Abstract: Because the multiple continuous media model couldn’t describe the flow process between large scale cave and
stratum effectively，new well-test interpretation model of fracture-cavity type reservoir need to be established to study the fluid
flow rules of heterogeneous fracture-cavity type reservoir. The cave is simplified as an equal-potential body with equal internal
pressure anywhere，and the fluid flow outside of cave conforms to Darcy law. The fracture-cavity type reservoir mathematical
model is established based on the cave system mass conservation. The cave system pressure and wellbore pressure are calculated
by direct boundary element method. The cave pressure derivative curve and wellbore pressure and pressure derivative curve in
double-log axes are plot afterwards. The research shows that：the large scale cave bears an earlier-upward and later downward
characteristics in wellbore pressure derivative curve in double-log axes is. The larger cave radius induces larger upward and
downward scale；and the earlier cave distance from well induces the upward time. The smaller cave distance from well with
same radius induces larger peak value of cave pressure derivative；and the bigger cave radius with same distance from well
induces smaller peak value of cave pressure derivative.

Key words: fracture-cavity type reservoir, wellbore pressure, equal-potential body, cave system pressure, boundary elementmethod