Abstract: Since it is not possible to perform multiple expansion and patching operations in lower parts of the well with casing damage,a variable-diameter expandable cone has been designed to perform multiple patching operations in wells with casing damage. It is accomplished through the delivery of tools in minor diameters and expansion for patching operations in large diameters. In addition to structure design of the variable-diameter expandable cone,mechanical calculation model and dynamic calculation model for closure of the cone have been established to highlight functions among expansion,propulsion,conic angle and friction coefficients,as well as the function among propulsion,constriction and friction coefficients. Calculation results showed that expansion force is 1.53 times of propulsion. With the end friction coefficient increased from 0.1 to 0.4,propulsion increased 8.8 kN,and with the end friction coefficient increased from 0.5 to 0.8,propulsion increased 19.0 kN,the maximum stress on expandable cone was determined to be 454 MPa. Experimental tests of the prototype of the expandable cone demonstrated that the innovative tool has rational structural design with initiation pressures of 3-5 MPa and complete closure pressure of 52 MPa. The maximum OD of the expandable cone may increase from 188.0 mm to 220.0 mm with expansion rate up to 17.02%,which is identical to that of the conventional expandable cone. Research results showed that expansion forces present linear increase with the increases in propulsion. With the capacity for delivery in minor diameter and expansion to larger diameters,the expandable cone can further reduce closure pressure. Generally speaking,this application of the expandable cone has bright prospects.