Prediction of major source rocks distribution in the transition from depressed to rifted basin using seismic and geological data: The Guyang to Linhe Formations in the Linhe Depression, Hetao Basin, China

Abstract

Source rock prediction in the Linhe Depression is exceptionally difficult owing to inadequate data, while the process by which depressed-rifted conversion influences source rock distribution remains unclear. Thus, this study aimed to predict source rock distribution and demonstrate its influencing factors. Based on outcrop, geochemical, well log, and seismic information, a seismic methodology involving the prediction of organic facies distribution using seismic facies analysis and mudstone thickness via a seismic velocity-lithology model was applied to predict source rocks. Our study showed the suitability of this method for early exploration in basins with inadequate data. The correlation coefficient between the predicted and borehole values of mudstone was 0.94, and the relative error was <14.6%. The optimal source rocks in the second member of the Guyang Formation were encountered in new wells JHZK9, LHC1, and JH14 and accurately predicted, thereby validating our methodology. Furthermore, optimal source rocks transitioned from broad to limited distributions, moved closer to the boundary fault, and transferred from gentle slopes to deep sags during the depression to rift period. This transition dominated the distribution of source rocks. The basin type restricted the location of source rocks, and the transfer of lacustrine centers played a leading role in the distribution and differential superimposition of source rocks. Additionally, differential compression influenced source rock thickness in the second member of the Guyang Formation, while segmented variations in the boundary fault style and activity rate influenced the thickness in the second member of the Linhe Formation.