Method of exploiting shallow massive type-I hydrate system based on warm sea water/gravel huff-puff exchange

Abstract

The invention discloses a method of exploiting shallow massive type-I hydrate system based on warm sea water / gravel huff-puff exchange. The method herein includes: (1) for a shallow type-I hydrate system reservoir with massive hydrates, drilling a main borehole that runs through a hydrate layer and a free gas layer, and perforating the free gas layer to reduce exploiting underlying gas; (2) drilling a main wheel and branch holes in the hydrate reservoir to increase the decomposition surface area for the massive hydrates, and performing the combination exploiting technique of surface sew waterhuff-puff process and fluid extraction depressurizing process so that the massive hydrates decompose gradually; (3) charging gravel sands of certain particle size to a formation in intermittent mannerto continuously fill formation deficient spaces caused by the decomposition of the massive hydrates so as to maintain formation stability and improve near-well-bore permeability, thereby promoting effective decomposition of the hydrates; executing the cycle so as to safely and continuously exploit the shallow massive hydrates. Continuous large-scale exploiting of natural gas hydrates is achieved,stable seabed environment and ecological system are maintained, and the green development concept is embodied.

Description

technical field [0001] The invention relates to the field of natural gas hydrate development in sea areas, in particular to a depressurization mining method for marine Type I hydrate systems based on warm seawater huff and puff-gravel replacement. Background technique [0002] Natural gas hydrate reserves are huge, and it is recognized as a potential energy source in the future. More than 90% of natural gas hydrate resources are stored in the ocean, which has aroused strong research interest and enthusiasm for development in many countries. How to exploit gas hydrate safely and effectively has become a hot issue in the field of gas hydrate. [0003] According to the symbiotic relationship between the hydrate sublayer and the underlying free air sublayer or water-bearing sublayer, marine hydrate reservoirs can be divided into type I hydrate system, type II hydrate system and type III hydrate system, among which type I hydrate The system means that the upper sublayer is a hyd...

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Problems solved by technology

[0005] 1. To decompose large-area massive hydrate ore bodies in the shallow layer, a large amount of heat needs to be added, so the simple depressurization method is not suitable for continuous mining of massive hydrate;

[0006] 2. Since shallow massive hydrates are part of the skeleton of seabed sediments, the thickness of some ore bodies can reach tens of meters. These hydrates will be produced during the process of decomposing from solid phase to gas-water two-phase. Leading to a large-area deficit in the strata, which can lead to rapid subsidence of the strata and cause environmental and ecological disasters;

[0007] 3. If there is free natural gas on the seabed below the massive hydrate reservoir, when the hydrate reservoir decomposes, it means that the caprock is destroyed, and the underlying natural gas will escape into the ocean and atmosphere, causing local geological disasters. Causing irreversible disasters to the marine ecological environment

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