The Geological Structure And Hydrocarbon Accumulation Difference Research In Liaohe Subbasin

Based on the geology, geophysics means and the previous research results, through thecomparation of geological structure, tectonic evolution, structure styles, elements of poolforming and distribution characteristics of hydrocarbon, the main controlling factors ofhydrocarbon deference richness in the three depression(Damintun Depression, WesternDepression and Eastern Depression) of Liaohe Subbasin were discussed.The long/short ratio of45main depressions in Bohai Bay Basin have been statisticed bythe method of geological statistics. According to the long/short ratio, these depressions can bedivided into three types: Open, Transactional and Narrow-long type. Western Depression andEastern Depression belong to Narrow-long type and Damintun Depression belongs toTransactional type. These depressions are divided into three types according to the profileshapes: Half-graben Ⅰ, Half-graben Ⅱ and Graben. Western Depression and EasternDepression belong to Half-graben Ⅱ structure, and Damintun Depression belongs to Grabenstructure.The comparation of geological structure shows that Damintun Depression and WesternDepression are broader than Eastern Depression, so there are more space for source rocksedimentation. At the same time, there are lots of High-buried hill and volcanic rocks inEastern Depression, so the space for rock sedimentation is smaller. Besides, because of thedistinction of structural evolution, Damintun Depression and Western Depression have twosets lacustrine source rocks(Es4,Es3), but the Eastern Depression has only one set of sourcerock(Es3). Therefore Damintun Depression and Western Depression have better sourcecondition than Eastern Depression, and it makes the resource abundance has the characteristicof “two depression high and one depression low”.In a depression, the characteristics of reservoir enrichment were controlled by thedistribution of oil generating sag. Most oil and gas distributed around the oil generating sag asa ring. In addition, faults’ forming phases and activity intensity make an important influenceon the oil-bearing series and reservoir’s type. In Damintun Depression, the early faults’ activity were very strong but the late faults’ activity were very weak, so the oil and gas mainlygathered in the buried hill and Es3.In Eastern Depression, the early faults’ activity were veryweak, but the inherited faults’ activity were very strong, so the hydrocarbon mainly gatheredin Es3and the upper strata. In Western Depression, there are lots of faults in all of the stage,so the oil and gas stored in various strata. Because there are few faults in Neogene strata, theNeogene oil and gas is very less.