Recognition of the Lower Limit of Reservoir Physical Properties
Authors: Dai Jinyou , Wang Yang , Wang Rui , Lin Lixin 
Published: September 2020

Abstract
The lower limit of reservoir physical properties is an important parameter for identifying the reservoir and determining the effective thickness in the reserve evaluation, and it is also an important basis for selecting the test interval in the oilfield exploration and development. In view of the basicity and necessity of studying the lower limit of reservoir physical properties, related determination methods have been the research hotspots of reservoir engineers. Existing research results show that the lower limit of the reservoir physical properties is determined under the established process technology conditions, but the lower limit of the reservoir physical properties changes with the development of oil and gas extraction technology. As the basis of effective thickness determination and reserve calculation, the sole determination of the lower limit of the reservoir physical properties is acceptable, and its changes or uncertainties are difficult to understand. Understanding the root cause of this contradictory problem theoretically is of great significance to further research on the lower limit of reservoir physical properties. Therefore, from the perspective of percolation, the author reunderstands the lower limit of the physical properties of the reservoir on the basis of systematically sorting out the difference in percolation capacity of pores of different sizes in the reservoir. The results show that: ①There are three types of lower limit of reservoir physical properties, including the lower limit of theoretical physical properties, the lower limit of producing physical properties, and the lower limit of filling physical properties. Among them, the lower limit of theoretical physical properties is the minimum effective porosity and minimum permeability of the reservoir capable of storing and percolating fluid, and its size depends on the geological conditions of the reservoir; the lower limit of producing physical properties is the minimum effective porosity and minimum permeability of a reservoir that can store and percolate fluid under production conditions, and its size depends on both the reservoir geological conditions and the production conditions of the reservoir; the lower limit of filling physical properties is the minimum effective porosity and minimum permeability of a reservoir that can store and percolate oil and gas under the state of reservoir forming, and its size depends on both the reservoir geological conditions and the reservoir forming conditions. Among the three, the lower limit of theoretical physical properties is the smallest, and the lower limit of producing physical properties and the lower limit of filling physical properties are relatively large. ②At present, the lower limit of reservoir physical properties is mainly determined based on core physical property analysis, oil test and production test data, therefore, it should be the lower limit of producing physical properties. And the lower limit of producing physical properties is closely related to the production conditions, so it is uncertain. On the contrary, the lower limit of theoretical physical properties and the lower limit of filling physical properties are irrelevant to production conditions, so they are certain. ③The study of the lower limit of reservoir physical properties should be based on the theoretical lower limit and the filling lower limit, while the producing lower limit can reflect the changes in production conditions and can be used as a dynamic index to measure oilfield development, but it should not be used as the focus of research on the lower limit of reservoir physical properties.