Sedimentery Environment And Sedimentary Of Chang-3 Oil Slice Of Yanchang Formation In Easten Gansu, Ordos Basin

Longdong area is located in the south of the Shanbei slope, one of the secondary tectonic units of Ordos Basin, its main oil-bearing bed is the Triassic, Chang-3 oil beds take on a good exploration prospect. Based on lithology, sedimentology Basin Dynamics and so on, using kinds of analysis and testing methods, the sedimentary faces of Chang-3 oil beds which belong to Triassic Yanchang Formation in Longdong area are studied well.The profiles measured by sedimentary rock, paleocurrent direction and provenance, sedimentary systems and depositional facies of the Upper Triassic Yanchang Formation, Longdong region in the southwestern Odors basin are studied. Temporal and spatial distribution of the source-reservoir-cap assemblages are also discussed in this paper, based on field word of geological survey and measurements of outcrops, observation and description of cores, analyses of drilling and logging data, light and heavy minerals in sandstones, observation and identification of thin-sections. Many outdated theories and new technological methods related to sedimentology, petroleum geology, lithofacies and paleogeography, geophysical logging are used in the paper.Research on paleocurrent directions and provenances indicate that southwest direction is the primary paleocurrent and northwest is the secondary one, whereas southeast and northeast are the accessory paleocurrent directions. The Ningxia, Liupanshan, Longxi and Qinling ancient lands which are surrounding the southwestern edge of Odors basin, are the dominating provenances for the Chang-3 slice of the Upper Triassic Yanchang Formation, Longdong Region. Provenance for the northeast part in the study area might come from the Liuliangshan and Yinshan ancient lands located in northeast of Odors basin,which may be the secondary provenance for the Yanchang formation, and the provenance for the northwest part coming from the Alashan ancient land is low-grade metamorphic rock and sedimentary rock.Use of the facies marker such as lithology, sedimentary structures, fossils, particle size distribution, log-phase analysis and profile structure of analysis of, etc, it is thought that Chang-3 oil beds contain meandering river delta facie, braided river delta facie and lake facie. Of these facies, there exit meandering river delta front subfacies, meandering river pre-delta facie, braided river delta front subfacies, braided river pre-delta facie, shallow lake facie, and can be more identified diversified sedimentary microfacies such as underwater distributary channels, mouth bars, distal bars, subsea natural barriers and crevasse splays, sand sheets, separate inter-bars, the former delta muds and shallow lake muds and so on.