The wellbore collapse on sandstone formation during well test with matrix acidizing treatment

Matrix acidizing treatment is a useful method to reduce skin factor, which can relieve pollution near wellbore on the sandstone formation. The collapse of wellbore would cause failure of the well test after acidizing treatment. The authors studied changes of rock characteristics by acidizing experiments. In those experiments, Young's modulus, cohesion, and internal friction angle reduce with time, which are fitted by numerical method. A model of the changing Young's modulus during acidizing treatment is built based on damage mechanism. Because Young's modulus changed, stress distribution around wellbore would change, which is different from that of conventional models. So new models are built to describe the stress around wellbore with matrix acidizing treatment on brittle and plastic rock. Based on the changed rock characteristics and redistributed stress, models of collapse pressure are built for brittle and plastic formations, respectively. Results indicate collapse pressure ascends as the effective acidizing radius is extending. For brittle rock, collapse pressure is higher than that of plastic rock on the same conditions.