A method of operator controlled, selective full drainage of pumping liquid from a producing oil well downhole pipe string formed of end to end pipe sections and having a pump unit at the lower end thereof, said method comprising:
- attaching an elongated, tabular pipe section connection body to a pipe section at a lower part of the pipe string,
- said connection body having a sidewall with opposed inner and outer faces presenting a generally cylindrical interior having a selected internal diameter, said connection body being provided with a threaded opening extending through the sidewall between the inner and outer faces thereof;
- threading an integral, externally threaded pressure activated fitting into the threaded opening of the connection body sidewall to form a thread to thread, complemental, metal to metal liquid tight seal between the fitting and the sidewall, said fitting having a tubular housing which has wall structure presenting a central liquid discharge passage therethrough, said wall structure having a circular inner edge portion defining the pumping liquid entrance of the passage that is adjacent the inner face of the connection body, said circular inner edge portion of the wall structure being of a diameter approximately equal to the diameter of said passage,
- said fitting including a thin, metallic, frangible, shape-retaining rapture disc having an outer circular marginal portion welded to the inner circular edge of the wall structure defining said passage though the housing of the fitting,
- said disc being bulged inwardly of the passage to present opposed concave-convex surfaces with the concave surface thereof directly facing the interior of the connection body, said disc being provided with at least one line of weakness extending across the disc,
- said disc being of a thickness and having at least one line of weakness such that the disc thickness and line of weakness depth are correlated to impart a predetermined pumping liquid withstand pressure to the disc sufficient to withstand the pressure of pumping liquid normally contained ma particular length of pipe string when the pipe string is inserted in and extends along the length of the well casing, thereby preventing pumping liquid flow through the passage in the housing under normal production operating conditions,
- the disc thickness and the line of weakness depth being further correlated to reliably effect operator-actuated rupture of the disc when a predetermined pumping liquid activation pressure is applied to the pumping liquid in the pipe string;
- introducing pipe sections in successive order into the oil well to form said pipe string with the connection body and fitting therein located at an operator selected depth in the oil well;
- when it is desired to drain the pumping liquid from the downhole pipe string, selectively pressurizing the column of pumping liquid in the pipe string to said predetermined activation pressure to effect rupture of the disc along said at least one line of weakness as the disc petals formed thereby fold outwardly against and are confined by the passage defining wail structure of the housing;
- and
- successively pulling the pipe sections of the pipe string from the oil well at a rate permitting drainage of pumping liquid in the pipe string through the opening of the ruptured disc and the passage in the fitting into the oil well without significant overflow of pumping liquid in the pipe string onto the area surrounding the oil well.