Используйте новое ядро :)
Bitrix\Main\Loader::includeModule('sale');
$orders = Bitrix\Sale\OrderTable::getList([
'filter' => [
'PAYED' => 'Y'
],
'group' => ['USER_ID'],
'select' => ['USER_ID', 'CNT'],
'runtime' => [
new Bitrix\Main\Entity\ExpressionField('CNT', 'COUNT(*)')
]
])->fetchAll();