Old well plugging method for constructing underground gas storage by depleted oil-gas reservoir

Abstract

Disclosed is an old well plugging method for constructing an underground gas storage by a depleted oil-gas reservoir. In order to prevent natural gas injected into the gas storage from channeling to a position close to an old well borehole along a gas reservoir, or vertically migrating along a first interface and a second interface of an oil well cement ring or channeling into a shaft along a perforated hole and migrating towards a non-gas-storage layer and a wellhead, the gas reservoir is plugged by a high-pressure squeezing process, a multi-stage cement plug is driven into the shaft to plug the shaft, and the length of a continuous cement plug above a top boundary of the gas reservoir is larger than or equal to 300m. If the top of cement above the top boundary of the gas reservoir is larger than 200m and a continuous cement bond section below a cap rock of the top boundary of the gas reservoir is larger than 25m, the continuous cement plug can be directly injected in a sectioned manner. If the top of cement above the top boundary of the gas reservoir is smaller than 200m and the continuous cement bond section below the cap rock of the top boundary of the gas reservoir is smaller than 25m, the cap rock above the top boundary of the gas reservoir is forged and milled by a casing, the forging and milling length is larger than or equal to 30m, and the continuous cement plug is injected in a sectioned manner after forging and milling. The old well plugging method has the advantage that the natural gas entering the casing is effectively prevented from migrating towards the non-gas-storage layer and the wellhead.

Description

technical field [0001] The invention relates to a technology for constructing an underground gas storage of a depleted oil and gas reservoir, in particular to a method for plugging an old well of an underground gas storage for a depleted oil and gas reservoir. Background technique [0002] The types of underground gas storage generally include rock salt caverns, depleted oil fields, underground aquifers, and depleted oil and gas fields. [0003] Salt cavern underground gas storage has a small storage capacity; salt layer creep can easily cause casing damage, resulting in a large volume loss; brine discharge and leakage may cause gas loss; There are certain risks in terms of sealing and stability. [0004] The gas storage rebuilt in the depleted oilfield has unrecoverable residual oil in the oil reservoir, and a certain amount of crude oil is carried in the recovered gas, which requires special treatment, which limits its application. [0005] Because there is no gas in the...

AI Technical Summary

Problems solved by technology

The natural gas injected into the underground gas storage transformed from the depleted oil and gas reservoir will channel along the gas reservoir to the vicinity of the old wellbore, or migrate up and down along the first and second interfaces of the cement sheath, or along the jet Holes enter the wellbore and migrate to non-gas storage layers and wellheads, which poses a safety risk to the gas storage