Zero Flowback Rate of Hydraulic Fracturing Fluid in Shale Gas Reservoirs: Concept, Feasibility, and Significance

Abstract

A high flowback rate of hydraulic fracturing fluid (HFF) yields a high gas production rate in a tight sand gas reservoir. This idea is well followed when it comes to the hydraulic fracturing of a shale gas well. Therefore, numerous studies have focused on increasing the flowback rate of HFF in shale gas reservoirs to mitigate the water blocking damage. Yet, only a small portion of the injected fluid (less than 20%) could be recovered during flowback operation. Moreover, there is no good correlation between the gas production rate and flowback rate for shale gas wells. Surprisingly, a phenomenon that a low flowback rate of HFF usually yields a high gas production rate is found recently by field data studies. In this case, the authors investigated the reasons for this abnormal phenomenon and believed that reducing the flowback rate of HFF in a shale gas reservoir could be a new strategy for dealing with the injected HFF. Therefore, a new concept called zero flowback rate (ZFR) of HFF is put forward to serve as an unconventional way to manage the high volume of HFF. ZFR of HFF is a concept compared with the flowback rate of the fracturing fluid for a conventional reservoir. It is worth noting that zero in the ZFR concept does not stand for the absolute number 0. It means that reducing the flowback rate of HFF is the goal of the ZFR strategy. To analyze the feasibility of realizing ZFR, the geological conditions of gas shale and engineering conditions of hydraulic fracturing were evaluated by comparing the relative studies. It showed that gas shale has the potential to imbibe most of the HFF and retain the imbibed fluid without contaminating the groundwater. ZFR can be realized by extending the shut-in time or adjusting the properties of HFF. Compared with the conventional idea of increasing the flowback rate of HFF, ZFR is of great significance. It does not only recover the relative gas permeability of the shale reservoir by redistributing the liquid phase from the fractures into the shale matrix but also enhances it by creating new microfractures. ZFR is cost-saving and environmentally friendly by dealing with a reduced volume of flowback HFF. ZFR has a high potential of becoming a viable strategy for the development of shale gas reservoirs.

Study on Formation Damage of Fracturing and Its Prevention through an Environmentally Friendly Method of Oxidative Stimulation in Shale Gas Reservoirs

“…A large number of studies have also confirmed that residual fracturing fluid can promote fracture propagation through water–rock interaction during shut-in . Based on this, researchers demonstrated the feasibility of utilizing the positive effect of residual fracturing fluid to create fractures by reducing the amount of flowback fluid and believed that this was a feasible strategy for the efficient development of shale gas reservoirs . In this paper, the oxidative stimulation method is proposed.…”

Progress and Prospects of Supercritical CO2 Application in the Exploitation of Shale Gas Reservoirs

“…On the one hand, some scholars stated that low viscosity represents weak proppant carrying capacity, small induced fracture width, low flowback rate, and large reservoir damage, which is not conducive to gas production, ,, whereas some scholars also suggested that the pore pressure field and thermal stress caused by low viscosity and high diffusion coefficient of SCCO 2 jointly reduce the effective stress and induce the shear failure of natural fractures so that it is easier to enter the primary fractures of the reservoir by pressure infiltration and promote the formation of the fracture network. ,, Furthermore, today’s shale reservoir flowback rates are all low (<20%) of injecting fluids, and the low flowback corresponds to higher gas production by observation in the production process of several shale gas reservoirs. Thus, the industry is also trying to increase the “soaking time” or zero flowback rates for better production. − …”

Molecular Origin of Wetting Characteristics on Mineral Surfaces

“…The molecular-level structures and chemistries of mineral surfaces are also expected to influence the wetting characteristics and thus make the problem more complex. Furthermore, these wetting characteristics not only play a crucial role in the wetting process but also profoundly influence the processes of flow, displacement, and imbibition in porous media. ,− A typical example is the spontaneous imbibition process of hydraulic fracturing fluid into shale reservoirs, where the amount of water lost can be severely overestimated if the influences of precursor films and dynamic contact angle are not considered. , …”