Experimental and numerical studies for determining the mode I critical stress intensity factor using thick-walled hollow cylindrical marly specimens

In the oil industry, hydraulic fracture is used for enhancing oil recovery in the case where the recovery yield has reduced due to long-term extraction or when the rocks around the oil well have low permeability. Since the notches are opened in tensile mode in the hydraulic fracture operation, only the mode I critical stress intensity factor (critical SIF) was investigated. The aim of the present study was to examine the effect of three important parameters including the notch length and width and confining pressure on the mode I critical SIF using a thick-walled hollow cylindrical marly specimen. The oil well environment was simulated in the laboratory. The marly specimen was prepared from the Bangestan Formation in southern and southwestern Iran. To perform the tests, two artificial symmetrical notches with certain dimensions were created in specimens with an outer diameter (OD) of 73 mm, an inner diameter (ID) of 25 mm, and a height of 150 mm. A triaxial stress was applied on the specimen and the pressure required for the propagation of the artificial notches was measured. Three tests were conducted to investigate the effect of each parameter on the mode I critical SIF. The experimental critical SIF was compared with the average critical SIF obtained from ABAQUS and ANSYS. It was found that the mode I critical SIF decreased with increasing in the notch width and increased with increasing in the notch length. The critical SIF nonlinearly increased with increasing in confining pressure.