Method for constructing high-strength cavity at bottom of vertical well

Abstract

A method for constructing a high-strength cavity at the bottom of a vertical well is used for exploiting natural gas hydrates in sea areas, and comprises the following construction steps that drillinghydrate overlying strata; drilling a stratum below a hydrate bottom plate; expanding a cavity at the stratum under the hydrate bottom plate; pouring high-pressure cement paste without lifting a drillto form a high-strength cement primary pile; drilling the high-strength cement primary pile; secondary cavity expanding; removing slag in the cavity; cavity expanding detection; cementing and filling; and completing the vertical well bottom cavity construction. A reaming cast-in-place pile technology is adopted, by means of two-time cavity expanding and two-time pouring pile forming, the diameterof the primary pile is large, the final pile is subjected to cavity expanding pouring on the basis of the primary pile, the final pile is high in strength and regular in shape, the vertical well bottom cavity is built on the final pile, the stratum strength around the cavity is high, and the requirement on gathering gas production from multiple well groups of horizontal wells to the vertical wellcan be met.

Description

technical field [0001] The invention relates to the technical field of marine natural gas hydrate, in particular to a method for constructing a high-strength chamber at the bottom of a vertical well for natural gas hydrate in the sea. Background technique [0002] Although the test production of natural gas hydrate in the Shenhu area of ​​the South China Sea in 2016 has achieved great success, due to the limitation of the controllable reservoir area of ​​vertical wells, the daily gas production and the continuous stable production time are far from enough, and there is still a long way to go before the industrialization of hydrate production. For long distances, it is an inevitable trend to apply horizontal well drilling technology and multi-well group connection and convergence production technology to the pilot test area for gas hydrate test production. The current global sea area natural gas hydrate test production plan adopts the test production technology of the vertica...

AI Technical Summary

Problems solved by technology

For drilling in sea areas, due to the softness of the seabed, if you want to obtain a cavity with standard shape, high strength and stability, you must build a pile body whose strength gradually decreases from the center to the periphery. Stability plays a vital role. If the form of reaming cast-in-situ piles is directly used, the strength in the reaming cavity will be high, and the sudden transition to the soft seabed stratum is not conducive to the stability of the chamber; irregular in shape

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