Depositional facies mapping based on seismic data: A case study of the 8th member of Shihezi Formation, Gaojiahe 3D block, Yanchang exploration zone, Ordos Basin

Seismic data were applied in the study of sedimentary facies distributions in the 8th member of Shihezi Formation in Gaojiahe 3D block in Yanchang exploration area, the Ordos Basin. Rock properties are the basis for the application of seismic data in sedimentological interpretation. The seismic reflection frequency in sand layers was analyzed using a time-frequency technique and based on 90° phase seismic data body. Seismic wave interfe-rence in sand layers was reduced using filtering techniques. Combining geological, well logging and seismic data, a sedimentological interpretation of strata slices with different principal frequencies was made, which helped improve the accuracy of sedimentary facies prediction. The 8th member of Shihezi Formation is mainly delta front subfacies arising from two large rivers. One underwater distributary channel goes from southeast to northwest along wells S228, S232, S204, S205, Yq2 and S216, and the other goes from east to west along wells Y218, S222, Y120 and S226. The gamma curves of sand bodies in these underwater distributary channels are bell-shaped, dentate-like or box-shaped, and are shown in the stratigraphic section as a medium-strong energy band reflection pattern. In addition, a smaller-scale underwater distributary channel was found along wells S212, Y217, S211, S210, S246 and S247 on the western margin of the study area, and featured a medium to weak energy worm-like and small patch seismic reflection pattern on a stratigraphic section.