Silty mudstone natural gas hydrate ground-layer compound type drilling fluid

Abstract

The invention discloses silty mudstone natural gas hydrate ground-layer compound type drilling fluid, and relates to the field of natural gas hydrate exploitation. The drilling fluid is prepared fromthe following components: polyethylene glycol, sodium chloride, potassium chloride, potassium humate, potassium polyacrylate, xanthan gum, polyvinyl caprolactam, propylene glycol monomethyl ether, tetrahexyltrimethyl ammonium bromide and prepared water. The silty mudstone natural gas hydrate ground-layer compound type drilling fluid can be used for silty mudstone natural gas hydrate storing and drilling, has the effects of resisting a low temperature, inhibiting and reducing the solid phase; a kinetic inhibitor and a synergist are added into the drilling fluid for compounding, so that relatively strong hydrate generation inhibition effect is achieved; and moreover, the drilling fluid is small in environmental harm by components, and has the advantages of being efficient, environmentally friendly, adopting cheap and easily available raw materials, and the like.

Description

technical field [0001] The invention relates to a compound drilling fluid for silty mudstone 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. 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 silty mudstone is mainly composed of clay minerals, containing a small amount of silty; the silt content is 25%-50%, and the clay content is 75%-50%; the silty mudstone reserves With unique structural features, it is mainly divided into massive structur...

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 natural gas hydrate storage in silty mudstone, due to the high clay content in silty mudstone, 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 natural gas in the drilling fluid Hydrates, clogging ducts and blowout preventers, causing serious safety incidents

However, the drilling fluid does not consider the low temperature of gas hydrate storage and the problem of hydrate inhibition.

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