the degradable polymers will break down by forming water-soluble byproducts, leaving behind limited, if any, residual formation damage. The effective formation sealing by these materials while in place, and eventual cleanup, has made them sought after materials for a growing number of applications. However, for cooler temperatures and applications for which the well must be placed on production rather quickly, there have not been many options to controllably increase the rates of polymer degradation. Strong acids and bases are known to accelerate the degradation of polyesters. Use of these materials can present several disadvantages, such as corrosion and/or undesirable reactions with the formation. This paper discusses amine- and aminoalcohol-based compounds as potential degradation accelerators (DAs) of polymers containing ester-functional groups in the polymer backbone. Oligomeric polyamines, such as ethylenediamine (EDA) and its homologues, and aminoalcohols, such as ethanolamine (EA), were tested as accelerators for polymer breakdown. Commercial polyesters tested in this study had variable crystalline and amorphous content. With one exception, polyglycolic acid (PGA), all polyesters contained polylactic acid (PLA)/polylactide either exclusively or as one of the components. The tests were performed under static conditions by aging known quantities of particulate polymers with identical particle-size distributions in excess aqueous fluids, and loss in recovered dried mass was measured periodically at test temperature. The results indicated that oligomeric polyamines accelerated polymer degradation significantly compared with water. The degradation rates were the highest for totally amorphous polymer and decreased with the increase in crystallinity. Some semicrystalline polymers appeared to increase in weight initially before manifesting weight loss because of degradation, especially in the presence of a polymeric amine, and to a lesser extent in the presence of water. Among aminoalcohols, EA containing a primary amine group was significantly more effective than that containing a tertiary amine in degrading semicrystalline polymers. Trialkanolamines appeared to cause swelling of the particulate semicrystalline polymers before significant weight loss from degradation manifested. Mechanistic implications of the results relating the degrading chemicals and the polymer properties and compositions are proposed.