The Supercritical CO₂ Fracturing Experimental Study on Fracture Initiation of Different Rocks

Supercritical carbon dioxide has been proposed as an anhydrous fracturing fluid to exploiting unconventional oil and gas, because it can well solve the problems such as water shortage, clay swelling and fluid backflow difficulties caused by traditional water-based fracturing fluid. However, based on the previous researches, the characteristic of fracture initiation on different lithology still need to be researched. In this work, fracturing experiment with different rocks were performed to investigate fracture initiation. The experimental results show that various rocks have different initiation pressure, but the initiation direction is roughly similar to be across the wellbore. The initiation pressure of different rocks is positively correlated with the strength of rocks. And the shape of crack is more complicated and the extension direction is more diverse as the increase of the breakdown pressure. Finally, the comparison of surface micro-morphology of different rocks before and after fracturing suggests that this process can extend the preexisting fractures and create some new and complex fractures. The micro-scale damage will be beneficial to the migration and accumulation of oil and gas in the reservoir. This experimental study can lay a certain foundation for the application of supercritical CO₂ fluid in oil and gas exploitation.