of this invention is crumb rubber crumb rubber generally comprises rubber derived from recycled tires or scrap material from the manufacture of tires crumb rubber particles are generally of u215c inch or less in size in the practice of the invention the crumb rubber should have a mixture of particle sizes ranging of from 1 to 400 microns preferably 20 to 400 microns in the preferred embodiment the material should include particles of varying diameters within the range stated above crumb rubber can be prepared several different ways in the first method whole tires are cryogenically frozen and then shattered in a hammer mill to break down the tire into the desired particle sizes and to remove the steel and fibers from the tire a second method involves physically tearing the tire apart and removing the unwanted steel and fibers in this process the tire is continuously milled until the desired particle sizes are obtained another source of crumb rubber is the bushings that remain as the tire is manufactured or remanufactured one key feature of crumb rubber that makes it useful in the practice of the invention is its ability to expand up to 140 of its original size when exposed to hydrocarbon fluids and temperatures as shown in the examples below when the elastomer particles are exposed to hydrocarbon fluids and temperatures typically encountered in a well 200 u00b0 f to 300 u00b0 f the particles expand to over 140 of their original size the amount of expansion is dependent upon the hydrocarbon used and the temperature in the well the expansion of the elastomer is not immediate often taking several hours before a.