Not realistic. A properly set charge could seal off the pipe a thousand or so feet down (after drilling to that level). But a large explosion will just fracture the rock and cause oil to leak through cracked rock. A nuke would be even worse for shaping the explosion plus would irradiate stuff that would last for thousands of years unlike oil which will only be around a few years at the most.
They know the geology of the area. Pick an unpermable oil layer and nuke below that. On irradiating stuff, you don’t know what you are talking about.