Hi @snogy
I believe you can do it by using this query:
$args = array('post_type' => 'evenement',
'showposts' => 12,
'meta_key' => 'jour_de_levenement',
'meta_compare' => '>',
'meta_value' => date("Ymd"),
'orderby' => 'meta_value_num',
'order' => 'ASC'
);
I hope this helps 🙂