Method for treating a tar sand reservoir to enhance petroleum production by cyclic steam stimulation

A method for conditioning the virgin drainage area of a tar sand formation that is penetrated by a well for enhanced petroleum production by cyclic steam stimulation is described. The method comprises fracturing the drainage area by injection of liquid carbon dioxide. While carbon dioxide is still in place within the formation, steam is injected into the formation. After a suitable soaking period, the well is opened to production. This method achieves better petroleum recovery than conventional huff-puff steam stimulation techniques.