Method and apparatus for realizing double-gradient well drilling

Abstract

The present invention relates to a method for implementing double-gradient well-drilling operation and its equipment. Said method includes the following steps: (1), the drilling fluid in which the light microspheres are mixed in sea surface is passed through top drive and drill pipe, and transferred to the well bottom by means of slurry pump; (2), the above-mentioned drilling fluid in which the light microspheres are mixed is passed through a separation injection device to separate out the microspheres from drilling fluid and make said microspheres be injected into the annular space between the drill pipe and well bore, the separated drilling fluid can be continuously flowed towards well bottom along the drill pipe; (3), the drilling fluid is passed through down hole safety valve and drill bit and reached to well bottom, then back-returned by means of annular space between well bore and drill pipe; (4), after the drilling fluid back-returned from the well bottom is diluted by microspheres positioned in annular space between well bore and drill pipe, two different pressure gradients are formed in the annular space between well bore and drill pipe; and (5), the drilling fluid containing light microspheres can be back0returned to sea surface from the annular space between well bore and drill pipe, and can be continuously reutilized.

Description

technical field

[0001] The invention relates to a method and device for offshore drilling, in particular to a method and device for realizing dual-gradient drilling. Background technique

[0002] In conventional deepwater drilling, the drilling ship and the subsea wellhead are connected by a riser, and the drilling fluid flows downward through the drill pipe, passes through the drill bit, and then flows upward through the annulus between the drill pipe and the wellbore, and the lowered casing section ( conduit section), the riser above the seabed, and circulate back to the drilling ship. There is only one pressure gradient of mud in the whole drilling circuit. When drilling in deep water exceeding 500m, the conventional drilling using the riser system will be prone to technical difficulties that are difficult to overcome with conventional drilling equipment and methods, including: 1. The mooring rig itself must bear the weight of the mooring system, which increases the stab...

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