sorting query_post

Hey there,
I just want to sort the posts by a custom field in the wp_post table named event_date (mysql->datetime) the filter_where returns the correct week by a number. The orderby and order argument does’t work as well as an filter_orderby. Is there any other solution to sort the query_post or the returning object?!

function filter_where($where = '') {
		$week = date("W");
		$week = $week + $_SESSION['count'];
	        $where .= " AND event_week =".$week ;
	    return $where;
	  }
add_filter('posts_where', 'filter_where');

query_posts(array('post_type'=>'portfolio', 'paged'=>$paged,
'portfolio-category'=>$port_cat, 'posts_per_page'=>$port_num_fetch));

I’ve tried it with

query_posts(array('post_type'=>'portfolio', 'paged'=>$paged,
'portfolio-category'=>$port_cat, 'posts_per_page'=>$port_num_fetch,
'orderby =>'event_date', 'order'=>'DESC'));

and

function filter_orderby($orderby = ''){
	$orderby = 'event_week';
	 return $orderby;
	 }
function filter_order($order = ''){
	$order = 'ASC';
	return $order;
	}

// ORDER BY
add_filter('posts_orderby','filter_orderby');
add_filter('posts_order','filter_order');