Method and device for testing wettability of dense oil reservoir

A method for testing wettability of a tight oil reservoir, the method comprising:

• testing nuclear magnetic resonance T2 maps of the tight oil reservoir in a saturated water state and in a saturated oil state;
• calculating a water-wetting coefficient and an oil-wetting coefficient of the tight oil reservoir according to the nuclear magnetic resonance T2 maps of the tight oil reservoir in the saturated water state and in the saturated oil state;
• calculating a mixed wettability index of the tight oil reservoir by using the water-wetting coefficient and the oil-wetting coefficient of the tight oil reservoir, and determining the wettability of the tight oil reservoir according to the mixed wettability index;
• wherein calculating a mixed wettability index of the tight oil reservoir includes:
• calculating a difference between the water-wetting coefficient and the oil-wetting coefficient to obtain the mixed wettability index of the tight oil reservoir,
• wherein calculating a water-wetting coefficient and an oil-wetting coefficient of the tight oil reservoir includes:
• placing the nuclear magnetic resonance T2 maps of the tight oil reservoir in the saturated water state and in the saturated oil state, into the same coordinate system;
• by using a T2 cutoff value, dividing the nuclear magnetic resonance T2 maps in the same coordinate system into left and right sections, wherein the left half section is a nuclear magnetic resonance T2 map of a boundary fluid part;
• calculating an amount of bound water and an amount of bound oil in the boundary fluid according to the nuclear magnetic resonance T2 map of the boundary fluid part;
• and
• calculating the water-wetting coefficient and the oil-wetting coefficient according to the amount of the bound water and the amount of the bound oil;
• wherein testing nuclear magnetic resonance T2 maps in a saturated water state and in a saturated oil state includes:
• taking out a first pillar from the tight oil reservoir;
• causing the first pillar to reach the saturated water state, and testing the nuclear magnetic resonance T2 map of the tight oil reservoir in the saturated water state;
• and
• after removing a nuclear magnetic signal of water in the first pillar, causing the first pillar to reach the saturated oil state, and testing the nuclear magnetic resonance T2 map of the tight oil reservoir in the saturated oil state.