Natural gas hydrate parallel horizontal well miscible-phase displacement mining method

Abstract

The invention discloses a natural gas hydrate parallel horizontal well miscible-phase displacement mining method and belongs to the technical field of natural gas hydrate mining. The method includes the steps that in combination with geological data, a parallel horizontal well network is arranged for a target reservoir; matched well-completion operation is performed; after well completion is finished, depressurizing mining is performed through horizontal wells till no economic benefit exists; after depressurizing mining is finished, fracturing operation is performed on the horizontal wells; then a ground supply system and an underground injection system are arranged at the injection wells; and carbon dioxide and chemical agents are separately injected into the natural gas hydrate reservoirthrough the injection wells, and natural gas and produced water are collected from the producing wells. The natural gas hydrate parallel horizontal well miscible-phase displacement mining method is suitable for the reservoir which is low in permeability, poor in communication property, rich in storage and low in natural gas hydrate saturability; the horizontal wells distributed in parallel are arranged for the target reservoir so that the storage amount of the available natural gas hydrate can be increased; and mining is performed by separately injecting the carbon dioxide and the chemical agents through the injection wells, the gas mining efficiency can be improved, the ultimate recovery factor is improved, and the economic benefits are improved.

Description

technical field [0001] The invention relates to a method for producing natural gas hydrate by miscible flooding in parallel horizontal wells, which belongs to the technical field of natural gas hydrate production. Background technique [0002] Natural gas hydrate (NGH for short) is a non-stoichiometric clathrate compound formed by natural gas and water at a certain low temperature and high pressure, also known as "combustible ice". 1m 3 Natural gas hydrate can contain 164m 3 methane gas and 0.8m 3 of water. "Combustible ice" is a secondary product of natural gas, and its application range is roughly the same as that of natural gas. It is a typical oil substitute. "Combustible ice" is extremely flammable. Under the same conditions, the energy generated by the combustion of "combustible ice" is dozens of times higher than that of coal, oil, and natural gas. It is known as "the super energy of the future". [0003] my country is rich in combustible ice reserves. According ...

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Problems solved by technology

However, the decomposition driving force provided by the depressurization method alone is small, and the decomposition of natural gas hydrate causes the temperature to drop. When the temperature drops below 0°C, it will also cause ice blockage and stagnation of natural gas hydrate decomposition. CN 20111048906.4 discloses a drainage The natural gas hydrate is exploited by depressurization and heating at the same time, which continuously promotes the decomposition of hydrate. The above two methods use the gas escaping after the hydrate is decomposed, and the water falls due to its own weight. The water pump discharges the water out of the natural gas hydrate production well. But in fact, the decomposed gas carries a large amount of water vapor when it escapes, and the escape speed is very slow, and the extraction efficiency is very low

Moreover, in CN 20111048906.4, horizontal wells are used for combustion and heating. It is unsafe to burn and heat in natural gas hydrate exploitation wells. There are combustible gases inside and outside the natural gas hydrate exploitation wells. It is very dangerous to use open flames for direct heating.

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