public partial class MainForm : Form
    {
        IniFile ini;

        Assembly assembly = null;
        Type t_ora_connection = null;
        Type t_ora_param_collection = null;
        Type t_ora_oracledbtype = null;
        
        object obj_ora_connection = null;   

        public enum MyOracleDbType
        {
            BFile = 101,
            Blob = 102,
            Byte = 103,
            Char = 104,
            Clob = 105,
            Date = 106,
            Decimal = 107,
            Double = 108,
            Long = 109,
            LongRaw = 110,
            Int16 = 111,
            Int32 = 112,
            Int64 = 113,
            IntervalDS = 114,
            IntervalYM = 115,
            NClob = 116,
            NChar = 117,
            NVarchar2 = 119,
            Raw = 120,
            RefCursor = 121,
            Single = 122,
            TimeStamp = 123,
            TimeStampLTZ = 124,
            TimeStampTZ = 125,
            Varchar2 = 126,
            XmlType = 127,
        }

        private void MainForm_Load(object sender, EventArgs e)
        {
            #region выбор библиотеки
            s_temp = ini.IniReadValue("ConnectSection", "version");
            if (!string.IsNullOrEmpty(s_temp))
            {
                string s_dir = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
                
                switch (s_temp)
                {
                    case "9":
                        s_dir += "\\Ora9\\Oracle.DataAccess.dll";
                        break;

                    case "11":
                        s_dir += "\\Ora11\\Oracle.DataAccess.dll";
                        break;
                }
                assembly = Assembly.LoadFrom(s_dir); 
            }
            #endregion

            string s_login = ini.IniReadValue("ConnectSection", "login");
            string s_pass = ini.IniReadValue("ConnectSection", "pass");
            string s_alias = ini.IniReadValue("ConnectSection", "alias");

            if (!do_connect(s_login, s_pass, s_alias))
            {
                  this.DialogResult = System.Windows.Forms.DialogResult.Cancel;
                  this.Close();
                  return;
            }
            ...
       }

        private bool do_connect(string s_login, string s_pass, string s_alias)
        {
            t_ora_connection = assembly.GetType("Oracle.DataAccess.Client.OracleConnection");
            t_ora_param_collection = assembly.GetType("Oracle.DataAccess.Client.OracleParameterCollection");
            t_ora_oracledbtype = assembly.GetType("Oracle.DataAccess.Client.OracleDbType");

            obj_ora_connection = assembly.CreateInstance("Oracle.DataAccess.Client.OracleConnection");

            bool b_result = false;
            string s_con = "User Id=" + s_login +
                           ";Password=" + s_pass +
                           ";Data Source=" + s_alias;

            MethodInfo mi_set_conn_str = t_ora_connection.GetMethod("set_ConnectionString");
            MethodInfo mi_state = t_ora_connection.GetMethod("get_State");
            MethodInfo mi_open = t_ora_connection.GetMethod("Open");

            Object[] o_arr = new Object[1];
            o_arr[0] = s_con;

            mi_set_conn_str.Invoke(obj_ora_connection, o_arr);           //добавили строку подключения
            
            try
            {
                mi_open.Invoke(obj_ora_connection, null);               //открыли соединение
                
                if ((ConnectionState)mi_state.Invoke(obj_ora_connection, null) == System.Data.ConnectionState.Open)     //проверили состояние подключения
                {
                    Append_Log("Подключение к БД: " + System.Data.ConnectionState.Open.ToString());
                    b_result = true;
                }
            }
            catch (Exception ex)
            {
                Append_Log(ex.ToString());
            }            
            
            return b_result;
        }

        private DataTable GetDataFrom_Oracle4(
                                                int i_s1,
                                                int i_n1,
                                                int i_n2,
                                                DateTime dt                                                                                                
                                                )
        {

            Type t_ora_command = null;
            object obj_ora_command = null;

            try
            {
                string s_query = "select " +
                                 [вырезано цензурой]
                                  "where  a.s1 = :P_S1 " +
                                 "and    a.n1 = :P_N1 " +
                                 "and    a.n2 = :P_N2 " +
                                 "and    a.dd_mm_yyyy = :P_DD_MM_YYYY " +
                                 "order by 1,2,3";                                                                  

                t_ora_command = assembly.GetType("Oracle.DataAccess.Client.OracleCommand");
                obj_ora_command = assembly.CreateInstance("Oracle.DataAccess.Client.OracleCommand");

                MethodInfo mi_set_cmd_text = t_ora_command.GetMethod("set_CommandText", new Type[] { typeof(System.String) });
                mi_set_cmd_text.Invoke(obj_ora_command, new object[1] { s_query });                                                     //засунули строку запроса

                MethodInfo mi_set_connection = t_ora_command.GetMethod("set_Connection", new Type[] { t_ora_connection });
                mi_set_connection.Invoke(obj_ora_command, new object[1] { obj_ora_connection });

                MethodInfo mi_set_commandtype = t_ora_command.GetMethod("set_CommandType", new Type[] { typeof(System.Data.CommandType) });
                mi_set_commandtype.Invoke(obj_ora_command, new object[1] { System.Data.CommandType.Text });

                MethodInfo mi_bindbyname = t_ora_command.GetMethod("set_BindByName", new Type[] { typeof(bool)});
                mi_bindbyname.Invoke(obj_ora_command, new object[1] { true });

                MethodInfo mi_get_parameters = t_ora_command.GetMethod("get_Parameters");
                object obj_ora_param_collection = mi_get_parameters.Invoke(obj_ora_command, null);             

                MethodInfo mi_param_add = t_ora_param_collection.GetMethod("Add", new Type[] { typeof(System.String), t_ora_oracledbtype, typeof(System.Object), typeof(System.Data.ParameterDirection) });

                object obj_ora_param_s1 = mi_param_add.Invoke(obj_ora_param_collection, new object[] { "P_S1", MyOracleDbType.Int32, i_s1, ParameterDirection.Input });
                object obj_ora_param_n1 = mi_param_add.Invoke(obj_ora_param_collection, new object[] { "P_N1", MyOracleDbType.Int32, i_n1, ParameterDirection.Input });
                object obj_ora_param_n2 = mi_param_add.Invoke(obj_ora_param_collection, new object[] { "P_N2", MyOracleDbType.Int32, i_n2, ParameterDirection.Input });
                object obj_ora_param_dd_mm_yyyy = mi_param_add.Invoke(obj_ora_param_collection, new object[] { "P_DD_MM_YYYY", MyOracleDbType.Date, dt.Date, ParameterDirection.Input });

                MethodInfo mi_executereader = t_ora_command.GetMethod("ExecuteReader", new Type[] { });
                object obj_ora_reader = mi_executereader.Invoke(obj_ora_command, null);

                DataTable DT = new DataTable();
                DT.Load((IDataReader)obj_ora_reader);

                obj_ora_param_collection = obj_ora_param_s1 = obj_ora_param_n1 = obj_ora_param_n2 = obj_ora_param_dd_mm_yyyy = obj_ora_reader = null;

                return DT;
                
            }
            catch (Exception asc_exc)
            {
                Append_Log(asc_exc.ToString());

                return null;
            }
            finally
            {
                if (obj_ora_command != null)
                {
                    ((IDisposable)obj_ora_command).Dispose();
                }                
            }
        }        

            MethodInfo mi_set_conn_str = t_ora_connection.GetMethod("set_ConnectionString");

            MethodInfo mi_set_conn_str = t_ora_connection.GetMethod("set_ConnectionString",new Type[] { typeof(System.String) });

using (OracleCommand cmd = new OracleCommand(s_query, oc))
{
     cmd.CommandType = CommandType.Text;
     cmd.BindByName = true;
     ...
}