The Secondary Porosity and Permeability Characteristics of Tertiary Strata and Their Origin, Liaodong Bay Basin, China

Shu Jiang¹, Paul Weimer¹, Dongsheng Cai², Guanghui Zhu³, Xiaomin Zhu⁴, and Xiaolin Hu^3
1Department of Geological Sciences, University of Colorado, Boulder, CO
²CNOOC China Ltd, Zhanjiang, China
³CNOOC Research, Beijing, China
⁴Department of Geosciences, China University of Petroleum, Beijing, China

The petroleum-rich Liaodong Bay basin in northeast China consists of three depressions and two uplifts. The Liaozhong depression is the main area of oil generation. To date, production is mostly found along the Liaoxi uplift. Early exploration efforts in the deeper portion of the basin indicated that the reservoir quality decreased much. However, this study indicates that four distinct zones of secondary porosity have developed in the different depressions and uplifts. The zones of secondary porosity in the depression are relatively deeper than those depths of the same zone in the uplift. This difference is attributed to the different thermobarogeochemistry(thermal, pressure, geochemistry) field. Correlations among porosity, permeability, diagenetic stages, evolution of clay minerals, changes in pressure, and thermal maturation indicate the four distinct zones developed due to diagenetic evolution, hydrocarbon generation and development of overpressure. The development of secondary porosity zones was mainly owing to the dissolution of the carbonate cement, feldspar and lithic grains by the organic acids generated from the migrating petroleum. Overpressure, early hydrocarbon charge, and fracturing also contributed to the development of these four zones. Therefore, this study indicates that the reservoirs with good porosity and permeability are present in deeper overpressured portions of the Liaozhong depression.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas