An empirical method to compensate the NMR calibrated porosity of the tight volcanic rocks based on comprehensive laboratory studies

Abstract

The nuclear magnetic resonance (NMR) response is known to deviate from the true value for the volcanic reservoirs, particularly when the pore throat size is ultralow. Consequently, the related petrophysical parameters such as porosity, permeability, and pore size distribution from NMR measurements are greatly influenced. An empirical method to correct the NMR calibrated porosity for the tight volcanic rocks is proposed after comprehensive investigations of influential factors combined with mineralogical and petrophysical analyses. The laboratory result indicates that the relative porosity deviation is negatively correlated with the geometric mean of the transversal relaxation time (T2) but positively correlated with the clay content. Moreover, both the paramagnetic materials, such as the manganese (Mn) content, and the diamagnetic materials, such as the magnesium (Mg) content, contribute to the NMR relaxation intensity reduction but with different mechanisms. The NMR calibrated porosity can be compensated through multiple regressions with these controlling factors, which can be generalized to other tight volcanic reservoirs.

Different Fracture Liquids under the Action of Enclosure of Dense Sandstone Reservoir Micro-Damage Characteristics Study

“…Zhu Huayin et al conducted gas-driven water experiments for various types of sandstone samples, and in-depth research on the form of water in the rock pores combined with nuclear magnetic resonance technology. GUO et al [21]. adopted MRI's resonance imaging technology and T2 spectrum analysis methods to deeply discuss the pore classification of sandstone and the uniformity of the pore diameter distribution during the driving process.…”