If you have multiple categories, then you can easily create separate portfolio pages for each category.
To do so, first create a new page, title it, and select the portfolio template.
Then create a custom field and enter query_args in the name field, and cat=1 (for example) in the value field.
Note: If your Custom Fields section is not showing, then it is probably disabled by default in your WP install. To enable it, click the “Screen Options” tab at the very top of the screen and check “Custom Fields”. Once you do this, scroll to the bottom until you see the Custom Fields section appear.
Replace the number “1” with the category ID that you want to use and it will show only the category that you added in the value field.