ACOUSTIC EMISSION CHARACTERISTICS OF TIGHT SANDSTONE DUR-ING FAILURE PROCESSES WITH DIFFERENT CONFINING PRESSURES

Revealing the fracture mechanism of tight sandstone has important guiding significance for the fracturing design of tight oil and gas reservoir and the reconstruction of fracture network. This paper carries out the conventional triaxial compression tests of tight sandstone at different confining pressures. The rock samples are obtained from the Chang-6 reservoir of Yanchang Formation of the Ordos Basin. The influence of confining pressure on the mechanical properties of rock is analyzed. The fracture process of sample is studied by acoustic emission localization technique. The characteristics of acoustic emission location events and the space-time evolution of acoustic emission signals under different confining pressures are analyzed. In addition, CT scan is performed on the sample after rupture. The internal fracture characteristics of samples are observed based on CT slice images. The conclusions include the following. (1) The space-time evolution of acoustic emission is mainly expressed in the compaction stage under different confining pressures. With the increase of confining pressure, main acoustic emission events are postponed. (2) The effect of confining pressure on accumulative count is mainly manifested in the compaction stage. The accumulative count shows a similar trend on the other stage. Under different confining pressures, the moment when accumulative count increases rapidly can be as a sign of rock fracture. (3) With the increase of confining pressure, the fractured phenomena tends to simple. The complex phenomena dominated by tensile fracture gradually change into a single shear fracture. (4) CT scanning section directly reflects the fracture configuration of the sample. The whole fracture configuration of the sample is consistent with the acoustic emission location. Based on the acoustic emission location, the crack distribution and the interaction process of the crack are further described. The fracture process of sample is studied with acoustic emission technique and CT scanning technique, which is significant for investigating rock mass failure and instability mechanism.