Abstract: The variation of porosity in elastic deformation of rock is studied in two aspects. Firsly, based on the four compressibility factors in rock and their relations among them, it is proved theoretically that the porosity variation is related closely with the net confining pressure, showing that if the net confining pressure is invariable, so is the porosity; otherwise, the porosity is variable. Secondly, the experimental data are used to testify that the porosity is variable in elastic deformation. Such a disproof method means that the formula for rock matrix compressibility factor at constant porosity is deduced followed by substituting the experimental data into the fomula, comparing calculated value with measured value of the compressibility factors. If the difference of both values is extremely large, the former hypothesis is not valid, namely the porosity is variable. The results from the theoretical and experimental analyses indicate that the porosity is nomally variable during elastic deformation of rock, hence porosity correction has the basis, whereas the principle of porosity invariability is not valid.

Key words: rock, elastic defommation, porosity, compressibility factor, disproof method