LAUSR

Abstract Petroleum exploration in the Ordos Basin gradually expanded to the edge of the basin, but encountered difficulties on the southwestern edge. Compared with mature exploration areas inside the basin, the nature of reservoir fluids in the southwestern area is more complex. In order to better understand the oil/gas system in this area, this study conducted a detailed research on the geochemical characteristics of potential source rocks and reservoir fluids in this area. The results show that although the Chang 7 oil group in the study area developed thicker mudstone and has a high abundance of organic matter, the low degree of thermal evolution limits its hydrocarbon production. The Chang 8 oil in the study area is the result of lateral migration of products from mature source rocks inside the basin, which can be explained by the similar biomarker characteristics and gradually changing nitrogen compounds between them. Anaerobic biodegradation is an important factor that complicates the fluid properties in the study area. It not only thickens part of the oil, but also produces secondary biogenic natural gas, mainly methane.