Construction and phase transition characteristics of nano-graphite-induced rapid growth self-generated proppants

To solve the problem that the self-generated proppant in fractures grows slowly and cannot support the fractures in time, nano-graphite (NG) was introduced into a phase change liquid (PCL) composed of “styrene-divinylbenzene (SDB)” and the resulting self-generated proppants were constructed with a high growth speed. The NG/PCL started the phase transition from liquid to solid after 8 min at about 55°C in the wellbore section, and the phase transition was completed for only 2.5 min at a constant temperature of 65°C in fracture. Moreover, due to the high thermal conductivity and heterogeneous nucleation of the NG powder, the maximum strength of self-generated proppant in the NG-containing system can reach about 56.2 N during its growth process, which is 34.4% higher than that of pure SDB. The yield of the well-dispersed spherical self-generated proppants NG/SDB under the completely static condition can reach about 80%, of which the proppants with a particle size of 0.4 ~ 0.7 mm account for about 80%. NG/SDB exhibited an ultra-low apparent density of approximately 1.004 g/cm 3 , high compressive strength, and a crushing ratio of less than 1% at a closure pressure of 52 MPa, which is lower than that of commercial quartz sand and ceramsite proppants. Highlights Self-generated proppants with rapid growth were developed by the introduction of NG. Positive effects of NG in PCL system are obvious on phase transition and growth. NG/SDB is qualified in phase transition timing and compressive strength. The single-microsphere yield of NG/SDB is about 80%. The crushing ratio of NG/SDB as low as 3.92% at a closure pressure of 69 MPa.