Sedimentary characteristics of braided stream-braided fan of Shawan Formation in Chunfeng Oilfield, northwest margin of Junggar Basin, China

摘要

On the foundation of the geological background, textural maturity analysis, compositional maturity analysis, mudstone color index study, and other provenance research approach were fully made use of during this study to make certain the provenance of Shawan Formation in Chunfeng Oilfield. Provenance analysis of the Shawan Formation in Chunfeng Oilfield, conducted as the first stage of this study, revealed that the main provenance direction changed from northeast to northwest gradually, with a little fluctuation, while Shawan Formation was deposited. And then synthetically using seismic data, log data, and drilling data, according to petroleum geology and reservoir sedimentology, this study analyzed the sedimentary facies indicators, single-well facies, and logging facies in Shawan Formation; clarified the distribution of the sandbodies; and reached new insights on the types of the sedimentary facies of Shawan Formation in Chunfeng Oilfield. The research indicated that braided streams were developed during the deposition of the first member of Shawan formation and in the following two periods where braided fans became dominant little by little. These three microfacies, braided channel, channel bar, and braided plain, make up a typical stacked upward-fining cycle in the braided stream system. And the braided streams flowed from the northwest to the southeast in the research region, while the first member of Shawan Formation was formed. While the second member of Shawan Formation was deposited, the braided streams shrank gradually, and the braided fan coming from the northwest began to grow, with the flow direction moving from the northwest to the northeast. From the upstream to the downstream, the braided fan can be divided into three subfacies, proximal fan, middle fan, and distal fan. And when the third member of Shawan Formation was developed, the area of the braided fan became even larger than ever before, covering over almost the whole Chunfeng Oilfield.