Compound drilling fluid applied to stratums with natural gas hydrates in seafloor

Abstract

The invention provides compound drilling fluid applied to stratums with natural gas hydrates in the seafloor and relates to the field of exploitation of natural gas hydrates. The drilling fluid comprises the following components: polyethylene glycol, sodium chloride, ethylene glycol, low-viscosity carboxymethyl cellulose LV-CMC, potassium polyacrylate, xanthan gum, polyvinyl caprolactam, propyleneglycol phenyl ether, tetranbutylammonium phosphate and prepared water. The compound drilling fluid is capable of being applied to drilling with storage of the natural gas hydrates in the seafloor, isfree of solid phase and has resistance to low temperature; kinetic inhibitors and synergists are added into the drilling fluid and are compounded with each other; the drilling fluid has a relativelystrong effect of inhibiting generation of the hydrates; meanwhile, the components of the drilling fluid are low in harm to environment; and the drilling fluid has the advantages of high efficiency, environment friendliness and cheap and easily available raw materials.

Description

technical field [0001] The invention relates to a compound drilling fluid for subsea natural gas hydrate formation, in particular to the field of natural gas hydrate exploitation. Background technique [0002] Natural gas hydrates are mainly distributed in the deep-water areas of the continental margins and the permafrost areas on land, and the former accounts for the vast majority of the discovered quantities. Natural gas hydrate is one of the potential alternative energy sources, and the research on natural gas hydrate is a hot spot in contemporary earth science and energy industry development research. There are a large amount of natural gas hydrates in seabed sediments. Drilling is an essential means to explore and develop natural gas hydrates at a certain depth underground. The phase equilibrium property of gas hydrate determines that drilling in this type of formation is very different from drilling in general oil and gas formations, and it also leads to more complex ...

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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