The study of diagenesis

reservoir characters and the relationship between them indicates that there is a certain time conjunction relation between porosity evolu-tion and hydrocarbon reservoiring just as that between geological structure and hydrocarbon accumulation

and moreover

the former is more complicated.Therefore

the present porosity of rock samples in outcrops and holes which do notcontain hydrocarbon can not really reflect the reservoir characters of the rocks.Only the“porosity of accumulation stage”(i.e.the porosity of rocks in themain hydrocarbon migration and accumulation stage)can be one of the valuable parameters for the evaluation of hydrocarbon reservoirs.The study of diagenesis must be carried out in detail for determining the porosity of accumulation stage

so that one may clarify the history of porosity evolution.In the meantime

wemust analyze the history of hydrocarbon generation

migration accumulation and evolution

especially the relationship between the history of porosity evolutionand that of hydrocarbon evolution.