using (OracleConnection conn = new OracleConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString))
{
    OracleCommand command = new OracleCommand("update some_table set field1 = :field1, field2 = :field2 where field0 = :field0", conn);
    command.Parameters.Add("field0", OracleType.Number).Value = 1;
    command.Parameters.Add("field1", OracleType.VarChar).Value = "11";
    command.Parameters.Add("field2", OracleType.DateTime).Value = null;
    command.Connection.Open();
    command.ExecuteNonQuery();
}