CHARACTERISTICS OF FLUID INCLUSIONS AND THEIR SIGNIFICANCE FOR RESEARCH ON OIL ACCUMULATION IN THE CENTRAL BOHAI DEPRESSION

On the basis of intensive observation of a part of the core of well BZ25-1-7 in the Central Bohai depression and a full understanding of deposit fillings,the authors studied the fluid inclusions in a key core interval.The results show that secondary fluid inclusions mainly occur in micro-fractures of quartz,cements of carbonates or calcite veins.There are four types of fluid inclusion in the area:pure liquid inclusions,pure vapor inclusions,two-phase vapor-fluid inclusions and saline inclusions.Measurements of homogenization temperatures of most fluid inclusions display three stages of fluid flow:88-100℃,115-140℃ and 140-155℃,suggesting that there were at least three stages of oil/gas migration and accumulation in the Central Bohai region.According to the above-mentioned study,combined with an analysis of the burial history and thermal history,the authors think that the oil accumulation in the Central Bohai region occurred relatively late,and that the main oil migration and accumulation stage occurred since the late Guantaoan period(13 Ma).