Experimental Study on the Characteristics of Fractures Created by Liquid Carbon Dioxide in Thin Interbed Shale Reservoirs

ABSTRACT: CO₂ fracturing has been pilot tested to improve the hydraulic fracture complexity of the near-well area in Jimsar thin interbedded shale reservoirs. However, the characteristics of hydraulic fractures created by CO₂ in this reservoir has not been studied systematically from experiment. Aiming at this, we conducted true triaxial fracturing experiments on the tight shale with thin interbedded bedding (from Jimsar formations) by using liquid CO₂. In the experiments, the effect of natural fracture, pump rate, and horizontal principle stress difference on fracture morphology was studied respectively. Also, the characteristics of fractures created by CO₂ was compared with water. The results show that the bedding planes of thin interbedded rock is easy to be opened by low viscosity of CO₂ and the vertical fractures intersecting with bedding planes build complex fracture network. When natural fractures exist in rock samples, the natural fractures are opened simultaneously with the bedding planes. Increase pump rate can enhance fracture complexity. Due to the ultra-low viscosity, strong penetration ability of liquid CO₂, and the weak bonding strength of the horizontal bedding planes, the horizontal principal stress difference has less effect on fracture propagation in the CO₂ fracturing experiment of bedding rich core samples.