Low-permeability sandstone reservoir pore structure quantitative inversion method based on nuclear magnetic resonance

Abstract

The invention discloses a low-permeability sandstone reservoir pore structure quantitative inversion method based on nuclear magnetic resonance. The method comprises the following steps: I, selecting a basic sample; II, classifying the type of a pore structure; III, establishing a well logging chart for identifying the pore structure; IV, establishing a pore throat distribution inversion formula according to the type of the pore structure; V, verifying the accuracy of the formula; VI, identifying the type of the pore structure of a shaft section by utilizing the well logging chart; VII, quantitatively inverting the distribution of free fluid pore throats by utilizing a nuclear magnetic resonance well logging T2 spectrum. The method has the following beneficial effects: a reliable method and technology are provided for quantitatively evaluating the pore structure, and the research concept of the current method can be broken through. The continuous free fluid pore throat distribution can be inverted by virtue of the nuclear magnetic resonance well logging, so that direct evidence is provided for evaluating the effectiveness of the low-permeability sandstone reservoir, application of the well logging information in the quantitative inversion of the micro pore structure of the reservoir is favorably explored, and the application and development of the nuclear magnetic well logging technology can be promoted.

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...

AI Technical Summary

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

Images