Design and development of CaCO₃nanoparticles enhanced fracturing fluids for effective control of leak-off during hydraulic fracturing of shale reservoirs

This research presents new information about the nanoparticles (NPs) use as a filtrate reducer in the hydraulic fracturing of shale reservoirs. An experimental study was conducted to determine the filtration loss control effectiveness (FLCE) of CaCO₃NPs as an additive in fluids used for hydraulic fracturing of the shale reservoirs. The main objectives were (i-) to determine the mechanisms controlling the NPs enhanced fracturing fluid leak-off rate; (ii-) to determine the optimum NPs concentration, which yields the best FLCE. Spontaneous and forced imbibition experiments (to determine imbibition index) as well as the pressure transmission tests (to determine liquid permeability) were conducted using water based fracturing fluids enhanced by CaCO₃NPs. The imbibition index and the apparent liquid permeability measurements were then used to determine the impact of the NPs concentration (i.e. 0.0, 0.5, 1.0, 2.0 wt%) on the FLCE. In order to understand the filtration control mechanisms of the NPs enhanced fracturing fluids, we have analyzed the field emission scanning electron microscope (FESEM) images of the shale samples, which provided detailed description of how NPs are attached to the shale surface. The experimental results indicated that the CaCO₃NPs have excellent FLCE. The imbibition index and the apparent liquid permeability decreased significantly along with the increasing NPs concentration. The optimum NPs concentration was found to be 1.0 wt%. Analyses of the FESEM images demonstrated that the distribution of the NPs on shale surface is selective. The NPs mainly attached on the rough areas of the shale surface. The process of the NPs adsorption-sealing leads to the reduction of the path of the fluid flow into the shale matrix, and in turn, controls the fracturing fluid filtration. Ultimately, four kinds of sealing patterns were observed including (i-) plugging, (ii-) bridging, (iii-) plugging and accumulation, (iv-) bridging and accumulation.