Experimental investigation of the fracture initiation and propagation for sandstone hydraulic fracturing under the effect of evenly distributed pore pressure

Pore pressure is disregarded in traditional laboratory rock hydraulic fracturing experiments, and the effect of pore pressure is not clear. An integrated experiment for seepage and hydrofracturing was established and used to perform sandstone hydraulic fracturing experiments under an initial evenly distributed pore pressure. The experimental results show that there is a positive correlation between the breakdown pressure and the pore pressure at the initiation stage. The data fitting results show that the breakdown pressure and pore pressure follow a linear growth trend. As the pore pressure increases, the acoustic emission energy at the moment of borehole wall fracturing correspondingly increases. After borehole wall fracturing, the reduced magnitude of the pumping pressure also increases, indicating that the initial rupture range is positively correlated with pore pressure. During fracturing propagation, the propagation range and opening of the fracture increase as the initial pore pressure increases within the same pumping time. During hydraulic fracturing, a pore pressure gradient is generated on both sides of the mineral particles. When the tensile stress or shear stress induced by the pore pressure gradient reaches the ultimate strength of the mineral particle bonding surface, the particle bonding surface breaks and opens. This experimental process is more similar to the actual hydraulic fracturing process of oil and gas reservoirs. These results provide a more comprehensive theoretical basis for resolving technical problems of unconventional oil and gas resource exploitation.

Automated summary

Pore pressure is an important factor in sandstone hydraulic fracturing experiments. The experimental results show that there is a positive correlation between breakdown pressure and pore pressure. As pore pressure increases, the energy released during fracturing and the initial rupture range also increase. The results provide a theoretical basis for unconventional oil and gas resource exploitation.