Abstract
The chemical and physical capabilities of shale can be altered by the interactions between fracturing fluid and shale formation, affecting the long-term reservoir productivity. To obtain information regarding how fracturing fluids with different components impact the pore structure, porosity and mineral compositions of shale reservoir rocks over time, two different types of commercial fracturing fluids (slick water and crosslinked gel) were used to react with the shales from Longmaxi Formation of Lower Silurian in the Sichuan Basin of South China. Experiments were conducted with various time intervals (1, 4 and 10 days) in a reactor at 50 MPa and 100°C, and then analytical methods including X-ray diffraction, low pressure nitrogen adsorption, field emission scanning electron microscopy and porosity measurement were used to examine the changes of mineralogical compositions, pore structure and porosity. The results demonstrated that the mineral compositions of shale samples were significantly changed after treatment with two different fracturing fluids for 4 days. The analysis of field emission scanning electron microscopy revealed that the carbonate minerals were dissolved and developed many dissolution pores after slick water treatment, while the crosslinked gel mainly caused the precipitation of carbonate minerals. After exposure to different fracturing fluids, the total pore volume and specific surface area decreased over time. Moreover, the fractal dimensions (D1 and D2) of shale showed an apparent decrease trend after treatment with two different fracturing fluids, indicating that the pore surface and structure become smooth and regular. The porosity of shale significantly decreased by 15.9% and 17.8%, respectively, after 10 days of slick water and crosslinked gel treatment. These results indicated that the injection of the two different types of fracturing fluids may negatively impact the shale gas production through reducing the nanopore structure and porosity of shale reservoir rocks.
Highlights
Shale gas, a new kind of unconventional resources, has drawn great interest in many countries over the past decade (Davies et al, 2014; Jarvie et al, 2007; Zou et al, 2010)
The slight changes in these minerals can be attributed to the sample heterogeneity and the renormalization of the remaining phases following the changes in carbonate minerals
The evolution of pore structure parameters of shale treated with slick water and crosslinked gel fracturing fluid for different time periods were examined by considering shale mineral composition, pore structure and porosity
Summary
A new kind of unconventional resources, has drawn great interest in many countries over the past decade (Davies et al, 2014; Jarvie et al, 2007; Zou et al, 2010). Shale gas exploration and development have been promoted in the Sichuan Basin of China and constructed the Jiaoshiba, Changning, Weiyuan and Zhaotong four marine shale gas fields (Chen et al, 2015; Tian et al, 2013; Zou et al, 2010). The shale gas field in the Jiaoshiba area of Chongqing is the first commercial zone of shale gas development in China, with a recoverable resource volume of nearly 2 Â 1012 m3 (Chen et al, 2015; Yang et al, 2016). Fracturing fluid is one of the most important components of hydraulic stimulation and plays a key role in creating complex conductive fracture networks for gas to flow into the wellbore (Barati and Liang, 2014). The crosslinked gel systems may reduce the desired fracture complexity of shale (Wang and Elsworth, 2018)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
