TECHNICAL FIELD

The present invention relates to a device and method for measuring a horizontal/vertical permeability of a hydrate reservoir.

BACKGROUND

Natural gas hydrates (NGH) are widespread in nature, and methane hydrates are currently a potential strategic resource. Carbon dioxide is used to achieve the effective replacement of methane in hydrates in actual reservoirs. This method mines methane and makes full use of carbon dioxide in the atmosphere, which effectively reduces the greenhouse effect caused by carbon dioxide. Therefore, it is considered to be the most economical and environmentally friendly way to mine methane hydrates. During the injection of carbon dioxide, the horizontal/vertical permeability of the hydrate reservoir determines the gas flow performance in the reservoir, which has an important impact on the distribution of carbon dioxide in the reservoir. At present, there are many experimental devices for measuring the permeability of hydrate reservoirs, but none of them can measure the horizontal/vertical permeability. Therefore, it is impossible to further comprehensively understand the influence of hydrates on the permeability of the reservoir. In view of this, an experimental device for measuring the horizontal/vertical permeability of hydrate reservoirs is designed according to the needs of actual research.

SUMMARY

In order to overcome the shortcomings in the prior art, the present invention proposes a device and method for measuring a horizontal/vertical permeability of a hydrate reservoir.

A device for measuring a horizontal/vertical permeability of a hydrate reservoir includes a cooling water/saturated methane water tank, a water injection pump, a methane gas tank, a booster pump, an air compressor, a high-pressure gas tank, a back pressure valve, a gas tank, a data acquisition instrument, a constant-temperature water bath and a hydrate reservoir horizontal/vertical permeability measuring apparatus provided in the constant-temperature water bath, where

the cooling water/saturated methane water tank is provided with a water circulation inlet and an intake line at an upper part and a water circulation outlet at the bottom; the intake line is provided thereon with an intake control gate valve; the bottom of the cooling water/saturated methane water tank is in communication with the water injection pump;

the methane gas tank and the air compressor are both in communication with the booster pump, and the booster pump is in communication with the high-pressure gas tank;

the water injection pump and the high-pressure gas tank are both in communication with an inlet of the hydrate reservoir horizontal/vertical permeability measuring apparatus; an outlet of the hydrate reservoir horizontal/vertical permeability measuring apparatus, the back pressure valve and the gas tank communicate in sequence; the gas tank is provided thereon with an exhaust line; the exhaust line is provided thereon with a gas flow meter;

the hydrate reservoir horizontal/vertical permeability measuring apparatus is provided thereon with a P1 horizontal differential pressure gauge, a P2 horizontal differential pressure gauge, a P3 horizontal differential pressure gauge, a P4 vertical differential pressure gauge, a P5 vertical differential pressure gauge and a P6 vertical differential pressure gauge;

the data acquisition instrument is electrically connected to the P1 horizontal differential pressure gauge, the P2 horizontal differential pressure gauge, the P3 horizontal differential pressure gauge, the P4 vertical differential pressure gauge, the P5 vertical differential pressure gauge, the P6 vertical differential pressure gauge and the gas flow meter;

the inlet of the hydrate reservoir horizontal/vertical permeability measuring apparatus includes a left inlet and a bottom inlet; the outlet of the hydrate reservoir horizontal/vertical permeability measuring apparatus includes a top outlet and a right outlet.

Further, the hydrate reservoir horizontal/vertical permeability measuring apparatus includes a reaction vessel, an inlet cover, an outlet cover, an inlet left clamp, an inlet right clamp, an outlet left clamp and an outlet right clamp; the inlet cover is fixed to an upper end of the reaction vessel through the inlet left clamp and the inlet right clamp; the outlet cove is fixed to a lower end of the reaction vessel through the outlet left clamp and the outlet right clamp.

Further, the intake line is further provided thereon with a pressure gauge.

Further, the gas tank is provided with a balance scale on the bottom.

Further, the cooling water/saturated methane water tank is provided therein with a bubbler.

Further, the high-pressure gas tank is provided thereon with a gas tank pressure gauge; the inlet of the hydrate reservoir horizontal/vertical permeability measuring apparatus is provided with a reactor inlet pressure gauge.

A method for measuring a horizontal/vertical permeability of a hydrate reservoir includes the following steps:

(1) loading a dried quantitative porous medium used for simulation into a hydrate reservoir horizontal/vertical permeability measuring apparatus;

(2) starting an air compressor and a booster pump to inject a gas into a high-pressure gas tank to a required gas pressure;

(3) injecting the gas into the hydrate reservoir horizontal/vertical permeability measuring apparatus to a certain pressure to check the tightness of the equipment to ensure that the equipment does not leak;

(4) adjusting the temperature of a constant-temperature water bath to a required temperature; opening a water circulation inlet and a water circulation outlet; starting an intake line, so that a gas enters a cooling water/saturated methane water tank through a bubbler and the methane gas dissolves in the water sufficiently to produce methane water; adjusting the temperature to the same temperature as the constant-temperature water bath;

(5) starting a water injection pump to inject water at a certain temperature into the hydrate reservoir horizontal/vertical permeability measuring apparatus and a related process; discharging the air in the porous medium and a pipeline; adjusting a back pressure valve to 5 MPa until a liquid in a gas tank has a constant flow rate and a liquid volume thereof is kept in balance with a discharge volume of the water injection pump;

(6) discharging the air from a P1 horizontal differential pressure gauge, a P2 horizontal differential pressure gauge, a P3 horizontal differential pressure gauge, a P4 vertical differential pressure gauge, a P5 vertical differential pressure gauge and a P6 vertical differential pressure gauge to ensure that the pipeline is filled with water;

(7) adjusting a reaction vessel to a certain pressure, and monitoring the data in real time by a reactor inlet pressure gauge, so as to keep a constant state;

(8) discharging a portion of the gas from the high-pressure container to displace water in the hydrate reservoir horizontal/vertical permeability measuring apparatus and provide space for the gas, and adjusting the reaction vessel to a certain pressure;

(9) starting the water injection pump to inject water into the hydrate reservoir horizontal/vertical permeability measuring apparatus to a certain pressure, and stopping the water injection pump;

(10) allowing a hydrate to be synthesized in the hydrate reservoir horizontal/vertical permeability measuring apparatus, and completing the hydrate formation after a period of time;

(11) adjusting the back pressure valve to a required pressure; starting the water injection pump to inject water into the hydrate reservoir horizontal/vertical permeability measuring apparatus at a constant speed until the flow rate of the gas tank remains constant; checking a gas flow meter to ensure that the hydrate is not decomposed, and obtaining a change in different differential pressures of a hydrate sample in a horizontal direction;

(12) after the test is completed, starting the water injection pump to inject water into the hydrate reservoir horizontal/vertical permeability measuring apparatus at the same speed as the horizontal permeability measurement process until the flow rate of the gas tank remains constant; checking the gas flow meter to ensure that the hydrate is not decomposed, and obtaining a change in different differential pressures of the hydrate sample in a vertical direction;

(13) recording the relevant data of the entire hydrate formation process and the testing process with a data acquisition instrument; and

(14) processing the relevant data based on Darcy's Law to obtain a change in the horizontal/vertical permeability.

The present invention has the following beneficial effects:

(1) The device realizes the measurement of the horizontal/vertical permeability under the same saturation through the design of a core container.

(2) The device is designed with different pressure outlets from different directions to obtain the pressure difference of different test sections, which is helpful to obtain the permeability at different locations to comprehensively study the effect of a hydrate on a porous medium.

(3) A new cooling water device is added to improve the testing process to ensure that the hydrate in the reservoir is not decomposed, which greatly reduces the decomposition of the hydrate during the test.

(4) An inlet and an outlet are connected by a clamp and matched with a rubber sealing ring to achieve effective sealing of a fluid and facilitate disassembly.

