Laboratory evaluation of micro-proppants on enhancement of microfracture conductivity in unconventional reservoirs

The complex fracture network generated from hydraulic fracturing is of great importance for well productivity in unconventional reservoirs. However, numerous natural or induced microfractures are closed without proppant placement after hydraulic fracturing is completed. Micro-proppants have small enough particle sizes and longer transport distances, which can access microfractures and keep them open. The objective of this work is to investigate the particle size distribution, crushing rate as well as microfracture conductivity by micro-proppants from fly ash. Microproppants have a large range of particle size from 1 μm to 300 μm, and the average particle diameters are 22.84 μm and 51.13 μm. The crushing rates of micro-proppants are related to the particle size distributions and mineral contents. More concentrated distribution of particle sizes and higher contents of high-hardness minerals lead to a lower crushing rate of micro-proppants. The fracture conductivity is exponentially decreased with closure stress, and it is controlled by average particle sizes and crushing rates of micro-proppants. The results demonstrate micro-proppants from fly ash are sufficient to the requirements of hydraulic fracturing and improve hydrocarbon production of unconventional reservoirs.