Abstract
During hydraulic fracturing treatments, proppants often settle near-wellbore in low viscosity fracturing fluids (e.g., slick water) and leave a large fractured surface unpropped. Poor placement of proppant could lead to a loss of fracture conductivity and undermine the productivity of shale wells. In addition, lots of microfractures are too narrow to accommodate commercial proppants and would close during production. In this study, a hydro-thermal reaction is proposed to generate hydroxyapatite crystals on calcite-rich shale surface to act as in-situ proppants to improve fracture conductivity. First, batch experiments were conducted in both low salinity frac water and seawater brine. Crystals were generated in both low and high salinity (and hard) brines. The crystals grew to several hundred microns and tended to form along calcite-rich layers, according to SEM image analysis. The hardness data showed that properly designed formulations could avoid the shale softening effect. Second, reactive flow experiments were performed to evaluate fracture conductivity change after chemical treatment. A typical 3-10 times increase in post fracture conductivity was observed for both reservoir and outcrop shale samples.
