Refracturing is currently one of the most used methods to rejuvenate productivity of existing wells in low-permeability reservoirs in China. Different refracturing strategies have been conducted for vertical wells in a tight conglomerate reservoir in the Xinjiang. However

the underlying mechanisms are still unclear. By establishing the geomechanical model

the mechanism model of pore pressure inducing stress change based on the finite element method and the numerical model of unstructured reservoir

the researches on the fracture geometry of refracturing and the effect of different refracturing methods have been carried out. The results are as follows. Compared with the initial fracturing and conventional refracturing

the fracture geometry changes significantly after the volume refracturing. The azimuth of the in-situ stress before and after production does not change significantly

but the changes in pore pressure and in-situ stresses have a great impact on the geometry of hydraulic fractures. For the layers that have been perforated and produced

due to the strong energy loss

the propagation of fracture is more difficult

resulting in short fracture length and wide fracture width. In the case of adding new perforation in un-developed layers

as the formation can provide enough energy

it is easier to propagate fractures. The wells which are at the higher place of the new perforation layers have better productivity after the volume refracturing. The timing of refracturing also has a significant impact on oil production. A proper choice of refracturing time can effectively improve the well productivity.