Method and apparatus for isolating and treating subsurface stratas

Apparatus by which a production formation within a wellbore can be isolated and treated by freezing the well fluids and adjacent strata at spaced locations above and below said production formation so that treatment fluid can subsequently be pumped into said production formation, said apparatus comprises;

• an upper and a lower vessel within which nitrogen or the like can be stored;
• a tubing string, a vent assembly;
• said tubing string extends from the surface of the earth, downhole to proximity of the production formation, said vent assembly being formed on the lower marginal end of said tubing string, said upper and lower vessels being connected to the lower marginal end of said tubing string with said vent assembly being located between said vessels;
• means by which said vent assembly can be moved from a closed to an opened position by a wire line fishing tool, thereby enabling the interior of the tubing string to remain dry until the vent assembly is moved to the open position;
• means insulating said vessels such that heat transfer thereto is minimized, means for removing said means insulating said vessels such that heat transfer thereto is maximized;
• each said vessel having a vapor space and a liquid space when filled with liquid nitrogen or the like;
• pressure regulator means by which the vapor space of each vessel is vented into the interior of said tubing string such that the vapor pressure of the liquid contained within the vessels is maintained at a predetermined value which is below the breaking strength of the vessel, while the vapors are vented up the interior of the tubing string and into the atmosphere;
• whereby, said vessels may be lowered on the end of the tubing string and positioned to straddle the production formation to be treated, said insulators are moved to expose the vessels to well fluid while said nitrogen is vaporized and vented to atmosphere to reduce the temperature of the immediate area and thereby form spaced plugs, and said vent assembly can thereafter be moved to the opened position to enable treatment fluid to be pumped down the tubing string and laterally from the tubing string into the production formation.

In a cased borehole having an upper and lower zone communicated by a flow passageway in proximity of and externally of the casing, the method of cementing off the flow passageway communicating one zone with the other, comprising the steps of:

• attaching an insulated vessel to a tubing string by using a vent assembly, filling the vessel with a liquid having a high vapor pressure, placing a packer on the tubing string uphole of the vent assembly, and running the vessel into the borehole and positioning the vessel at a location between the upper and lower zones;
• removing the insulation from the vessel so that the exterior thereof makes intimate contact with any fluid contained within the wellbore, thereby causing heat in proximity of the vessel to be absorbed by the vaporizing action of the liquid contained therewithin;
• continuing to remove heat until the well fluid and adjacent strata is frozen to form a plug, thereby temporarily preventing flow from one of said upper and lower zones to the other;
• perforating the casing at a location above the frozen area and below said upper zone;
• opening the vent string and pumping cementitious material down the tubing string, through the vent assembly, into the annulus between the tubing and casing, through the perforations, and into the passageway which communicate the upper and lower zones, thereby filling the passageway with cementitious material to prevent subsequent flow therethrough;
• removing the vessel along with the packer and vent string from the borehole after the frozen well fluid has thawed.