Add as a particular role while creating an account in Drupal 7?
Adding my comment as answer. If every user is a blogger then the easiest way I see is not to have it as a separate role at all; instead assign similar permissions to authenticated user.

Or you could change the role of the user by implementing hook_user_insert():

function MODULE_user_insert(&amp;$edit, $account, $category) {
  $account-&gt;role = 'blogger';
  user_save($account, $edit = array(), $category = 'account');
}