Method and apparatus for dual string well tree isolation

An apparatus for injecting fluids, gases, solid particles or mixtures thereof into a well having first and second production tubing strings, the fluids being injected through a dual string well tree which has first and second vertical passages therethrough respectively aligned with the first and second production tubing strings and has at least one valve for selectively closing each passage, the apparatus comprising:

• first and second isolation assemblies for injecting the fluids through the respective first and second vertical passages, each of the isolation assemblies including:
• (a) a high pressure tubing for insertion through a respective one of the vertical passages;
• (b) a high pressure valve connected to the high pressure tubing to selectively stop fluid flow through the high pressure tubing;
• (c) a first sealing device adapted to prevent passage of the fluids and gases from an exterior of the high pressure tubing and an interior of the vertical passage to atmosphere;
• (d) a second sealing device adapted to prevent passage of the fluids and gases from an interior of the high pressure tubing and an interior of the production tubing to the vertical passage when the high pressure tubing is inserted into the vertical passage;
• (e) a hold down mechanism for detachably securing the high pressure tubing and the high pressure valve to the dual string well tree;
• a swedge having an axial passage, adapted to be detachably mounted to the dual string well tree in alignment with the second vertical passage to extend the second vertical passage upwardly past the first high pressure valve when the high pressure valve is secured by the hold down mechanism, the second high pressure tubing being inserted into the second vertical passage from a top end of the swedge;
• a hydraulic cylinder having an extendable and retractable piston rod that is respectively and detachably connected to each of the first and second assemblies for inserting the first high pressure tubing into the first vertical passage and the second high pressure tubing into the second vertical passage;
• and
• at least two elongated hydraulic cylinder support rods fixable relative to the dual string well tree in a respective position parallel with and offset from the vertical passages respectively and adapted to support the hydraulic cylinder in axial alignment with the respective vertical passage, the support rods and the hydraulic cylinder being removable from the dual string well tree when each of the high pressure tubings is operatively inserted into a respective vertical passage.

A method of isolating a dual string well tree having first and second vertical passages, aligned respectively with first and second production tubing strings of an oil or gas well, from the effects of high pressure or corrosion caused by stimulation of the well, the method comprising steps of:

• (a) mounting a first isolation assembly having a high pressure tubing to the dual string well tree in alignment with the first vertical passage, and inserting the high pressure tubing through the vertical passage to an operative position in the first production tubing string to isolate fluids, gases, solid particles and mixtures injected therethrough from an interior of the first vertical passage;
• (b) securing the high pressure tubing of the first isolation assembly to the dual string well tree;
• (c) mounting a swedge having an axial passage to the dual string well tree, the axial passage being sealingly aligned with the second vertical passage and a top end of the swedge being vertically offset from a top of the first assembly;
• (d) mounting a second isolation assembly having a high pressure tubing to the swedge in alignment with the second vertical passage, and inserting the high pressure tubing through the swedge and the second vertical passage to an operative position in the second production tubing string to isolate fluids, gases, solid particles and mixtures injected therethrough from an interior of the second vertical passage;
• and
• (e) securing the high pressure tubing of the second assembly to the dual string well tree.