Study on sedimentary evolution characteristics and sand body distribution law of regressive fan delta

The determination of sedimentary facies and the fine division of sedimentary microfacies are of great significance for oil and gas exploration, it not only helps to find new blocks of oil and gas potential, but also points out the direction for the fine development of old oilfields. Taking the Shahejie Formation in Huanghua Depression as an example, the sedimentary environment and sedimentary model were studied by comprehensive utilization of core data, logging, seismic and analytical test data, and the following research results were obtained :

(1) Using core data to identify the development of fan delta facies deposits in the study area, and according to the type of lithofacies, the hydrodynamic conditions of the reduction fan deposition period are divided. Eight lithofacies types are identified in the study area, which are massive bedding pebbly sandstone facies, massive bedding sandstone facies, parallel bedding sandstone facies and wavy bedding sandstone facies formed under strong hydrodynamic conditions. Horizontal bedding siltstone facies, lenticular bedding siltstone facies, massive argillaceous siltstone facies and massive mudstone facies formed under weak hydrodynamic conditions ;

(2) Four types of sedimentary microfacies were identified by well-seismic combination method, and the spatial distribution characteristics of sedimentary microfacies were quantitatively characterized. That is, the source direction has the characteristics of contiguous distribution of fan delta sand bodies close to the source and dendritic distribution of sand bodies far from the source ; in the direction of vertical provenance, the lateral migration of fan delta sand bodies leads to the superposition of sand bodies. The cross-well sections along the source and vertical source reveal that the fan delta sand body is retrograded to the source area;

(3) The difference of reservoir quality is characterized by comprehensive utilization of logging and analysis test data. The study shows that there are five reservoir types in the retrograde fan delta facies, and the difference of reservoir quality is closely related to the type of sedimentary microfacies. There are also significant differences in reservoir quality within the same microfacies;

(4) Through comprehensive analysis, the development characteristics of retrograde fan delta facies sand bodies under ' model constraint and well-seismic combination ' are clarified. This kind of sedimentary model is helpful to better describe the reservoir, determine the potential block through the dominant facies, and lay a foundation for tapping the potential of remaining oil.