Research Of High-Resolution Sequence Stratigraphy And Sandbody Distribution In Sequence Stratigraphic Framework Of Yanchang Formation In Fuxian

Ordos basin, which contains abundant petroleum resource, is a superimposed cycles cratonic basin in China. The Yanchang Formation of Triassic is not only researched early, but also the first strata developed in the basin. It has been a primary target strata for oil and gas before many years ago. However, the exploring degree of the reservoir of Yanchang Formation in Fuxian was relative low, the studies on sedimentary facies and high-resolution sequence stratigraphy were not exact enough and need an improvement.Based on the theories of sedimentology, high-resolution sequence stratigraphy and petroleum geology, the author has researched the sedimentary facies, high-resolution sequence stratigraphy and sandbody distribution in sequence stratigraphic framework of Yanchang Formation in Fuxian for the purposes talked above so as to provide important basic data for further exploration in the area.According to the lithology, sedimentary structure, paleontology and physical geology evidences, delta facies, lacustrine facies and sublacustrine fan facies, can be identified in Yanchang Formation in the study area and their microfacies characteristics have been studied respectively. The sedimentary model of delta of Yanchang Formation in Fuxian has been established.Taking the theory of high-resolution sequence stratigraphy as a direction, by comprehensive analysing of the field sections, cores, logs and other data of Yanchang Formation in Fuxian, Yanchang Formation, identified the sequence interface, can be divided into five-grade base-level cycle sequences: a super long-term sequence cycles(SLSC), 4 long-term sequence cycles(LSC), 22 middle-term sequence cycles(MSC) and several super short-term and short-term sequence cycles. Base-level cycle facies sequence and structure characteristics have been studied. According to the structure of the system tract, the super short-term and short-term cycles sequence can be generalized into three basic types: upward deepening non-symmetry (type A), upward shallowening non-symmetry (type B) and symmetry (type C); and the middle-term cycles sequence can be generalized into two basic types: upward deepening non-symmetry (type A) and symmetry (type C).According to dividing five-grade base-level cycle sequences of Yanchang Formation in Fuxian, choosing MSC interface and flood surface as isochronous stratigraphic interfaces, middle-term sequence cycle as isochronous stratigraphic unit, which is most suitable for isochronous stratigraphic correlation, isochronous stratigraphy has been correlated. The sequence stratigraphic framework of Yanchang Formation in Fuxian has been established.In sequence stratigraphic framework, sandbody genesis type and the relation between sandbody and A/S have been studied in detail. Making use of the method of sequence paleogeographic map, taking the up-rising period and down-rising period of MSC as a mapping unit, MSC paleogeographic maps of Yanchang Formation (from MSC6 to MSC21) have been mapped. And then the characteristics of sandbody distribution and time-space evolution have been particularly studied.