Unfortunately there is a shortage of worked examples on the net. As always the simplest way when using the OpenXmlSDK is to create a word document with a chart and open it within the document explorer tool.
When I've inserted charts in the past they have been inserted as a "ChartPart" within the document, which had several child part relationships to the data source and formatting and then within the documnet Body itself a "c:chartReference" referred to the chart part by id. I believe the chartReference lives underneath a graphicData.