Quantitative evaluation of sandstone carrier transport properties and their effects on hydrocarbon migration and accumulation: A case study of the Es32 in the southern slope of Dongying Depression, Bohai Bay Basin

Abstract

Sandstone carrier transport property evaluations are of great significance for hydrocarbon migration and accumulation analysis, but quantitative characterization and case studies are insufficient. In this article, a new parameter, relative transport index (RTi), is defined to quantitatively evaluate the capability of a sandstone carrier to transport hydrocarbon. The example of the middle sub-member of the third member of Eocene Shahejie Formation (Es32) in the southern slope of the Dongying Depression was first delineated into different sub-units based on the fourth-order sequence boundaries for a more detailed evaluation. The sandstone permeability was estimated by combining core-plug measurements with well logging to obtain more available data. The percolation characteristics of different models were analyzed to determine the total equivalent permeability of the carrier unit and were then combined with the inclination of the carrier to define and quantify RTi. This paper also characterized the hydrocarbon migration pathways and corresponding migration intensity based on the hydrocarbon occurrences and eventually revealed the relation between RTi and hydrocarbon migration and accumulation. The results show that the hydrocarbon migration pathways are mainly distributed in the regions with a relatively high RTi value. The continuous increase in RTi corresponds to the favorable direction of hydrocarbon migration, and the hydrocarbon migration can also occur in the direction in which RTi decreases slowly. The combination of all sub-units of hydrocarbon migration pathways formed three main migration directions (MMD) within the Es32 carrier unit. Moreover, the RTi value of the carrier unit is positively correlated with the corresponding hydrocarbon migration intensity, the strongest hydrocarbon migration occurred in the direction MMD2, and the hydrocarbon migration intensities that occurred in Es322, Es323, and Es324 sub-units are significantly stronger than those that occurred in other sub-units. The Wangjiagang Step-fault Zone (WSFZ) with continuous delta sandstone mainly acted as the lateral conduits for the long-distance hydrocarbon migration, and the disparity in migration intensities along the three MMDs resulted in different scales of hydrocarbon accumulation in Es32 at the edge of the southern slope.