A Comparative Study on Fracture Characteristics of the Red Sandstone under Water and Nitrogen Gas Fracturing

Abstract

Because of the disadvantages in fracturing with the water-base fracturing fluids and the development of reservoir reconstruction technology, nonaqueous fracturing fluid plays a more and more important role in the worldwide exploitation of unconventional natural gas. In this paper, the fracturing experiments of the red sandstone by using water and nitrogen gas are firstly carried out, and the breakdown pressures and failure patterns of the red sandstone specimens under different fracturing fluids are compared.en, based on the governing equations, the fracturing experiments with water and nitrogen gas are modeled by using a finite element method software-COMSOL Multiphysics. e conclusions can be obtained as follows: (1) e breakdown pressure of the nitrogen gas fracturing is 60% that of the water fracturing. e ultralow viscosity property of nitrogen gas is the reason for this phenomenon. (2) Compared with the water fracturing, the nitrogen gas fracturing causes greater volumetric strain and a more complex fracture pattern in terms of the number, length, and width of the cracks. (3) e numerical results are close to the experimental data. It implies that numerical modeling in this study can be used as a tool for predicting the breakdown pressure and rupture time. (4) After a sensitive study based on the numerical modeling, it can be found that the loading rate will influence the seepage range which dominates the pore pressure distribution and affects the breakdown pressure for the water fracturing. However, for the nitrogen gas fracturing, the breakdown pressure almost does not change with the loading rate as the nitrogen gas can easily penetrate the specimen from the radial direction.

Comparative Experimental Study of Fracture Mechanisms and Characteristics of Coal-like Materials under Quasi-Static and High-Pressure Air Blasting Fracturing

“…Numerous experimental studies have been conducted to investigate the mechanism and effect of high-pressure air fracturing on unconventional reservoirs. Zhao et al and Gao et al, respectively, compared the fracture pressure and damage mode of unconventional reservoirs under hydraulic fracturing and air/GN 2 fracturing. , The results showed that the low viscosity of air/GN 2 made the fractured rock samples form more complex crack surfaces, and air/GN 2 fracturing has a slower pressure decay after crack initiation, which is more conducive to crack extension, proving the feasibility and advantages of air quasi-static fracturing. Compared with air quasi-static fracturing, air blasting fracturing exhibits an extremely high pressure rise rate.…”

An Experimental Study of Seepage Properties in Crushed Sandstone and Mudstone

“…Many scholars have studied the mechanics and the prediction and the control measures of water inrush [12][13][14][15]. Bukowski [16] proposed a risk assessment method to classify mine shafts according to the risk of water inrush.…”