COMPARISON OF POST-SEDIMENTARY ALTERATIONS OF OIL-, GAS- AND WATER-BEARING ROCKS.

One of the productive horizons (17th) of north Sakhalin has been studied. The areas within and beyond oil and gas pools, near the top and at the flanks of structures were compared with areas where the horizon under study was water-bearing. The rocks were least transformed by secondary processes within oil accumulations, where a sudden increase was observed in the content of feldspars and accessory minerals (epidote, ilmenite and sphene) which had not undergone intrastratal solution. Inside gas pools, however, no deceleration of epigenesis has been observed. This points to a more recent (post-Pliocene) accumulation of gas, whereas the first oil migration in these Miocene strata occurred in the Upper Pliocene, according to the hampered epigenesis. [ABSTRACT FROM AUTHOR]