Composite drill bit for submarine natural gas hydrate layer

Abstract

The invention discloses a composite drill bit for a submarine natural gas hydrate layer. The composite drill bit is mainly divided into three layers, wherein the first layer is a lead hole drill bit body for drilling a lead hole and is provided with a drilling fluid jet hole for cleaning the bottom of a well and assisting debris removal; the second layer is a hole expanding drill bit body for further expanding a wellbore and is provided with a spiral groove for facilitating discharge of rock debris; the third layer is a secondary crushing mechanism for refining large-diameter particles of hydrate sediments; meanwhile, a tapered flow passage for increasing a flow rate of the drilling fluid and a diffuser cavity for exciting the jet pressure are arranged in the drill bit body. The compositedrill bit provided by the invention is suitable for a fluidized mining process of submarine shallow natural gas hydrates, and is more in line with physical characteristics of a hydrate layer, therebyeffectively improving the crushing efficiency of a hydrate rock formation, realizing refinement of the large-diameter particles of the hydrate sediments, and solving problems of rock debris deposition, balling formation and drill tool sticking during long-distance horizontal drilling.

Description

technical field [0001] The invention relates to the technical field of natural gas hydrate exploitation, in particular to a composite drill bit for a subsea natural gas hydrate layer. Background technique [0002] Natural gas hydrate, also known as "combustible ice", is a "cage compound" formed by methane-based hydrocarbon gas and water under certain temperature and pressure conditions. It is a white solid substance with a density close to and slightly lower than that of Due to the density of ice, the discovered natural gas hydrates mainly exist in the permafrost areas in the Arctic region and in the seabed, continental slope, land base and trenches around the world. The types of storage layers mainly include sandstone, sandstone fracture, Fine-grained fracture type and dispersed type, and it usually exists in the seabed at a water depth of 300~3000m. Natural gas hydrates exist widely in the world. According to the evaluation results of relevant scientists, the distribution...

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Problems solved by technology

In addition, using the existing drill bit to break the hydrate rock formation will produce large-diameter hydrate sediment cemented particles, which are not easy to be sucked into the hydrate recovery channel, reduce the discharge speed of the hydrate mud slurry, and even form mud bags, resulting in serious problems such as drill sticking. as a result of

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