Experimental study on initiation and propagation of hydraulic fractures in stratified shale oil reservoirs

The bedding planes of the Gulong shale oil reservoir in Daqing, China are extremely developed, which causes the hydraulic fractures to extend excessively in the horizontal direction while their longitudinal propagation is limited. In order to improve the fracturing effect, there is an urgent need to study the propagation law of hydraulic fracture in stratified shale oil reservoirs. Therefore, according to the characteristics of Gulong high bedding density reservoir and the actual fracturing process, the corresponding true triaxial hydraulic fracturing physical simulation test is designed in this study. The test results show that the higher the bedding density, the weaker the longitudinal propagation ability of hydraulic fractures, and the fracture height decreases by 29.6% with the increase of bedding density. The strength of bedding directly affects the opening degree. When the bedding strength is enhanced, the opening degree of bedding is significantly reduced, and the fracture height is increased by nearly 2.8 times. Controlling the viscosity of fracturing fluid can inhibit the opening of bedding, and increasing the viscosity can reduce the opening area of bedding by 9.6%. Controlling the displacement is beneficial in promoting the opening of multiple bedding, and increasing the displacement can increase the opening area of bedding by 48.3%. The study results can provide some theoretical and technical support for hydraulic fracturing process optimization of shale oil reservoirs with stratified development.