Sand-mudstone modeling of fluvial fan sedimentary facies: a case study of Shanxi Formation reservoir in Ordos Basin

Abstract

The sand bodies formed by braided fluvial fan deposits have a certain distinctiveness. They not only have the characteristics of fluvial facies sandbodies but also follow the distribution law of alluvial fan sand bodies. The variation law of sandbodies that are present along and perpendicular to a channel is relatively complex. Therefore, constraints in the modeling process of sand–mudstone facies of this type of reservoir are essential. This study selects the second member of the Shanxi Formation reservoir formed by a braided fluvial fan in the middle of Ordos Basin to perform sand–mudstone facies modeling. First, by studying the lithology and sedimentary structure of the area, the sedimentary characteristics and sand body distribution law of braided river fan are analyzed. Then, the original data points are analyzed, the variation function with high convergence is obtained, and the sand–mud facies model under the constraint of sedimentary facies is established using the random modeling method. Finally, the accuracy of the established random model is tested via single-well thinning, multi-well thinning, and random seed model similarity. The test results confirm that the distribution law of the sand and mudstone in the model is highly similar to that of the actual stratum. And it also conforms to the sedimentary model of braided fluvial fan. The accuracy of the model established by this method is reliable, and the method can be used to predict sand body distribution in areas with low well pattern density.