The impact of the fracturing additives on the near fracture face matrix permeability for shale and low permeability sand formations

In the present study, the effect of the fracturing additives on the near fracture face matrix permeability of shale and low permeability sand formations is investigated for different scenarios of the fracturing treatment design. The first scenario evaluates the impact of the pad fracturing fluid on the near fracture face matrix permeability. The considered pad fluids are friction reducer, friction reducer with a nonionic surfactant, and 3 wt% HCl. The second and third scenarios investigate the effect of injecting slugs of a nonionic surfactant and 3 wt% HCl during the main fracturing treatment on the near fracture face matrix permeability. The HCl acid treatment was considered only for the outcrop shale core samples that are representative to the Carbonate-rich Upper Eagle Ford formation and Carbonate-rich Marcellus lower member. Constant rate liquid flooding apparatus was used to measure the core samples brine (3 wt% KCl) permeability at atmospheric temperature and to flood the samples with friction reducer fluid or friction reducer with a nonionic surfactant fluid at 200^oF. A pressure vessel was also used for shale samples aging in 3 wt% HCl under high pressure and temperature to investigate the proper shale-acid contact time and to prepare the acid treated samples for the permeability measurements. The results of the first scenario showed that the polymer adsorption from the friction reducer fluid significantly reduces the brine permeability of low permeability sand samples and for shale samples, though to a lesser degree. On the other hand, the nonionic surfactant and the 3 wt% HCl increased the brine permeability of all samples. Therefore, the friction reducer fluid reduces both of the fluid flowback and fluid loss into the formation and the reverse is true for the friction reducer with a nonionic surfactant fluid and 3 wt% HCl. Moreover, the HCl acid increases the porosity and the fluid loading near the fracture face, thereby increasing the fluid loss. The second scenario showed that the polymer adsorption during the pad stage and the shale heterogeneity affect the impact of the nonionic surfactant used in the main fracturing treatment to enhance near fracture face matrix permeability. Moreover, the second and third scenarios showed that the shale samples carbonate content, heterogeneity, Nano permeability, polymer adsorption, and iron precipitates control the success of using dilute HCl acid on enhancing near fracture face matrix permeability.