ASSESSMENT OF FRACTURE BREAKDOWN PRESSURE IN LABORATORY EXPERIMENTS ON HYDRAULIC FRACTURING

Abstract

Hydraulic fracturing is one of the main ways to increase the flow rate of an oil/gas field. There are methods in which hydraulic fracturing is used to study the stress-strain state of the reservoir being developed. This work was devoted to assessing the correctness of one of these methods, based on known fracture breakdown pressures, using laboratory experiments. Some poroelastic effects are not taken into account in the standard methods of determining the stress-strain state. In the paper, it was proposed to adjust the existing formula for determining the fracture breakdown pressure taking into account the backstress effect. This effect consists in the additional influence of the rupture fluid, which has filtered out from the well into the well surrounding rock mass, on the effective stresses acting on the borehole wall. As part of the work, theoretical estimates of the fracture breakdown pressure were made, which were compared with experimental fracture breakdown pressures. As a result of the data analysis, it was revealed that the critical stress on the wall of the well in laboratory experiments is achieved somewhat later due to the presence of the backstress effect, which made it possible to refine the existing formula for estimating the fracture breakdown pressure.