Lower limit of tight oil flowing porosity: Application of high-pressure mercury intrusion in the fourth Member of Cretaceous Quantou Formation in southern Songliao Basin, NE China

Abstract

According to porosity measured by high-pressure mercury intrusion experiments and helium, and analysis of oil saturation data of 30 samples of tight formations of Member 4 of Cretaceous Quantou Formation in Rangzijing slope zone, southern Songliao Basin, the lower limit of flowing porosity of tight oil and its controlling factors of the samples were determined. By conversion between capillary pressure in reservoir conditions and capillary pressure from high-pressure mercury intrusion experiments, flowing porosity in various injection pressures in reservoir condition can be calculated. By calculating the minimum flowing porosity of oil-bearing samples and the maximum flowing porosity of the samples without oil, it is confirmed that 3.2% is the lower limit of flowing porosity in the oil-bearing samples in the study area; and the corresponding injection pressure in reservoir conditions is 0.35 MPa. If the injection pressure is higher than 0.35 MPa, tight oil can effectively flow and accumulate. The flowing porosity of tight formations and pore-throat ratio are negatively related. When the connectivity of pore-throat in reservoirs becomes poorer, higher injection pressure is needed for flowing porosity to be 3.2%. The injection pressure needed for flowing porosity to be 3.2% have a negative correlation to reservoir quality coefficient. With the reservoir quality coefficient increasing, the injection pressure needed for flowing porosity to be 3.2% has a decreasing tendency. Based on the tight oil lower limit of flowing porosity and injection pressure in reservoir conditions, the discriminant chart of effective accumulation of tight oil was set up. Key words: southern Songliao Basin, Cretaceous, tight oil, lower limit of flowing porosity