The present invention provides a method for maintaining the mechanical integrity and for maximizing the chemical integrity of a core sample during transport from a subterranean formation to the surface. The method involves cutting and encapsulating a core sample with an encapsulating material that increases in viscosity or even solidifies, at temperatures slightly lower than those expected downhole, or relatively early in the transport process. A preferred encapsulating material contains at least one polyglycol or chemically modified polyglycol from the oxyalkylene polymer family. The specific formulation of the encapsulating material differs depending upon the expected downhole conditions. For example, the encapsulating material can include a thickener, a nucleating agent, and a water swellable material or another inert material that is capable of sealing the core sample against water. A preferred nucleating agent would serve both as a heat transfer agent and a crystallization trigger, and therefore would speed up the rate at which the encapsulating material would solidify or increase in viscosity, particularly downhole. The encapsulating material should either solidify or increase in viscosity enough to protect the mechanical integrity and maximize the chemical integrity of the core sample for analysis at the surface. The chemical integrity of the core sample can be further maximized by using the present invention in conjunction with a pressure core barrel.
Pierre E. Collee;William A. Mallow;Steven R. Radford