Abstract
The horizontal well multistage hydraulic fracturing technology is the most effective way to exploit shale gas resources. Compared with conventional reservoir fracturing, the flowback rate of a fracturing fluid in a shale reservoir is extremely low, and a large amount of fracturing fluid remains in the formation. Therefore, the research on the mechanism of shale reservoir fracturing fluid flowback process will contribute to laying a theoretical foundation for improving the effect of the innovation for increasing output of shale gas wells. Based on the shale in the Sichuan Basin, this study first describes basic experiments on physical properties such as the porosity, permeability, mineral composition, wettability, and microstructure. The physical properties of shale reservoirs were also analyzed, which laid the foundation for subsequent modeling. Second, CMG software is used to establish a numerical model that fits the characteristics of the flowback process. The effect of reservoir properties, fracturing parameters, drainage–production system, chemical permeability on gas and water production in the flowback process and their mechanisms are also analyzed. According to most numerical simulation results, the lower cumulative gas production will be with the higher cumulative water production which means the higher flowback rate. The pursuit of only a high flowback rate is not advisable, and the development of the drainage–production system requires reasonable control of the fracturing fluid flowback rate. This study provides a theoretical basis for the optimization of shale gas drainage–production system after hydraulic fracturing.
Highlights
As a clean, efficient, and unconventional resource with great potential, shale gas has been commercially developed in many countries around the world
The fracturing fluid that enters the reservoir through filtration will change the pore structure of the shale through spontaneous imbibition and hydration or osmosis, which can provide more gas flow channels to displace more gas and increase the cumulative gas production
The influence of most influencing factors on gas and water production shows that the higher the cumulative water production of shale gas well is, the lower the corresponding cumulative gas production will be
Summary
Efficient, and unconventional resource with great potential, shale gas has been commercially developed in many countries around the world. In order to study the influence of wettability, Fakcharonphol (Wang et al, 2016) constructed the relative permeability curves and capillary pressure curves of the reservoirs with high wettability, medium wettability, and low wettability (Figure 8 and Figure 9) It can be seen from the simulation results that as the degree of wettability decreases, the cumulative gas production decreases, and the cumulative water production gradually increases. Since the fracturing fluid entering deep into the reservoir causes water blocking, the influence of the fracture conductivity on the change of gas production will be small It can be seen from the simulation results about the effect of the number of fracture clusters on the production that the larger the number of fracture clusters is, the higher the initial gas production and cumulative gas production will be and the lower the flowback rate will be. The fracturing fluid will induce the formation of more microfractures under the effect of spontaneous imbibition and hydration, or make the originally closed natural fractures reopen, so as to displace more gas and improve production
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