As we all know, the proppant sizes are generally between 8 and 140 mesh (105 μm-2.38 mm). The mesh size is the number of openings across one linear inch of screen. When describing the size of the proppant, the proppant is often referred to as simply the sieve cut. For example, 16/30 mesh is 595 μm-1190 μm; 20/ 40 mesh is 420 μm-841 μm; 30/50 mesh is 297 μm-595 μm; 40/ 70 mesh is 210 μmm-420 μm; 70/140 mesh is 105 μm-210 μm. Typically, larger particle sizes provide higher fracture conductivity. In order to gain more heat from EGS in the long-run, hence the fracture conductivity is less important than fracture complex, so my question is what's the usual size of proppant in EGS, the larger one or smaller one?
FYI:
https://repositories.lib.utexas.edu/handle/2152/34589
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EGS projects have not used multiple stages, proppant, and horizontal (or deviated) wells either (1) because it was believed that they would not be effective or (2) because of the technological challenges of operating at high temperature in hard rock. There appears to be skepticism in the EGS community about using proppants. One argument is that proppants will chemically degrade in the highly reactive environment of an EGS reservoir. Another argument is that proppants are unnecessary because fractures in granite are "self-propping" and have high transmissivity even when not propped. A third potential concern about proppant is that it may lead to the formation of thermal short-circuit pathways. Proponents have touted an "advantage" of shear stimulation (induced slip on pre-existing fractures, relying on the transmissivity of unpropped fractures to create stimulation) is that it generates distributed fracture networks, which should reduce short-circuiting by distributing flow into a more volumetric fracture network. But these pathways have generally been shown to have poor, unpredictable connectivity and inadequate overall permeability. Furthermore, it seems counterintuitive that we should avoid using proppants because they could create short-circuit pathways. Short-circuit pathways are high transmissivity pathways for flow, and inadequate flow rate is the principal obstacle preventing widespread adoption of EGS. To combat short circuiting, multiple stages could be used. Multiple stages would inhibit short circuiting because it would force fractures to form at each stage. Proppant has been used at a limited number of EGS projects in granite. In every case, proppant has been placed successfully and increased fracture transmissivity. The earliest experiment was a small test at the Fenton Hill project in 1974 involving injection into an openhole section isolated with packers. In the first test, injection was performed, and there was limited fluid recovery during subsequent flowback. Fluid was believed to be entering a natural fracture that was opening in response to injection. Injection was repeated with proppant, and almost full recovery was achieved. The implication is that without proppant, the natural fracture at the wellbore closed during flowback and hydraulically isolated the remaining injection fluid away from the wellbore. With proppant, the fracture retained transmissivity when it closed during flowback, enabling nearly full recovery. Evidently, the natural fracture had much greater transmissivity (post-closure) when filled with proppant. The first large experiment with proppant at an EGS project was in the well RH15 at Rosemanowes (Bennertt & Barker 1989). Proppant was injected with viscous gel at high rate into an openhole section roughly 150 m long. Production logs showed that after stimulation, the main conduit for flow at the well was a single fracture, believed to be where the injected proppant had gone (Bennertt & Barker 1989). Parker (1999) reported that the proppant placement resulted in a significant lowering of system impedance and water loss during circulation. The proppant was so effective at improving connectivity that it was blamed for worsening a thermal short-circuit. "
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