A Gas Hydrate Replacement Method Combined with Injection of Hot Seawater to Enhance Methane Recovery and Carbon Dioxide Storage

Abstract

The invention belongs to the field of natural gas hydrate extraction, in particular to a natural gas hydrate replacement method for combining hot seawater injection methane extraction enhancement and carbon dioxide storage. The method comprises the steps that firstly, after well drilling is completed, hydrate reservoir pressure is reduced, and natural gas hydrate around a shaft is located in a metastable state; then the shaft is utilized for injecting carbon dioxide into a reservoir, and a replacement reaction occurs on a hydrate reservoir extraction shallow layer close to the shaft; the shaft is utilized for injecting carbon dioxide and hot seawater into the reservoir, dense carbon dioxide and methane mixed hydrate formed through the replacement reaction is decomposed, and methane in small holes of the hydrate incapable of being replaced is developed; finally, injection of the hot seawater is stopped, carbon dioxide is continuously injected into the reservoir, the carbon dioxide is migrated to a hydrate reservoir extraction deep layer, and more hydrate is promoted to be subjected to the replacement reaction. The aims of safely and efficiently extracting the hydrate and storing the carbon dioxide to relieve the greenhouse effect are achieved at the same time.

Description

technical field [0001] The invention belongs to the field of natural gas hydrate exploitation, and relates to a natural gas hydrate replacement method combining injection of hot seawater to enhance methane exploitation and carbon dioxide sequestration. Background technique [0002] Natural gas hydrate widely exists in continental permafrost and deep seabed, and has the characteristics of wide distribution, shallow burial, large scale, and high energy density. It is regarded as a potential unconventional energy source, and its proven reserves are equivalent to the global Twice the total amount of proven fossil fuels (coal, oil, natural gas). The traditional natural gas hydrate production methods mainly include depressurization method, thermal shock method and inhibitor injection method, but all of them have defects: low production efficiency of depressurization method, large energy dissipation of heat shock method, and damage to the environment by injection of inhibitor metho...

AI Technical Summary

Problems solved by technology

The traditional natural gas hydrate production methods mainly include depressurization method, heat shock method and inhibitor injection method, but all of them have defects: the depressurization method has low extraction efficiency, the heat shock method has large energy dissipation, and the inhibitor injection method damages the environment.

[0003] As the most promising natural gas hydrate extraction method, carbon dioxide replacement still has many problems in practical engineering: First, methane hydrate consists of 6 large cavities and 2 small cavities. The volume of carbon dioxide molecules is larger than that of methane, and its size is between methane Between the large and small cavities of the hydrate, under ideal conditions, the maximum recovery rate of methane can only reach 75%. Secondly, in the early stage of mining, carbon dioxide is rapidly replaced on the surface of methane hydrate, and gradually forms on the surface of hydrate as the replacement reaction progresses. The dense mixed hydrate layer of methane and carbon dioxide leads to a decrease in permeability, which is not conducive to the diffusion of carbon dioxide into the hydrate, and the replacement rate decreases rapidly. In severe cases, the replacement reaction basically stops

Therefore, in view of the problems of low methane recovery rate, carbon dioxide sequestration rate and low replacement rate, a new natural gas hydrate replacement method is urgently needed

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