Construction method for replacing valve under pressure for liquid nitrogen freezing bridge plug

Abstract

The invention belongs to the technical field of exploration and development of oil-gas fields, and specifically provides a construction method for replacing a valve under pressure for a liquid nitrogen freezing bridge plug. The construction method comprises the following steps: digging a liquid storage pit in ground in the peripheral direction by taking a sleeve with a valve to be replaced as a center; marking a highest liquid level marker line on the sleeve in the liquid storage pit; establishing a steel tube framework on ground by taking a gas recovery well mouth of the valve to be replacedas the center; mounting a pedal on the steel tube framework; injecting liquid nitrogen into the liquid storage pit until the liquid level reaches the highest liquid level marker line; paving a thermalinsulation pad on the pedal; manufacturing a freezing bridge plug; replacing an invalid valve; sequentially dismounting the thermal insulation cushion, the pedal and the steel tube framework, openingthe liquid storage pit to volatilize liquid nitrogen therein, and backfilling earth into the liquid storage pit with liquid nitrogen completely volatized to accomplish the construction. The construction method solves the problems that a conventional freezing valve-replacing process is great in construction difficulty, is high in potential safety hazard, is low in freezing efficiency and the like,and has the characteristics of improving freezing efficiency, reducing operation time, and reducing operation cost.

Description

technical field [0001] The invention belongs to the technical field of oil and gas field exploration and development, and in particular relates to a construction method for replacing valves under pressure with liquid nitrogen frozen bridge plugs. Background technique [0002] After years of development, the process of replacing valves with frozen bridge plugs has become mature. It is basically finalized as digging a working pit around the wellhead, installing a ring-shaped freezing box around the surface casing, adding refrigerant, pre-freezing, making frozen bridge plugs, and replacing valves. A process, on the whole, the effect is not bad, but in the process of operation, there are still many disadvantages and hidden dangers, mainly concentrated in the first two links: first "digging the working pit around the wellhead": the original process requires digging around the wellhead Due to the impact of the wellhead equipment, the working square pit with a length, width and hei...

AI Technical Summary

Problems solved by technology

[0002] After years of development, the process of replacing valves with frozen bridge plugs has become mature. It is basically finalized as digging a working pit around the wellhead, installing a ring-shaped freezing box around the surface casing, adding refrigerant, pre-freezing, making frozen bridge plugs, and replacing valves. A process, on the whole, the effect is not bad, but in the process of operation, there are still many disadvantages and hidden dangers, mainly concentrated in the first two links: first "digging the working pit around the wellhead": the original process required digging around the wellhead Due to the influence of the wellhead equipment, the working square pit with a length, width and height of 2 meters is very difficult to construct on two sides. The excavation equipment is easy to collide with the wellhead gate, which poses a safety hazard

The second "install the ring-shaped freezing box around the surface casing": due to the limitation of the working pit space, the height of the ring-shaped freezing box is only 550mm, the thickness of the formed frozen bridge plug is less than 0.6 meters, and the effective volume of the frozen medium is only 0.15m 3 , the freezing efficiency is low; the ring-shaped freezing box is made of two semicircular metal boxes buckled outside the sleeve, with a rubber piece in the middle, and assembled with clamps and screw rods. Different specifications of sleeves require Processing freezer boxes of different sizes

The metal parts between the freezing box and the casing are hard-connected, and it is difficult to make it just right, so it often leaks when containing the freezing medium

The commonly used freezing medium is a mixture of dry ice and methanol, which is very slippery when it flows into the work pit. Methanol is corrosive and toxic, which affects personnel working in the work pit.

In addition, a large amount of carbon dioxide gas is easy to accumulate in the working pit, and it is easy to suffocate when adding freezing medium inside

Images