Research On Formation And Evolution Of Mudstone Overpressure In The North Of Songliao Basin

Trough the distribution features of mudstone overpressure in north of Songliao Basin were studies. We conclude that the high value of current overpressure of K1qn mudstone in the north of Songliao Basin mainly distributes in Qijia-Gulong depression. Where the largest value is up to 15MPa and the average is about 8.8MPa.Secondly is Sanzhao depression .Where the overpressure is up to 11MPa. And the average is about 8.3MPa .From the two areas of high value to the edge of the basin. The overpressure gradually decreases and finally disappears. The high value of overpressure of K1n1 mudstone at present .Where the largest value is up to 9MPa.It mainly distributes in Qijia-Gulong depression. From the high value area to the vicinity of basin. The overpressure of K1n1 mudstone at the edge of depression gradually decreases. Until reducing to zero. The overpressure of K1qn mudstone in the northern part of Songliao Basin firstly formed in K1qn2 and K1qn3 deposition periods. Mostly of forming in the periods of K1n4. And the overpressure of K1n1 mudstone in the northern part of Songliao basin firstly formed in K1n2 deposition periods. Mostly forming in the periods of K2m2.Evolutionary process of overpressure of K1qn1 and K1n1 mudstone shows that overpressure they have not yet reached the rupture limited could not release the overpressure through themselves rupture. The overpressure release should be mainly due to faults activities. The overpressure of K1qn1 mudstone has happened three releases. And the overpressure of K1n1 mudstone has happened two breakages. Trough studies of the role of overpressure in hydrocarbon accumulation we can conclude that K1qn1 and K1n1 source rocks in late K2m in north of Songliao basin .Possess the condition of migration downward of oil and gas. The largest distance of migration downward of oil and gas from K1qn1 source rocks in late K2m .Which is up to 550m. The largest value distributes around well Shu-19 in Sanzhao depression. And in Qijia-Gulong depression. Where the distribution is also up to 538m..Mainly distributes around well Gu-67.The longest distance of migration downward of oil and gas from K1n1 source rocks in the late E sedimentary period in the north of Songliao basin .Where the distance is up to 150m..The following is in the center Qijia-Gulong depression to the west. Sanzhao depression and very few areas of Longhupao terrace. The longest distance distributes around well Ying-10.Oil and gas of K1qn1 source rocks in the late of K2m can migration downward into F,Y oil layers. Which mainly distribute Sanzhao depression. The southern and northern part of Daqing placanticline and the center of Qijia-Gulong depression, the southern part Sanzhao depression, the center part of Longhupao terrace and Chaoyanggou terrace and so on. Which part areas of them can migration downward into Saertu oil layer. Only in small part of the middle Qijia-Gulong depression in the west can migrate downward into Putaohua oil layer. But the overpressure on the east and west sides of Daqing placanticline is obviously different. Which cause the differences of the distance and horizon of migration downward of oil and gas from K1qn source rocks. Trough the contrast of formation periods of overpressure of K1qn1 and K1n1 mudstone in Songliao basin and massive expulsive period of source rocks. We can see their formation periods is earlier than oil and gas massive expulsive period by themselves. It is effective to seal the oil and gas which self-generation and self-bleeding.