FRACTURE RESISTANCE ANALYSIS ON THE CAP ROCK OF THE SAND LENS RESERVOIR DUE TO CARBON DIOXIDE INJECTION AND STORAGE

Injecting the CO2 into deep underground formations with the appropriate closure for isolated storage has been recognized as a possible effective technical approach in reducing CO2 emissions. The sand lens reservoir trap has a good structure and reservoir properties for the storage. The sand lens reservoirs with depletion of oil and gas are better CO2 geological storage boxes. Based on the pennyshaped crack model and the hydraulic fracturing principle，the sand lens reservoir of horizontal occurrence is simplified as a type-I pennyshaped crack of the cap rock. It is due to the fact that the thickness and horizontal distribution length of the reservoir are much smaller than the global cap rock scale. The cap rock fracture resistance of the storage box is analyzed from the view of rock fracture mechanics. The stress intensity factor of the pennyshaped crack tip (corresponding to the tip of sand lens reservoir) for the cap rock is calculated by the superposition principle. And then the fracture mechanics criteria (K=KIC) and the critical effective compressive stress criteria (P=PC) are concluded as the basic principle to evaluate the fracture resistance of the cap rock of the sand lens reservoir. The findings in the paper can provide a new way for the evaluation of cap rock fracture resistance capability of sand lens reservoir.