PRELIMINARY EXPERIMENTAL STUDY ABOUT EFFECT OF DEFORMATION ON ORGANIC MATURITY

Three kinds of coal samples were coaxially deformed with Griggs-type rock experiment apparatus under high temperature and confining pressure. The vitrinie reflectance of original samples is 4.90% (coal sample L), 3.41% (coal sample X) and 0.67% (coal sample J) respectively. Phyrophyllite was used as confining pressure medium. Strain rates were kept constant during each experiment. The temperature condition is 350～700℃ and the confining pressure range is 400～600MPa. The shape of samples is column with 19mm in diameter and 40mm in length. Samples were kept open to outside during experiment so that produced gas can be vented out continually. In this paper some questions about effects of structural deformation on organic maturity are discussed by analysis to the changes of vitrinite reflectance in the samples which are of different strain and stress but of same temperature and confining pressure and near deformation time. It is indicated that increase of vitrinite reflectance is of positive relationship to stain. This result is similar to that of Mastalerzs (1993) study (although there are some differences in sample and condition of apparatus between these two studies) and further proved that structural deformation can promote the level of organic maturity. Deformation, as compared with time and temperature, is a subsidiary factor to organic maturity. Deformation alone can not cause the increase of organic maturity. Although the effects of hydrostatic pressure are more complicated, it appears to impede the increase of organic maturity in this experimental study. Strain seems to be more important than stress although it is still hard to respectively distinguish their effects on organic maturity by experiment. Although mechanisms of coaxial deformation promoting coalification are not clear yet, flattening of existing pores and mechanical rotation of aromatic lamellae are not likely to be the principal mechanisms. The possible origin may be that coaxial deformation promotes balance reaction equation of coalification to its positive direction.