Reservoir characteristics and economic sweet classification scheme of Fuyu reservoir in Daqing Oilfield

The resources of the Fuyu reservoir in the Daqing Oilfield are abundant. Due to the unclear characteristics of reservoir and lack of scientific sweet classification scheme, it is difficult to optimize the sweet in the study area. In order to clarify reservoir characteristics and sweet selection scheme in the study area, this paper uses core physical property, XRD, casting thin section, scanning electron microscope, rock mechanics tests, high pressure mercury intrusion tests and logging data to establish the physical properties and the brittleness model of the study area., which ultimately provides a basis for clarifying reservoir characteristics and sweet screening. The results reveal ① the study area belongs to low hole-ultra low permeability reservoir, brittleness index between 0.5-0.75 and the pore structure of the reservoir in the study area can be divided into four types. Type Ⅰ reservoirs have more large-pore throats and fewer small-pore throats, with a mean porosity is more than 11% and a permeability is more than 0.7×10^-3 μm², the mercury saturation is more than 75% and the connectivity is good. Porosity of type Ⅱ reservoirs mainly locates 9%-12% and a permeability is 0.3×10^-3-0.7×10^-3 μm², the mercury saturation is more than 70% and the connectivity is good. Type Ⅲ reservoirs have fewer large-pore throats, but more small-pore throats. The porosity mainly locates 8%-11% and a permeability is 0.1×10^-3-0.3×10^-3 μm². The mercury saturation is more than 60% and the connectivity is poorer than type Ⅰ and Ⅱ. Type Ⅳ reservoirs have few small-pore throats, with a mean porosity is less than 9% and a permeability is less than 0.1×10^-3 μm², and the mercury saturation is less than 60% which have poor connectivity and permeability. ② Combine physical properties, oily and brittleness of reservoir and use gray relation method to establish the economic sweet classification standard in the study area. The comprehensive score of type Ⅰ economic sweet is more than 0.55, and the comprehensive score of type Ⅱ economic sweet is in 0.4-0.55, and the class Ⅲ economic sweet in 0.25-0.4. The non-reservoir or dry layer comprehensive score is less than 0.25. The well was verified by the classification standard and found that the standardeffectively solves the error according to the log to judge whether the reservoir contains oil. ③ Sedimentation, diagenesis, and faults interaction control the development of economic sweet. Sedimentation controls reservoir physical properties and pore structure, and diagenesis increases reservoir heterogeneity, and the existence of faults greatly affects reservoir oil. The results establish a sweet classification model to provide a scientific basis for the selection of sweet in the study area.