The amount of CO2 being used as fracturing fluid has been more than 30,000 tons at Changqing oilfield in 2022, Which above several times over the sum of the last five years. A serials of experiments and experimental analyses devoted to the CO2 fracturing mechanism were conducted in order to provide some advices for the CO2 fracturing treatment design and improve the well performance. An experimental analysis for the CO2-core leakoff experiments was made in which compares the leakoff characteristics under the liquid and gas phase of CO2. The plot for the square-root time vs.leakoff rate was got. Two sets of CO2 fracturing physical simulation experiments on the cores of 762 × 762 × 914.4mm were carried out, which compares the fracture’s geometry and size with the slick water experiments’ results. The mechanism that lead to the rock breakdown pressures’ decreasing with CO2 fluid was researched based on the Elasticity mechanics and the Fracture Mechanics theory. The results show that CO2 has a very high leakoff rate within the core which leads to a lower rock breakdown pressure value and a smaller fracture size and an excellent capacity for complicating the rock’s fractures than the conventional fracturing fluid.
Keywords CO2, CO2 fracturing, CO2 leakoff, leakoff experiment, fracturing simulation, physical fracturing experiment