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A method for rupturing a glass disc in a well completion tool located downhole in a section of production tubing includes providing a wellhead isolation tool, or tree saver, to isolate the wellhead Christmas tree, adding a pressurized fluid to the tubing/casing annulus and pumping a disc rupturing f

A method for rupturing a glass disc in a well completion tool located downhole in a section of production tubing includes providing a wellhead isolation tool, or tree saver, to isolate the wellhead Christmas tree, adding a pressurized fluid to the tubing/casing annulus and pumping a disc rupturing fluid into the production tubing via the tree saver until the disc is ruptured. Following rupture, the pump can be rapidly stopped, or slowed, and started to create a water hammer effect that removes any glass shards remaining in the disc holder.

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What is claimed is: 1. A method for rupturing a glass disc during the completion of a well, the glass disc being positioned in a section of downhole production tubing in the well, the tubing being positioned in a casing extending from the wellhead to a position below the production tubing section c

What is claimed is: 1. A method for rupturing a glass disc during the completion of a well, the glass disc being positioned in a section of downhole production tubing in the well, the tubing being positioned in a casing extending from the wellhead to a position below the production tubing section containing the glass disc, the wellhead being fitted with a Christmas tree for controlling hydrocarbon production, and a wellhead isolation tool attached to the wellhead downstream of the Christmas tree, the method comprising the steps of: a. adjusting the wellhead isolation tool to isolate the Christmas tree from downhole hydraulic pressure forces; b. introducing a pressurized rupturing fluid into a section of the production tubing below the wellhead isolation tool that is in communication with the glass disc; c. introducing a substantially incompressible fluid into the annular space between the production tubing and the surrounding casing; and d. increasing the hydrostatic pressure on the rupturing fluid in the production tubing to a level that is sufficient to rupture the disc while simultaneously maintaining the pressure of the fluid in the annular space at a predetermined value in order to prevent the tubing from rupturing and/or collapsing as a result of the pressure differential. 2. The method of claim 1, further comprising: e. shutting down pumping after the rupturing of the glass disc; f. releasing the pressure on the rupturing fluid in the tubing though the wellhead isolation tool; and g. bleeding the tubing/casing annulus pressure. 3. The method of claim 1, wherein tool stems are extended down below a tubing hanger of the wellhead during the application of the pressurized rupturing fluid. 4. The method of claim 1, wherein a predetermined minimum pressure is maintained in the annular space during the pressurizing of step (d). 5. The method of claim 1, wherein the rupturing fluid is pressurized by a high pressure pump connected to the wellhead isolation tool. 6. The method of claim 1, further comprising alternately starting and stopping fluid injections into the tubing to create a water hammer to thereby flush any shards of the glass disc from its holder. 7. The method of claim 2, wherein the pumping pressure at which the glass disc is ruptured is determined by the following equation: pumping pressure to be applied at the wellhead=reservoir pressure at the glass disc+ΔP−hydrostatic pressure exerted by the wellbore completion fluid above the disc,   (1) where ΔP is a differential pressure at which the glass disc is ruptured in a laboratory test. 8. The method of claim 5, which includes the steps of pressure-testing surface connections to the unit with water to the maximum predetermined pumping pressure and displacing the water with a non-aqueous rupturing fluid prior to pressurizing the tubing and the annular space. 9. The method of claim 1, wherein the pressure of the rupturing fluid in the tubing is raised gradually. 10. The method of claim 1 in which the same fluid is used to pressurize the tubing and the annular space. 11. The method of claim 10 in which the fluid is diesel oil. 12. The method of claim 1 in which the maximum value of the pressure maintained in the annular space is less than the pressure required to rupture the disc. 13. The method of claim 12 in which the pressure of the fluid in the annular space is from 300 to 700 psi. 14. The method of claim 1 which includes installing a rubber-to-metal seal to isolate the Christmas tree.