The Use of Biodegradable Particulate Diverting Agents in Hydraulic Fracturing and Refracturing: An Experimental Study

Abstract

A significant factor affecting the success of stimulation treatments is maximizing the stimulated reservoir volume. There is a tendency for stimulation fluids to follow the path of least resistance. This includes zones with high permeability and low stress as well as perforation clusters that have already been treated. As a result, stimulation fluids can bypass regions that could benefit the most from treatment. It may be possible to solve this problem by using particulate diverting agents which help create complex fracturing systems and increase the stimulated reservoir volume. The use of biodegradable particulate diverters in hydraulic fracturing and refracturing operations has shown promising results in numerous published lab and field studies. It was revealed that the use of these particulates could increase production, lower costs, and improve the overall well economics. However, some still question their effectiveness for many reasons including inconsistent downhole placement of particulates, especially in horizontal wells. Another issue associated with these diverters is the slow degradation rates seen in the field that cause delays in flowback from the plugged zones. In this research, biodegradable particulate diverters made from polylactide (PLA) were tested using an automated permeability plugging apparatus (APPA) under different conditions. A total of 56 APPA tests were conducted to determine the variables that influence the plugging performance of these particulates. The tested variables include diverters’ physical characteristics, diverter mass, temperature, differential pressure, and heating and pressurization duration. According to the results of this study, temperature significantly impacts the plugging performance of biodegradable particulate diverters. The ability of these diverters to deform above their glass transition temperature (Tg) results in enhanced plugging performance, while utilizing significantly lower amounts of particulates with a one-size distribution. The surface of PLA particulates softens above Tg and becomes flexible and rubbery. This deformation, in turn, can cause the particulates to fuse together and form a plug capable of sealing perforations and large fractures. Upon cooling down to room temperature, the particulates solidify again and remain fused, demonstrating their ability to remain intact during the cooler portions of hydraulic fracturing treatments. Additionally, different shapes and sizes of biodegradable particulates behave differently above Tg. Contrary to conventional diverters, the lower permeability of the diverter pack does not result in enhanced diversion efficiency for these biodegradable diverters above Tg. This difference in behavior at different temperatures helps explain the inconsistent results observed by many operators when used in hydraulic fracturing and refracturing operations where downhole temperatures vary considerably. In the field, these differences in behavior at various temperatures can cause unfavorable consequences if unaccounted for. Guidelines for using biodegradable particulate diverters are proposed, and recommendations are made regarding their use above Tg to ensure effective plugging and successful diversion. It is anticipated that these guidelines will help resolve many issues experienced in the field, such as inconsistent placement, slow degradation rates, and long flowback times.