Word mailmerges can't import Excel charts so, unless you use an add-in such as the Many-to-One Mail Merge add-in by Doug Robbins at
http://bit.ly/1hduSCB, you would have to implement an approach that Word could use based on the numbers themselves. For example, it is possible to generate a bar graph (e.g. for a scale of 1-100) using field coding and text as in the 'Demo' document in the attached zip archive. Note that a fixed-width font is required for both the bars and the scale (currently 7pt Courier New). The zip archive also includes a sample output file. The field code assumes a data field named ‘Graph’, but you can change that to whatever your data source uses. To toggle the field code view on/off, press Alt-F9.