Zonal isolation using elastic memory foam

1. A method for zonal isolation of an oil or gas well borehole, said method comprising:

forming an elastic memory foam expansion element on a base element, said foam expansion element having an original outer diameter larger than a selected borehole diameter;

raising said foam expansion element to its transition temperature;

radially compressing said foam expansion element to an interim outer diameter smaller than said selected borehole diameter;

cooling said compressed foam expansion element below its transition temperature;

running said compressed foam expansion element into a borehole on said base element; and

raising said foam expansion element to its transition temperature, to thereby radially expand said foam expansion element to seal between said base element and said borehole.

2. The method recited in claim 1 , further comprising:

forming said foam expansion element on a hollow mandrel;

attaching said hollow mandrel to said base element; and

radially expanding said hollow mandrel.

3. The method recited in claim 2 , wherein said radial expansion of said hollow mandrel is employed prior to said radial expansion of said foam expansion element.

4. The method recited in claim 2 , wherein said radial expansion of said hollow mandrel is employed during said radial expansion of said foam expansion element.

5. The method recited in claim 2 , wherein said radial expansion of said hollow mandrel is employed after said radial expansion of said foam expansion element.

6. The method recited in claim 2 , further comprising:

anchoring a hydro-mechanical expander within said base element; and

activating said hydro-mechanical expander to force a conical pig through said hollow mandrel, to achieve said radial expansion of said hollow mandrel.

7. The method recited in claim 2 , further comprising:

lowering a conical pig through said base element on a work string; and

forcing said conical pig through said hollow mandrel with said work string, to achieve said radial expansion of said hollow mandrel.

8. The method recited in claim 7 , wherein said conical pig is pushed through said hollow mandrel.

9. The method recited in claim 7 , wherein said conical pig is pulled through said hollow mandrel.

10. The method recited in claim 2 , further comprising:

pumping a conical pig through said base element with fluid pressure; and

forcing said conical pig through said hollow mandrel with said fluid pressure, to achieve said radial expansion of said hollow mandrel.

11. A packer for zonal isolation of an oil or gas well borehole, said packer comprising:

a mandrel; and

a substantially cylindrical expansion element formed on said mandrel, said expansion element being formed of elastic memory foam, said expansion element having first and second stable states;

wherein said foam expansion element in said first stable state has an outer diameter larger than a selected diameter;

wherein said expansion element is convertible to said second stable state by being raised to its transition temperature, compressed to an outer diameter smaller than said selected diameter, then cooled below its transition temperature;

wherein said expansion element is convertible back to said first stable state by again being raised to its transition temperature; and

wherein said elastic memory foam is formulated to have said transition temperature below an anticipated downhole temperature at a selected depth in a borehole, and said selected diameter is a diameter of said borehole.