The period of hydrocarbon generation and migration of marjor source beds in the Songliao Basin fittted in with that of the montmorillonite which changedrapidly into illite(or chlorite).More than 80% oil and gas pools are distri-buted in mixed-layer clay belt and its overlying strata.After rapid dewatering of the montmorllonite

the pore characters and oil-water properties of the sourcebeds changed distinctly:oil migrated in oil phase and water was in binding phase.Newly developed micro-fractures then became the main passage of hy-drocarbon migration.The diagenesis of the clay minerals and the reaction of organic matter to-wards hydrocarbon conversion of the source rocks played an important role insandstone diagenesis.It has been proved by study that the development of car-bonate

SiO

2

authigenic clay minerals

the secondary pores in the sandstone and the diagenesis of clastic minerals bore close relation in origin to the above mentioned reaction products.