Characterization and Origin Analysis of Heavy Oil in the Western Sag of the Liaohe Basin

[Image: see text] This article systematically examines the physical characteristics, group composition characteristics, and geochemical characteristics of heavy oil in the Western Sag of the Liaohe Basin. The examination is based on the separation and quantitative analysis of crude oil and rock samples, as well as the analysis of test results from gas chromatography with saturated hydrocarbons and aromatic hydrocarbons. It also analyzes the generation mechanism and main controlling factors of heavy oil. The results show that heavy oil has low wax content (1.8–9.2%), a low freezing point (−19–38 °C), low sulfur content (0.28–0.5%), high colloid and asphaltene content, high density (0.926–1.008 g/cm(3)), and high viscosity (328–231910 mPa·s). The physical properties of the heavy oil in the same formation decrease from the depression’s edge toward its center and within the same area, and the physical properties in different formations also have an inverse relationship with burial depth. Biodegradation is the main reason for the formation of heavy oil. Based on the biodegradation degree, there are four types of heavy oil: undegraded, weakly degraded, moderately degraded, and severely degraded. The main controlling factors of biodegradation are temperature and the water environment. This study provides a method for studying the genetic mechanism of heavy oil, an approach for discovering similar genetic oil and gas, and a basis for the transformation of heavy oil field development.