Extending behavior of hydraulic fracture when reaching formation interface

Stopping extension, extending along formation interface and directly penetrating into bounding layer are three possible reactions of fracture extension when hydraulic fractures reach formation interfaces. The three types of extending behavior are analyzed using rock fracture mechanics and three respective judging criterions are presented. Layered earth stress, layered rock mechanics parameters, formation interface effect, reservoir thickness and operating parameters are taken into consideration. This study indicates that there exists a critical fracture length when fracture extension stops. Hydraulic fractures will extend along formation interfaces or penetrate into bounding layers when fracture lengths are larger than the critical fracture length. The method to calculate critical fracture length is introduced. In the case of direct penetration into the bounding layer, the method to estimate hydraulic fracture height is presented based on superposition of stress intensity factors. A case study is also included to show the operability of our theory.