Damage Assessment of Fracturing Fluid in Continental Sedimentary Tight Reservoir Based on NMR Technology

Abstract Nowadays, fracturing technology (FT) is a key stimulation technology to develop tight sandstone reservoirs. It is of great significance to quantitatively evaluate the damage caused by the fracturing fluid to various pore sizes under different operating conditions. In this paper, NMR technology is used to quantitatively evaluate the damage caused by the fracturing fluid to various pores and throats with different sizes under various operating conditions in order to investigate the effect of mass fraction, fracturing fluid type, pore size and clay content on the formation damage. It is obtained that the degree of formation damage caused by guar gum fracturing fluid (25.09 %~44.75 %) was significantly greater than that associated with slippery water fracturing fluid (11.74 % ~ 26.82 %). The damage scale of the guar gum fracturing fluid was 0.10~1664.18 ms, and that of the slippery water was 0.41~496.59 ms. Guanidine fracturing fluid mainly damaged the macropores (>10 ms) while the slippery water fracturing fluid mainly damaged the mesopores (1.00~10.00 ms). To reduce the formation damage, the best mass fraction for the guar gum and slippery water fracturing fluids were obtained at 0.2 and 0.5 %, respectively. The degree of formation damage had a positive correlation with the clay content and mass fraction. The more clay content and mass fraction, the greater the extent of formation damage associated with the fracturing fluid. Introduction The unconventional oil and gas resources associated with the tight sandstone reservoirs have attracted much attention recently and as such, methods to develop these unconventional resources have been the topic of academic and industry research (Rebekah et al., 2021; Yu et al., 2021; Wang et al., 2019; Zachary et al., 2015; McGlade et al., 2012;). These unconventional oil and gas resources could become a stable source of energy provided that sustainable technological advances in field development will be introduced. There are some inherent complexities associated with developing these unconventional plays such as strong heterogeneity, poor percolation capacity, and complex pore structure, all of which lead to low single well productivity and great field development difficulty (Pang et al., 2021; Wang et al., 2019; Li et al., 2018; Li et al., 2016; Zou et al., 2012). In view of such difficulties, hydraulic fracturing is a key technology for developing tight unconventional plays in which fracturing fluid is injected into the reservoir under constant applied pressure.