Quantitative inversion method of pore structure in low-permeability sandstone reservoir based on nuclear magnetic resonance

Abstract

The invention discloses a method for quantitative inversion of pore structure of low-permeability sandstone reservoirs based on nuclear magnetic resonance, comprising the following steps: first, selecting basic samples; second, classifying pore structure types; Well chart; fourth, establish pore throat distribution inversion formula by pore structure type; fifth, verify the correctness of the formula; sixth, use logging chart to identify the pore structure type of wellbore section; seventh, use nuclear magnetic resonance Quantitative inversion of free fluid pore throat distribution by well T2 spectrum. The beneficial effects of the invention are as follows: it provides a reliable method and technology for quantitatively evaluating the pore structure, and breaks the research idea of ​​the current method. Along the wellbore section, the continuous free-fluid pore-throat distribution obtained by NMR logging inversion provides a direct basis for the evaluation of the effectiveness of low-permeability sandstone reservoirs, and is also beneficial for the quantitative inversion of the microscopic pore structure of the reservoir by logging information. The exploration has promoted the application and development of nuclear magnetic logging technology.

Description

technical field [0001] The invention relates to the fields of core nuclear magnetic resonance, mercury injection experiment and nuclear magnetic resonance logging, in particular to a quantitative inversion method for the pore structure of low-permeability sandstone reservoirs based on nuclear magnetic resonance. Background technique [0002] NMR is based on the interaction of the magnetic properties of atomic nuclei and their applied magnetic fields. Under the action of an external magnetic field, the protons in the formation fluid are polarized, and the spatial orientation of nuclear spins changes from disorder to order. After polarization, turn off the external magnetic field, and measure the time (relaxation time) of the spin system from the unbalanced state to the balanced state, that is, measure the longitudinal relaxation time T 1 , the transverse relaxation time T 2 . [0003] The original data of magnetic resonance logging is the spin echo train that decays with t...

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Problems solved by technology

[0032] Method 1 is an improvement to Method 2. Different power functions are used to construct pseudo-capillary pressure curves, and the agreement with the capillary pressure curves obtained by mercury intrusion has improved to some extent compared with the previous ones. 2 It is obtained by integrating the spectrum, and its maximum saturation is 100%, which does not take into account the problem of maximum mercury saturation, which has certain limitations

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