Method for multistage sand prevention of ocean natural gas hydrate depressurization production

Abstract

The invention discloses a method for multistage sand prevention of ocean natural gas hydrate depressurization production. The method comprises a step S1 of adopting low production pressure difference to perform depressurization production, first decomposing and exploiting hydrate of an earth layer outside a sleeve pipe and close to a well, discharging mud and silty sand ingredients of the earth layer, and only making uniform sand which is good in grain size and good in sorting coefficient remain; a step S2 of performing filling outside a pipe, squeezing the mud-removed coarse sand belt to the periphery of a gravel layer to achieve an effect of a primary sand-blocking barrier; making a filling belt outside the pipe serve as a secondary sand-blocking barrier; a step S3 of selecting gravel with the dimension larger than a filling pipe outside the pipe by one grade to perform filling in the pipe, and making the filling layer in the pipe achieve an effect of a third-stage sand-blocking barrier; making an internal sand-blocking screen cloth serve as a fourth-stage sand-blocking barrier; and a step S4 of performing step type step-by-step enlargement of production pressure differential to a set value. The sand prevention problem caused by high mud content of an ocean hydrate layer and large pressure drop range is solved fundamentally, the problem of difficulty in forming a downhole filling belt sand bridge is solved through step type enlargement of production pressure differential, and the hydrate well productivity is improved.

Description

technical field [0001] The invention relates to the technical field of exploitation of natural gas hydrate resources in sea areas, in particular to a multi-stage sand control method for depressurization exploitation of marine natural gas hydrate. Background technique [0002] Hydrate resources have the characteristics of large resources, high energy density, and shallow buried depth of reservoirs. Therefore, Europe, America, Japan, India, South Korea and China have conducted a lot of basic research and formed a series of hydrate resource mining methods. The currently formed natural gas hydrate development methods mainly include thermal shock mining, decompression mining, chemical reagent injection mining, displacement mining and solid mining. Judging from the existing trial production experience, these hydrate mining methods face a common problem: sand production severely restricts the effective development of hydrate. The Mallik 5L-38 project in Canada (2002) successfully...

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Problems solved by technology

[0005] (2) High shale content in sea hydrate reservoirs

In this case, the clogging of mud on the sand control medium will further increase, and the production capacity will be severely reduced

If the production pressure difference is increased blindly under the single requirement of hydrate decomposition speed, it will lead to the rupture of the sand control medium and the failure of sand control;

[0007] (4) Hydrate reservoirs in sea areas usually have shallow burial depth, large formation sand heterogeneity coefficient, and poor sorting, so it is difficult to design the filling layer, and it is difficult to design a single gravel size to simultaneously block fine sand components and medium-coarse sand groups. Therefore, the traditional sand control process design method is difficult to meet the design requirements of hydrate reservoirs, and the sand control effect is poor.

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