A Method of Favorable Source Rock Evaluation and Prediction: A Case Study From Zhahaquan Oil Field, Qaidam Basin (Nw China)

Abstract

In recent years, tight oil reservoirs have been found in the upper Ganchaigou Formation (Neogene) of Zhahaquan area, Qaidam Basin, but the source rock–reservoir relationship is unclear and the favorable source rock identification and prediction method need to be built urgently. Based on the experimental data of source rock samples in the study area, it is found that there are a lot of differences between favorable and useless source rocks such as color, degree of redox, salinity, paleo-water depth, carbonate content, TOC, and sedimentary environment. Moreover, after analyzing logging responses of source rock, ΔGR and Th/U are selected to calculate TOC because the two parameters are most sensitive to organic matter abundance. Furthermore, we found that the source rocks in the shallow lake area and beach bars are longitudinally superimposed on each other, and this combination is beneficial to form high-class source rock–reservoir collocation. And, the distribution of source rocks in shallow lake area is basically parallel to the lake shoreline and is consistent with the strike of beach bars. This method can be applied to favorable source rock identification and prediction of different types of areas.