Method and device for measuring coal wettability under high pressure through low-field nuclear magnetic resonance

Abstract

The invention discloses a method and device for measuring coal wettability under high pressure through low-field nuclear magnetic resonance. The method comprises the following steps: performing low-field nuclear magnetic resonance measurement on water in pulverized coal under a standard condition to obtain a T2 spectrum of the water in the coal, and according to the position and the amplitude of afirst peak on the right side of the T2 spectrum, acquiring the geometric mean value T2g of the relaxation time T2 of the spectral peak; in combination with a measurement result theta of the water contact wetting angle of the conventional moulded coal surface in a parallel experiment, establishing a relational expression of a water wetting angle by using normalized T2g and NT2g: theta=84.376*NT2g+52.612; according to the relational expression, in combination with the T2g value of the water in the coal under a high-pressure condition, working out the water wetting angle of the coal under a setgas pressure. The device comprises a gas source, a sealed constant-pressure system and a nuclear magnetic magnet, wherein the nuclear magnetic magnet is connected with a low-field nuclear magnetic resonance instrument. According to the method, through establishment of a scaling relation between the coal wettability and a nuclear magnetic resonance T2 spectrum signal, quantitative determination ofthe coal wettability under different gas pressures is achieved; the method is new method for measuring the coal wettability instantly, in situ and dynamically.

Description

technical field [0001] The invention belongs to the technical fields of measurement of reservoir physical property evaluation and coal washing and processing in the process of coalbed methane exploration and development, and in particular relates to a method and device for measuring wettability of coal under high pressure by using low-field nuclear magnetic resonance. The invention is mainly used for measuring the wettability of coal under high pressure, but is also applicable to the measurement field of physical property evaluation of oil and gas reservoirs, such as the wettability measurement of sandstone, carbonate rock and other reservoir samples. Background technique [0002] Wettability refers to the ability or propensity of a liquid to spread on a solid surface. This tendency is very important for the development of coalbed methane, which involves the two-phase seepage process of gas and water in the formation during the development process. Wettability is one of the...

AI Technical Summary

Problems solved by technology

At present, the methods applicable to the quantitative determination of the wettability of conventional rock samples mainly include: (1) the centrifuge (USBM, United States Bureau of Mines) method and the Amott method, both of which are based on displacement experiments. Most of the samples are low porosity and low permeability, so the effect of displacement experiment is not good

(2) Contact angle method. Although the measurement results of this method are intuitive and accurate, when this method is applied to coal rocks, the results are affected by the heterogeneity of coal rock composition, and the error is large

On the contrary, for weakly water-wet samples, the wetting contact angle is larger, and the wetting tension of the water between the coal powder particles is small, which leads to the slowing down of the migration of water droplets between the particles, and the T of the P3 peak 2 No significant change in relaxation time

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