Device and method for determining gas diffusion coefficient in rocks

A device for determining gas diffusion coefficient in rocks, comprising:

• a core holder for holding a rock sample in a middle;
• two sampling mechanisms respectively arranged at two ends of the rock sample, comprising:
• a first blind tube having an open end facing the rock sample and in sealing connection with an end surface of the rock sample to form a diffusion chamber;
• at least two closed sampling cavities;
• a cylinder having one end sequentially passing through the sampling cavities and extending into the diffusion chamber, wherein a cylinder wall of the cylinder is provided with a communication hole corresponding to each of the sampling cavities;
• a second blind tube coaxially sleeved in the cylinder and spaced a certain distance from the cylinder, wherein the second blind tube has a closed end facing the diffusion chamber and an open end in rotary sealing connection with the cylinder, so that an annular cavity communicated with the diffusion chamber is formed between the cylinder and the second blind tube;
• an outer wall of the second blind tube is provided with an open-loop sealing strip corresponding to the communication hole and a sampling hole passing through a tube wall and the sealing strip;
• when the second blind tube rotates relative to the cylinder, the communication hole is sequentially switched in the order of diffusion state, sampling state and isolation state, wherein the diffusion state refers to a state where the communication hole faces an opening of the sealing strip, the sampling state refers to a state where the communication hole is communicated with the sampling hole, and the isolation state refers to a state where the communication hole faces an outer wall of the sealing strip and is closed;
• the sampling holes are staggered along a circumference, so that the communication holes are sequentially communicated with the corresponding sampling holes when the second blind tube is rotated for sampling;
• a gas analyzer communicated with the open end of the second blind tube;
• a gas source communicated with the diffusion chamber;
• and
• a pressure gauge used to determine a pressure in the diffusion chamber.