The invention belongs to the field of air driving exploitation of reservoirs and particularly relates to a
system for determining a critical pressure gradient of foams generated at a permeability
mutation site. The
system comprises a sand filling
pipe, a liquid supplying device, an air supplying device, a data collection device and an observation device, wherein the data collection device is connected with the sand filling
pipe; the sand filling
pipe is provided with an injection end and a flow-out end, two sections of filling mediums with different grain diameters are arranged in the sand filling pipe, the filling mediums with relatively small grain diameters are used for filling close to the injection end to form a front sand filling section, the filling mediums with relatively large grain diameters are used for filling close to the flow-out end to form a rear sand filling section, the sand filling pipe is a transparent tempered glass pipe, and the filling mediums are
black glass beads; and the observation device comprises a
microscope and a computer, the
microscope is arranged opposite to the outer circumferential surface of the sand filling pipe, the computer is connected withthe
microscope, and a camera is arranged on the microscope. According to the
system, the critical pressure gradient of the foams at the permeability
mutation site can be determined, and the foams arearranged in a
porous medium environment to be researched, so that the influences caused by the
mutation of the permeability in a heterogeneous reservoir to the generation of the foams are truly reflected.