Drilling fluid for natural gas hydrate reservoir in argillaceous siltstone

Abstract

The invention relates to drilling fluid for natural gas hydrate reservoir in argillaceous siltstone, which relates to the field of natural gas hydrate exploitation. The drilling fluid disclosed by theinvention consists of the following components: sodium silicate, sodium chloride, glycol, potassium chloride, low-viscosity carboxymethylcellulose LV-CMC, potassium polyacrylate, xanthan gum, polyvinylpyrrolidone K90, propylene glycol monomethyl ether, ethylene glycol mono-n-butyl ether and prepared water. The drilling fluid, which can be used in the drilling of natural gas hydrate reservoir in argillaceous siltstone, has low temperature-resistant, inhibiting and solid phase-reducing effects; by adding a kinetic inhibitor to be compounded with a synergist, the drilling fluid has a high hydrate formation inhibition effect, moreover, the environmental hazard of the components of the drilling fluid is low, and the drilling fluid has the advantages of high effectiveness, environment friendliness, cheap and easy-to-obtain raw materials and the like.

Description

technical field [0001] The invention relates to a drilling fluid used for argillaceous siltstone natural gas hydrate storage, 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. The proportion of sand and mud in natural gas hydrate storage has a great influence on the properties of the formation itself and the saturation of hydrate in it. The storage is divided into silty mudstone, argillaceous siltstone, siltstone, sandstone and glutenite. Its hydrate content can reach up to 95%; the argillaceous siltstone structure is granular and has good water permeability. The main component is silt, containing a small amount of clay minerals and cement. It is 70%-50%; the argillaceous siltstone reservoir has unique structural characteristics,...

AI Technical Summary

Problems solved by technology

[0004] (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

[0005] (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, which further reduces the stability of the well wall, 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

[0007] (4) For argillaceous siltstone natural gas hydrate storage, due to the composition of argillaceous siltstone and high clay content, a large amount of clay enters the drilling fluid during drilling, which increases the viscosity of the drilling fluid and makes it easier to form in the drilling fluid. Gas hydrates, clogging conduits and blowout preventers, causing serious safety incidents

However, none of the above drilling fluids addresses the problem of excessive clay content during drilling in muddy siltstone reservoirs.

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