RTU Handbook

Oil & Gas

Handbook for Remote Terminal Units (RTUs)

i

1

Siemens in the Oil and Gas Industry ...........................................................................1

2

Upstream, midstream & downstream ..........................................................................3

3

4

5

6

2.1

Upstream.................................................................................................................. 3

2.2

Midstream ................................................................................................................ 4

2.3

Downstream ............................................................................................................. 4

SCADA, RTU, DCS .........................................................................................................5 3.1

Supervisory Control and Data Acquisition (SCADA)................................................ 5

3.2

Remote Terminal Unit (RTU) ................................................................................... 6

3.3

Distributed Control System (DCS) ........................................................................... 7

3.4

Overview SCADA, RTU and DCS ............................................................................ 7

Background information ...............................................................................................8 4.1

SCADA / RTU vs. DCS ............................................................................................ 8

4.2

Telecontrol system / SCADA and RTU .................................................................... 9

RTU Applications .........................................................................................................10 5.1

RTU in the sector Oil and Gas ............................................................................... 11

5.2

Further applications regarding the neighboring sectors power, water and wastewater facilities............................................................................................... 13

5.3

General requirements ............................................................................................ 14

5.4

Specific requirements............................................................................................. 14

Glossary........................................................................................................................15

i

1 Siemens in the Oil and Gas Industry For the Oil & Gas and Petrochemical Industry Siemens dedicates two sectors (Energy and Industry) with one face to the customer. We strive to be a strategic partner for end customers, EPCs and OEMs in a long-term relationship. With our process know-how, technological solutions, plant operating solutions and commercial responsibility we reduce the risks and the time it takes to complete the projects.

Siemens among the world´s leading electrical engineering and electronics companies:

1

With Centers of Competence, Regional Business Centers and local offices all over the world and especially in the cities where the decisions in Oil&Gas are made such as Houston, London, Oslo, Moscow, Abu Dhabi, Beijing, Kuala Lumpur and Singapore we provide international project support.

2

2 Upstream, midstream & downstream The process of getting natural gas or crude oil out of the ground, and to its final destination to be used, is a complicated one. It consists mostly of 3 parts: upstream, midstream and downstream.

Gas

Upstream

Midstream

Downstream

Oil

2.1 Upstream  “Upstream” (Transport & Storage) consists mainly of the following items: •

Exploration:

Exploration outlines how natural gas or crude oil is found, and how companies decide where to drill wells for it. •

Extraction

Extraction focuses on the drilling process, and how natural gas / crude oil is brought from its underground reservoirs to the surface. •

Production

Production discusses what happens once the well is drilled; including the processing of gas /  oil once it is brought out from underground.

3

2.2 Midstream  “Midstream”, it consists mainly of the following items: •

Transport:

The transport outlines how the resource is transported from the wellhead and processing plant, using the extensive network of pipelines from country to country. •

Storage:

The Storage describes the storage of oil / gas, how it is accomplished, and why it is necessary.

2.3 Downstream  “Downstream” consists mainly of the following items: •

Processing / Refining

This item deals with all processes which are necessary to achieve the final or intermediate product to be sold on the market. E.g. refining of crude oil or conditioning of gas.

•

Distribution

The Distribution focuses on the delivery of the resource from the major pipelines to the end users, whoever they may be.

•

Marketing

Marketing discusses the role that the oil / gas marketers play in getting the resource from the wellhead to the end user.

4

3 SCADA, RTU, DCS 3.1 Supervisory Control and Data Acquisition (SCADA)  A SCADA system includes input/output signal hardware, controllers, Human Machine Interface (HMI), networks, communication, database and (application) software. SCADA is a central system that monitors and controls typically a system spread out over a long distance. The bulk of the site control is actually performed automatically by a Remote Terminal Unit (RTU) or by a Programmable Logic Controller (PLC). The SCADA system for an oil or gas pipeline typically reads the measured values such as    

temperature pressure flow level

and monitors the correct operation of the system. If necessary it sends commands (e.g. for opening / closing of valves) or setpoints (e.g. for pump / compressor control) to the connected process controllers (RTU / PLC / DCS). The SCADA system may allow an operator to change the control set point for the flow, and will allow any alarm conditions such as loss of flow or high temperature to be recorded and displayed. The feedback control loop is closed through the RTU or PLC; the SCADA system monitors the overall performance of that loop. Data acquisition begins at the RTU or PLC level and includes meter readings and equipment statuses that are communicated to SCADA as required. Data is then compiled and formatted in such a way that a control room operator using the HMI can make appropriate supervisory decisions that may be required to adjust or over-ride normal RTU / PLC controls. Data may also be collected in an archive, often built on a commodity Database Management System, to allow trending and other analytical work. SCADA systems typically implement a distributed database, commonly referred to as a tag  database , which contains data elements called tags or points . A point represents a single input or output value monitored or controlled by the system. Points can be either "hard" or "soft". A hard point is representative of an actual input or output connected to the system, while a soft point represents the result of logic and math operations applied to other hard and soft points. Most implementations conceptually remove this distinction by making every property a "soft" point (expression) that can equal a single "hard" point in the simplest case. Point values are normally stored as value-timestamp combinations; the value and the timestamp when the value was recorded or calculated. A series of value-timestamp combinations is the history of that point. It's also common to store additional metadata with tags such as: path to field device and PLC register, design time comments, and even alarming information. An important part of most SCADA implementations are alarms. An alarm is a digital status point that has either the value NORMAL or ALARM. Alarms can be created in such a way that when their requirements are met, they are activated. An example of an alarm is an 5

open/close valve not reaching the defined end position. The SCADA operator's attention is drawn to that part of the system requiring attention by the alarm. In important cases, emails and text messages can be sent along with an alarm activation alerting managers along with the SCADA operator. Components of a SCADA system are:   

Multiple RTUs or outstations Main/Sub Control Center Communication infrastructure

Control Center

Server

Application

Operator Station

Engineering Station Printer

WAN

RTU 1

RTU 2

3.2 Remote Terminal Unit (RTU)  The RTU connects to physical equipment, and reads status data such as the open/closed status from a valve, reads measurements such as pressure, flow, voltage or current. By sending signals to equipment the RTU can control equipment, such as opening or closing a valve, or setting the speed of a pump.

6

The RTU can read digital status data or analogue measurement data, and send out digital commands or analogue setpoints.

3.3 Distributed Control System (DCS)  A Distributed Control System (DCS) controls a process or any kind of dynamic system at one plant, in which the controller elements are not central in location but are distributed throughout the system with each component / sub-system connected to a controller. Typically, the entire system is networked for communication and monitoring. Distributed control systems (DCSs) are used to monitor and control distributed equipment with human intervention. The processor (which is a part of the controller) receives information from input modules and sends information to output modules. The input modules receive information from sensors in the process and output modules transmit signals / commands to the actors in the field.

3.4 Overview SCADA, RTU and DCS 

Operator

Station 1

Operator Station 2

Network Control Station

SCADA Server

Engineering Station

Main Sub Control Control Center Center

Operator Station 1

Operator Station 2

Engineering Station

SCADA Server

SCADA Server

Communication Fibre O tic Transmission

SIPLUS RIC

Block Line Valve

SIMATIC/SIPLUS S7-300 and SINAUT or SIPLUS RIC S7-300

RTU

Metering Station

Custody Transfer Station

PCS7, S7-400 FH

Compressor / Pump Station

DCS

PCS7, S7-400 FH

Tank Farm

Example: Typical automation hierarchy and communication structure for transmission pipelines.

7

4 Background information To ensure that the station functions reliably, the automation system must acquire and evaluate numerous single information items even during normal operation. In the event of a fault, additional information is required to diagnose the problem quickly.

4.1 SCADA / RTU vs. DCS  Different processes require different architectures, topologies and solutions. Based on that either SCADA / RTU or DCS is used.

wide area slow process lots of simple outstations Process image up to server “real time data base” Redundancy up to server

WAN RTU protocol slow (kbit/s) various and complex Unstable, communication failures event driven time stamping, data buffer

Features local fast process automated substations Process image in AS Function blocks, CFC Redundancy in AS Communication Bus Ethernet fast (Gbit/s) transparent stable polling mode only alarm indications timed Solution

SIPLUS RIC

SIPLUS extreme

8

4.2 Telecontrol system / SCADA and RTU  Control Center

••• WAN WAN •••

CP CP CP

Connection to a control center: 

 

Serial via RS232 to external modem Leased Line  Dial Up  GPRS  Fibre Optic, Redundant, Ring structure possible Ethernet via RJ-45 connector

9

5 RTU Applications The communication backbone (fibre optic cable) can transfer such as   

Operational Data (pressure, temperature, valve position) from the RTU Voice over IP Video Data

to a Control Center. Voice and Video is directly connected to a switch on the backbone.

This solution can be used in cases where distributed processes have to be monitored and controlled, functions previously available at the higher control level are distributed or implemented on site, stringent dielectric strength and electromagnetic compatibility requirements must be met, a real-time-capable system is required, noise immunity is very important. • •

•

• •

The System performs the following tasks: Remote indication Monitoring Safe Remote/local control Processing of measured and metered values • • • •

10

5.1 RTU in the sector Oil and Gas  RTUs are used for Monitoring and control of valve stations Communication for compressor stations Flow calculations at metering station sites Supervisory and automation of  Gas wells  Oil wells  Injection sites of gas or water Tank farms • • • •

•

Example: Oil Well

Example: RTU concept for wellheads 11

Control Center

WAN RTU 6

RTU 1

M

RTU 2

M

RTU 3

M

RTU 4

M

8...32 km

5...20 miles

RTU 5

M

M

M

M M

Transmission Pipeline

Example: Valve Stations/ Metering Stations along pipelines

Example: RTU concept for valve stations along pipelines

12

5.2 Further applications regarding the neighboring sectors  power, water and wastewater facilities  • • • •

Automation of process and potable water wells Monitoring of rain basins Control of pump stations Supervision of auxiliaries

Example: Water Injection

13

5.3 General requirements  • • • • • • • • •

Operation over a wide temperature range Norm-compatible protocols, interoperability Low power consumption Rugged, field-ready construction Field-side surge protection Local storage of monitored, measured and calculated data Expandable hardware and software Broad communications capabilities; Reports-by-Exception High levels of data security

5.4 Specific requirements  

Monitoring 0 – 16 DI for block valve positions, level alarms, scraper detection, etc.  8 – 16 AI for pressures, temperatures, flows  AGA 3 for flows  Local storage for test data   time series of AI data  test duration approx. 1 day  data sampling in 2 – 30 secs intervals



Control few automation functions  max. 2 control loops (production flow, lift injection flow)  0 – 16 DO for block valves control 



ESD (Emergency Shutdown) close safety valve in case of emergency (e.g. pipeline leakage)  software solution or hardwired solution depending on requirements 

14

6 Glossary AS BLV CFC DCS ESD MCC OS PLC RTU SCADA SCC VoIP WAN

Automation System Block Line Valve Continuous Function Chart Distributed Control System Emergency Shutdown Main Control Center Operator Station Programmable Logical Control Remote Terminal Unit Supervisory Control and Data Acquisition Sub Control Center Voice over IP Wide Area Network

15