I. Overview
Porosity is one of the important properties of rock. It is defined as the ratio of pore volume to the geometric volume of rock, usually expressed as a percentage. The size of the pore space occupied by hydrohydrocarbons in the oilfield is an essential parameter for both the reasonable evaluation of the reservoir and the engineering of the reservoir.
Based on the porosity meter of American core Company and referring to a large number of data, the gas porosity meter designed by US has the characteristics of simple structure, convenient operation, fast determination speed, stable performance and so on. It is an essential device for core analysis laboratory.
Two, the working principle
Gas porosity meter is an instrument for measuring volume, which can be used to measure the skeleton volume and porosity volume of rock samples. The gas expansion principle, namely BoyLE's law, is used to measure the final equilibrium pressure after the gas of a known volume isothermal expansion to an unknown volume under a certain pressure. The equilibrium pressure depends on the unknown volume, which is determined by Boyle's law.
The instrument can use two gases as displacement media, nitrogen and helium. Nitrogen can be used for general sandstone, and helium can be used for relatively dense limestone and rock samples with small pores.

The reason for using helium is:

①. Tiny helium (molecular radius r=0.9A) as a medium can enter the capillaries associated with reservoir rocks.

②. Helium gas with low molecular weight (M=4) has higher permeability to rocks.

③. The rock surface has poor helium absorption.
According to Boyle's law:

The known volume Vk of the gas expands isothermically with the measured pressure Pk into the unknown chamber volume V. After the expansion, the final equilibrium pressure P is measured. The equilibrium pressure depends on the unknown volume, which can be obtained by using Boyle's law.

Main technical index

1Measuring range:60%;

2Pressure gauge: digital display, measuring range0~10MPa, display accuracy:0.5% F.S;

3, core holderA: φ25x25~76mm;

4, core holderB: φ38x38~76mm;

5Measurement accuracy: ±0.5%;

6, overall size:400*400*400mm;

7Gas medium: dry nitrogen or helium;

8Control range of confining pressure:0~3MPa;

9, equipped3A gas cylinder and gas; (Note:10Platform porosity tester equipped)

10, equipped2A matching tank box, material: iron, surface spray paint; (Note:10Platform porosity tester equipped)

11, drying core drying oven1Liner size:350*350*350mm, overall size:450*650*550mm, gross weight:40KG, accuracy ±1℃, timing range:1-9999min; 12, equipped with a set of oil washing instrument: fat extractor type (Note: 10 sets of porosity measuring instrument equipped)