Research on the Mechanism of Fracturing Fluid's Influence on Mechanical Properties of Sandstone

ABSTRACT Fracturing fluid is the main cause of reservoir damage during hydraulic fracturing. Fracturing fluid will change the mechanical properties of reservoir rock, and the effect of proppant-propping hydraulic fractures will be affected. To study the changes and internal mechanism of sandstone mechanical properties after guar gum fracturing fluid damage, triaxial compression experiments, core flow experiments, scanning electron microscopy, and nuclear magnetic resonance tests were carried out on sandstone cores before and after damage. The results showed that: (1) The compressive strength and elastic modulus of sandstone decreased after guar gum fracturing fluid damage, which was caused by the increase of the average pore radius of the rock and the weakening of the interaction between particles. (2) The changes in sandstone microstructure after fracturing fluid damage are as follows: rock particle migration, fracturing fluid macromolecule residues, and the proportion of micro-pores decrease (11%). (3) Tight sandstone is more sensitive to guar gum fracturing fluid, and the lower the initial permeability of sandstone, the greater the decrease in compressive strength and elastic modulus after damage. (4) The change of rock mechanical properties is positively correlated with the range of permeability change. It is of great significance to consider mechanical properties as a factor in the study of fracturing fluid damage. INTRODUCTION Unconventional tight sandstone gas has become a natural replacement area for natural gas exploration and development. According to the fourth national oil and gas resource evaluation results, in the tight gas field, the currently proven recoverable reserves are 3.96×1012m3, accounting for 33% of the total proven resources and the remaining recoverable resources are 6.97×1012m3. From the distribution of remaining resources, the future tight gas exploration areas are still concentrated in the Ordos and Sichuan Basins (Zheng Min, 2019). The low-permeability tight gas reservoirs in the Ordos Basin have large reserves. However, they have poor physical properties, substantial heterogeneity, low reserves, and significant differences, and it is not easy to achieve long-term stable production and profitable development of gas reservoirs (Cheng Lihua, 2020).