DECLARE @string sysname;

SELECT @string = '< search string >';

SELECT
    OBJECT_NAME(major_id) AS ObjectName, 
    USER_NAME(grantor_principal_id) AS Grantor, 
    USER_NAME(grantee_principal_id) AS Grantee, 
    p.permission_name
FROM
    sys.database_permissions p
WHERE
    OBJECTPROPERTY(major_id, 'IsMSSHipped') = 0 AND 
    USER_NAME(grantee_principal_id) = @string
ORDER BY
    OBJECT_NAME(major_id), USER_NAME(grantee_principal_id), permission_name;