Drilling fluid for marine natural gas hydrate (NGH) reservoir

Abstract

The invention discloses a drilling fluid for marine natural gas hydrate (NGH) reservoir, and relates to the field of NGH exploitation. The drilling fluid comprises following components: sodium silicate, sodium chloride, glycol, potassium humate, potassium polyacrylate, xanthan gum, polyvinylpyrrolidone K90, propylene glycol monomethyl ether, mono-n-butyl glycol ether, and make-up water. The drilling fluid is suitable for NGH drill wells in the sea, does not contain any solid phase, and is resistant to low temperature. The drilling fluid is compounded with a kinetic inhibitor and a synergist toinhibit the generation of hydrates. Moreover, the components of the drilling fluid are basically harmless to the environment, and the drilling fluid has the advantages that the efficiency is high, the environment is protected, and the raw materials are cheap and easily available.

Description

Technical field [0001] The invention relates to a drilling fluid for marine natural gas hydrate storage, in particular to the field of natural gas hydrate exploitation. Background technique [0002] Natural gas hydrates are mainly distributed in deep ocean waters on continental margins and permafrost on land. The former accounts for the vast majority of the discovered quantities. Natural gas hydrate is one of the potential alternative energy sources. The research on natural gas hydrate is a hot spot in contemporary earth science and energy industry development research. The seabed sediments contain a large amount of natural gas hydrates. To explore and develop the natural gas hydrates stored in a certain depth underground, drilling is an indispensable important means. The phase balance nature of natural gas hydrate determines that this type of formation drilling is very different from general oil and gas formation drilling, and it also causes this type of formation drilling to f...

AI Technical Summary

Problems solved by technology

[0003] (1) When drilling in natural gas hydrate formations, due to the release of formation stress near the well wall and bottom of the reservoir, the formation pressure will decrease; and the drill bit will cut rock, and the friction between the bottom drilling tool and the well wall and core will generate a large amount of Thermal energy destroys the temperature and pressure conditions for the stable existence of hydrates; thus triggering the decomposition of hydrates, resulting in instability of the well wall and adverse effects on drilling operations

[0004] (2) The invasion of drilling fluid and the decomposition of hydrates will lead to the increase of formation pore pressure in different degrees, and the increase of pore pressure will increase the density of drilling fluid required to maintain the stability of the wellbore wall, which not only seriously affects the penetration rate, but also increases the pressure of the wellbore wall. Seepage increases the pore pressure around the well, thereby further reducing the stability of the well wall and forming a vicious circle

Moreover, the decomposition of hydrates will also increase the permeability of the formation, and the drilling fluid will seep into the well wall to generate osmotic pressure, which will increase the collapse pressure of the formation and reduce the fracture pressure, making the well wall more likely to collapse and fracture, reducing the stability of the well wall

[0006] (4) For subsea natural gas hydrate storage, during the drilling process of natural gas hydrate storage, the decomposition of gas hydrate will rapidly increase the ultra-static pore pressure in the storage soil, which may cause submarine landslides or instability of the subsea foundation, which may lead to Cause damage to drilling holes, drilling platforms, submarine pipelines and other facilities

The above drilling fluids all have certain effects on the drilling of natural gas hydrate reservoirs, but none of them consider the use of compound hydrate inhibitors

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