study on shallow water delta provenance, sedimentary architecture and reservoir quality differences--a case of the Chang 3 member of Yanchang formation in Huachi area of Ordos Basin

To address the controversial and insufficient understanding of the source, sedimentary architecture and reservoir quality differences of the Extension Formation in the Huachi area of the Ordos Basin. This paper is based on the analysis of heavy minerals and their assemblage characteristics, cathodoluminescence imaging of quartz grains, zircon U-Pb geochronology (LA-ICP-MS). It also combines the analyses and test data of core, logging, scanning electron microscope, cast thin section, high-pressure mercury injection (HPMI), constant-rate mercury injection (CRMI) and so on. This basic principles and methods of sedimentology, stratigraphic stratigraphy, sedimentary basin analysis and reservoir sedimentology have been applied to systematically study the relationship between the provenance directions, provenance types, sedimentary system spreading, sedimentary configuration, and reservoir quality in the Chang 3 member of the Yanchang Formation in the study area. The study shows that the Chang 3 of the Huachi area is located in the sedimentary centre of the lake basin, and is influenced by provenance from both the northeast and southwest directions, and is in a mixed-source area along the Qingcheng-Heshui area; The area develops a delta front subfacies, and underwater distributary channel is the main microfacies. The single sand body has three vertical combination modes: downcut superimposed type, superimposed contact type and mudstone separated type, and three lateral combination modes: side cut superimposed type, butt type and mudstone embedded type. The delta front in the study area has an evolutionary pattern of advanced accumulation and backward accumulation, and the single sandbody of the tangential and overlapping relationship developed in the late progradation stage has the best connectivity, with good pore throat structural characteristics and good reservoir quality. In conclusion, under the background of shallow water, low accommodation space, rapid uplift-slow curtain settlement tectonics, the direction, proximity, and type of the source of shallow-water delta are the key factors influencing the distribution of sedimentary micro-phase, and also the material basis for the sedimentary configuration and reservoir quality.