The Research About Stratigraphic Classification, Correlation And Sedimentary Facies Of Zhuang 36 Borefild In Heshui Areas, Gansu Province

In this paper, under the guide of Sequence stratigraphy and sedimentology and related disciplines theory and methodology, to study the stratigraphic division, correlation and sedimentary facies of Zhuang 36 borefild of Heshui area, Gansu Province, and summarized out the medium and short-term cycle characteristics of C₈ in this area, based on their cycle characteristics, application of core drilling core data and well log data, usage of regional marker beds, calculated the top and bottom of C₈. Inside C₈, based on its domain geologic characteristics and current stratigraphy division scenario, compared the cycle characteristics of short-term and medium term, step control, divided into single sand layer, with the distribution of main layer, determined the division and correlation, established the composite columnr profile and skeleton contrast profile of oil layer, gradually horizontal tracking and comparison, achieved the complete closure of each sub-layer, and finalized the division scenario of C₈, as subdivided into 5 sub-layers - C8₁¹, C8₁², C 8₁³, C8₂¹ and C8₂², and described the formation sand distribution regular of C₈.In general, the overall thickness of C₈ area changed little, the first order marker bed K1, K0 distributed in the whole area, under the control of the first order marker bed, cycle characteristics are apparent, interlayer thickness is large, the distribution is wide, logging traces are easily recognizable, and sublayer’s correlation accuracy is relatively high. Sandstone and oil layer are concentrated in C₈1, the thickness of C₈² sandstone layer is too thin to be the main oil exploration horizon. The general microfacies’trend of C₈1 subsea distributary channel is NW– SE. In C₈² study area, the river is less developed, which only concentrates in the central part, whose trend is still SSE, also the river piracy and cocurrent flow are not significant, which is significantly different from the previous results as there were multiple branching and cocurrent flow with the trend of NNE. Nevertheless, looking around from the peripheral and regional depositional characteristics of C₈, especially from the core observation result, it is no doubt to be braided delta front subfacies.After the observation and description of the 33 core wells in the study area, and deeply analysis and synthesis about lithology and sedimentary singenesis of C₈ oil layer, in this paper, a new braided delta sedimentary facies model of C₈ area was setup; the sedimentary facies feature of C₈ was summarized, as due to the area limited near the lake, which developed only 2 subfacies - braided delta front and predelta, but lack of delta plain subfacies during the depositional stage of C₈ oil layer, which braided delta front subfacies are mainly divided as subsea distributary channel microfacies and subsea interdistributary microfacies, with minor is mouth bar microfacies, and predelta subfacies is only a predelta microfacies, which is difficult to distinguish between deep lake with the open lake, and often clips turbidite lenses; and the distribution and evolution regular of C₈ sedimentary facies was illustrated.