Marine natural gas hydrate phase change refrigeration rope coring drilling tool and coring method

Abstract

The invention discloses a marine natural gas hydrate phase change refrigeration rope coring drilling tool and a coring method. The invention adopts phase change fluid as a refrigerant to exhaust gas generated by gasification of the phase change fluid from the interior of the drilling tool through a rapid gas exhaust mechanism, and solves the problem that the refrigeration capacity of the drillingtool is insufficient caused by the fact that the pressure in the cavity is too high, the critical point of the phase change pressure of the fluid is reached, and the fluid is not subjected to phase change heat absorption because the gas generated by phase change of the refrigerant cannot be exhausted under the action of deep sea hydrostatic pressure. The coring method includes the following steps:after coring is completed, putting a steel ball into the drilling tool to block a drilling fluid circulation channel; providing power to the rapid gas exhaust mechanism through the drilling fluid pressure; and injecting the refrigerant into a hole bottom freezing mechanism. The rope coring is combined with the freezing of the hole bottom to realize rapid coring without drilling; during drilling,the inner pipe assembly does not rotate, so that the damage to the natural gas hydrate core caused by the mechanical force generated by the rotation of the drilling tool is avoided to a greater extent, and the core recovery rate, integrity and representativeness are more effectively improved.

Description

technical field [0001] The invention relates to a marine natural gas hydrate phase-change refrigeration rope core drilling tool and a coring method, which is especially suitable for drilling and coring of deep-sea natural gas hydrate-containing sediments. Background technique [0002] As a potential energy source, natural gas hydrate has the characteristics of wide distribution, large amount of resources, shallow burial, high energy density, and cleanliness. energy. In order to truly understand gas hydrate, it is necessary to obtain high-fidelity gas hydrate samples. Drilling and coring is the most direct method to obtain gas hydrate samples, and it is also a necessary means to verify the investigation results of other methods. Due to the instability of natural gas hydrate occurrence, it can only exist under the condition of temperature lower than 0℃~10℃ and pressure higher than 10MPa. Once the temperature rises or the pressure decreases, methane gas will escape and solid ...

AI Technical Summary

Problems solved by technology

However, it is difficult to quickly freeze the gas hydrate core to the required low temperature due to conventional refrigerants

Therefore, it is proposed to use phase change fluids: liquid nitrogen, alcohol-dry ice mixture, liquid ammonia, acetone-dry ice mixture, etc., and use phase change fluids with large latent heat of vaporization as refrigerants to achieve rapid freezing of natural gas hydrate cores through phase change heat absorption However, in practical applications, due to the high hydrostatic pressure at the bottom of the hole, for example, the gas hydrate reservoir in the South my country Sea is located below 1,400 meters below the sea surface, and the hydrostatic pressure is greater than 14Mpa. Under the action of hydrostatic pressure, the gas produced by the phase transition of the refrigerant It cannot be discharged through a simple exhaust mechanism, causing the pressure in the drilling tool to rise above the phase equilibrium critical point of the refrigerant. At this time, the refrigerant stops vaporizing and absorbing heat, resulting in insufficient freezing energy to freeze the natural gas hydrate core to the required temperature, causing frozen gas hydrate cores to fail

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