Genesis of bitumen and high resistivity water layer in Yanchang formation, Ordos Basin, China

ABSTRACT

Many oil-bearing basins in the world have found high-resistivity water layers, which brings difficulties to the identification of oil-water layers and the exploration and development of oil fields. Yanchang Formation in Ordos Basin shows complex oil-water enrichment characteristics. Oil wells and water wells are interspersed on the plane. The resistivity of water layer is higher than that of oil layer, and it is difficult to explain it with the existing theory. Taking Chang 8₁ reservoir in Yuele area as an example, the electrical, physical and oil-bearing characteristics of two oil wells (B23 and Y73) and two water wells (Y79 and Y55) in Yuele area were comparatively studied by means of extraction experiment, GC-MS analysis, thin section observation, rock pyrolysis, resistivity, and physical property test. The results show that the high resistivity of water layer in Yanchang Formation of Ordos Basin is caused by biodegradation asphalt and heavy component of residual oil after structural adjustment. Asphalt filling is the main reason for high resistivity of water layer. The residual heavy hydrocarbon after structural adjustment aggravates the high resistivity of water layer.

KEYWORDS:

• Bitumen
• high-resistivity water layer
• Yanchang formation
• Ordos Basin
• structural adjustment

Acknowledgments

We would like to express our gratitude to the State Key Laboratory of Oil and Gas Reservoir Geology for providing the experimental analysis. This study was funded by the National Natural Science Foundation of China (No.41872165) and Research and Innovation Fund for Postgraduates of Southwest Petroleum University, China (No.2019cxyb005).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [41872165,42072185]; Research and Innovation Fund for Postgraduates of Southwest Petroleum University [2019cxyb005].