Diagenesis And Pore Evolution Of The Middle-shallow Layer In The Northern Songliao Basin

On the basis of completely collecting the test data of the middle-shallow of Northern Songliao Basin, we have done more tests and given a further study to diageneses, pore evolution and the law of regional diagenesis of the middle-shallow layer in the northern Songliao basin.Diagenesis environment analysis includes temperature, pressure and fluild fields. The oil production, temperature and pressure test of 1591 exploration wells show that the geothermal gradient has the characteristics of lower in north higher in south and lower in west higher in east in Songliao basin. The geothermal gradient in eastern southeast uplift is the highest and can reach 6℃/100m, while that in western slope and northern pour area is the lowest, less than 3.7℃/100m. The formation pressure acquired by calculating intervaltravel time data of 1389 exploration wells show that the overpressure of Qing1 member distributed mainly in the central depression, and the excessive pressure in Gulong depression can reach 14 Mpa.In the diagenesis respect, by using homogenization temperature of fluid inclusions,Rovitrinite reflectance,pollen-color TAI,chromatography-mass spectrometry,pyrolysis analysis,determination of organic acids,X-ray diffraction (XRD),thin sections,scanning electron microscope(SEM),electron probe,casting thin sections,the diagenesis and porosity evolution of the mid-shallow formations in the north of Songliao basin are studied.The result indicats that the diagenesis of the mid-shallow formations in this basin diagenesis may divide into early diagenetic phase A,early diagenetic phase B,middle diagenetic phase A1,middle diagenetic phase A2 and middle diagenetic phase B(two stages and five phase)。The diagenesis of the entire mid-shallow is not too strong.In the mid-shallow formations,there are the primary pore, and secondary pore ,as well。The later formed by the atmospheric precipitation eluviation and the corrosion of the organic acid to the reservoir.The secondary pore mainly grown in the early diagenetic phase A, and approximately composes 24.8% of the total proes.According to the characteristic of the diagenesis evolution , the northern part of Songliao Basin can be divided into nine diagenesis zones.In this Basin , the diagenesis of the Eastern diagenesis zone is relatively stronger, but the west is weaker.The main reason for this difference is that the erosion occurred in the eastern region and the temperature gradient is higher than those in the west.