- Published on Friday, 30 August 2013 09:53
- Written by Tom Jeansonne
In many regions of the U.S., the proliferation of gas and liquids discovered and extracted from shale formations has created a need for rapid infrastructure development. Valves and their automation play key roles at every stage of processing and transporting the gas and fluids—from the well to the storage facilities and distribution systems. This means they are vital in providing safety to personnel, process control for operations and protection for valuable assets as well as prevention or mitigation in the case of environmental events.
Because of the new technologies driving this unprecedented shale growth, operators have an increasing number of federal, state, local and industry regulations, standards and permitting requirements to deal with, many of which are in flux and not yet clearly defined. Also, states and municipalities not traditionally challenged with the growth of rapid infrastructure or new industry are scrambling to enact their own restrictions as a reaction to pressure from the public. That public is genuinely concerned about the safety of this unconventional technology, as well as water usage/disposal and how the drilling and production might impact the environment and their communities.
Oil and gas producers are inherently safety conscious, as well as aware of the need to avoid adverse events or activities that might result in an impact on regulations. They are also familiar with the consequences of bad press and negative public opinion that any production upset would incur. Frequently these producers are in the “crosshairs” of 24/7 media coverage that can be inaccurate, incomplete and prone to sensationalism. They know their wells and the supporting equipment are often in remote areas that can’t be readily or continually monitored by field personnel. Yet these locations need to be shut-in immediately in case of an anomaly in the processes, an emergency or a spill. Often, the answer to well and process safety is an automated emergency shutdown (ESD) solution (Figure 1).
This article discusses applicability of existing and proposed regulations on these issues as well as the industry oversight that promises to have an enormous impact on onshore oil and gas wells and related activities. The article also identifies and addresses many of the current equipment technologies regarding valve automation solutions or final control elements (which are automated shutdown valves). These final control elements are an integral part of many ESDs as well as process shutdown (PSD) solutions used at wells and flow lines. Note that this article begins discussion at the automated production or flow wing valve and is not intended to address offshore well equipment (API 17D), subsea, downhole safety valves and master valves, nor should it be considered all inclusive.
NEW AND PROPOSED REGULATIONS
A quick Internet search reveals hundreds of proposed or new regulations on shale gas. It also shows many guidance/draft/amendment rules and programs by numerous governmental agencies, standards organizations, various states and local jurisdictions, the U.S. Environment Protection Agency (EPA), the U.S. Department of the Interior, the Bureau of Land Management and the U.S. Corps of Engineers, to mention a few. A handful of states currently have fracturing moratoria in place and public awareness has been raised that hydraulic fracturing fluids may be exempt from certain EPA rules such as the Safe Drinking Water Act of 2005 (unless the process uses diesel in the fracking fluids).
Meanwhile, the EPA’s New Source Performance Standard (NSPS) 40 CFR, part 60 and 63 subpart 0000 (AKA ‘Quad O’) has been approved. Quad O regulations summarily apply to “emission standards for stationary equipment” and cover many of the activities and components used in oil and gas production, particularly in newer shale infrastructure. On top of the many regulations passed or in the works, a lengthy period of time (many say two to four years) will likely be needed to seriously address the many issues raised and to create, update or amend the applicable best practices or standards.
In the meantime, many companies and organizations are responding to growing shale development concerns by taking unique actions. A growing number of shale field coalitions and organizations that share information, such as establishing “new or local” best practices and addressing issues, have been born. For example, energy companies and environmental organizations recently formed a consortium—The Center for Sustainable Shale Development. The initial focus for this group will be minimizing air and water pollution and establishing a certification process. (For more updated information on the issues, go to www.northamericashaleblog.com.)
EMERGENCY OR PROCESS SHUTDOWN
An ESD, PSD or Safety Instrumented System is a set of components, logic solvers and final control elements arranged for the purpose of taking a process to a safe state when predetermined conditions are tripped. These components typically incorporate a spring return actuator to close the valve in the event of an upset. Such a system is important in all flow situations and is especially significant when the field is remote, unmanned or where an external power source is unavailable, undependable or prohibitively expensive. Reliability and prevention are key factors for these systems. The valves and their automation often remain in a static position for extended periods of time, yet they must perform without room for error when required for immediate shutdown or diversion. If these systems did not have this level of dependability, disasters would be much more probable (Figure 2).
All ESD/PSD actuators that require a motion, a reaction or that must lock-in-last to a “trip signal” (not just a fail in place) need some type of power source to transfer that energy into a form that can drive a valve to its pre-determined ESD/PSD position or safe state. Generally that power source, in conjunction with valve type, must be established before significant automation progress can begin. Rather than simply listing the three primary energy sources, the following is a summary of the power sources or combined power solution ideas that may be found in the shale field for typical ESD/PSD actuator use. These ideas or methodologies are certainly not all inclusive, but they represent possible out-of-the-box automation solutions.
Manual power (human effort): This source can be used to generate energy, often in the form of a manual hydraulic pump which in turn can compress a spring (in a spring return actuator).
Pneumatic or gas supply to directly compress a mechanical spring: This can take the form of instrument air supply (compressed air), a gas supply derived from the media in the valve (such as natural gas), a nitrogen bottle or any suitable pressure vessel such as an air fail-safe tank.
Pneumatic or gas stored supply: This source can be used in an adequately pressurized volume so it powers an actuator through an ESD/PSD function. This can be a gas motor or other gas-powered actuator (e.g., a gas-over-oil unit.)
Hydraulic or hydraulic power unit: Direct hydraulic power, which normally requires an electrical supply to power a hydraulic pump, can compress a spring or store hydraulic energy in a storage vessel (hydraulic accumulator).
Electric (AC, DC, including solar panel derived): Pure, electrically powered units are not normally found in ESD applications, except for situations in which a charged battery storage bank provides a backup power source or when smaller, spring return, quarter- or part-turn units are involved.
Electric hybrid: Electro-hydraulic actuators typically use an electric power source to create hydraulic pressure used to compress a mechanical spring.
FAIL MODE TRIP
Automation solutions can be configured many ways to respond to a trip and ESD or PSD signal. The most common methods used in shale fields include:
Shutdown by ESD/PSD signal to a solenoid valve: The system can be remotely or locally shutdown by an electrical signal, typically through de-energizing the solenoid valve or valves.
Loss of supply pressure: This is usually a piloted control valve with functionality similar to the solenoid valve.
High- and/or low-pressure shutdown: This is often one or two pressure pilot valves (high and/or low). Pilots or pressure sensors are installed on the flowlines at various points to automatically trigger the valve shutdown in the event the preset pressure range is exceeded (which is called an Overpressure Pipeline Protection System) or falls below a given value or range. Versions of this are also available to measure pressure drop over time, allowing for temporary pressure fluctuations within a pre-determined period of time to avoid spurious trips.
High-temperature shutdown: This is often a fusible plug device or temperature sensing device that can typically vent a motive pressure.
Wireless: A newer technology is available for monitoring the valve and flow lines and transmitting an alarm or monitoring signal for position recognition in the field. Generally, wireless transmitters are not yet considered suitable for ESD on basic process control system functions.
A mix: One or more of the above methods are combined including redundant or sequentially interrelated.
SAFETY AT THE WELL—API 6A
The Christmas tree, ESD/PSD and other equipment in a shale field are subject to many factors that impact the type of valve and automation solution. For example, the Bakken wells generally produce 1,000 to 3,000 barrels per day (bpd) at pressures of 2,000 to 4,000 psig, with temperatures averaging below 200°F (93°C). By comparison, the Eagle Ford wells can produce as high as 4,000 bpd with flow pressures to 7,000 psig and temperatures to 350°F (177°C), while other fields may see less than 100 psig.
At the Christmas tree, the API 6A standard, Specification for Wellhead and Christmas Tree, generally prevails for manual and automated valve design and functionality. For ESD/PSD service, API 6A production or flow wing valves are usually reverse-acting gate valves designed for operating pressures typically ranging from 2,000 to 15,000 psig. The ESD/PSD valves on Christmas trees are normally and historically located on the production or flow arm of the tree upstream of the production choke. These wing valves and choke valves may or may not be automated, depending on ESD functionality.
When the valves are automated, some shale producers are now adding or moving the API 6A ESD valve and/or the ESD/PSD function to the downstream side of the choke to further protect downstream equipment. This is so that, should the choke or other equipment fail, such as when a choke suddenly washes out from unanticipated wear or “slugs,” alternating slugs of gas or liquid/solids downstream don’t severely damage equipment such as heat exchangers and production separators. Traditionally, at the Christmas tree, ESD/PSD-equipped API 6A valves are hydraulically powered or in some fields powered by compressed air. However, a newer development is that API 6A ball valves are gaining acceptance for some fields and applications.
There has been a substantial increase in the demand for stand-alone or manual hydraulic, self-contained shutdown systems, in part because of best practice decisions made in the field as well as the sheer volume of shale play wells with new, inexperienced or learning curve operations. It is also because of the remoteness of these shale plays (not just measured in miles, but also measured by available manpower to well count allocations or densities).
Stand-alones or manual afford ESD/PSD protection with little or no additional control or power supply infrastructure required. Self-contained, manually powered units also have at least one advantage over most traditional units in that they do not rely on external power sources. Instead, they are powered by hand-pumping a small manual hydraulic pump located at the actuator. This attribute makes them adaptable for locations where alternate power sources are not available or may be considered less dependable.
SAFETY FOR FLOW LINE VALVES—API 6D
Beyond API 6A use at the Christmas tree and the production choke valve, valves in a shale application generally are part of the gathering, processing and storage systems. The API 6D, Specification for Pipeline Valves, and many other standards such as API 598, 599, 600, 602 and ASME B16.34 apply. The quarter-turn ball valve is often found in the ESD/PSD applications as well as check, gate, plug and butterfly valves (Figure 3).
Gathering lines carry the hydrocarbons from the well to the various separation and treating facilities, then flow to intermediate storage and fiscal custody transfer stations before product is transmitted via pipeline further downstream to processing and distribution points. At all points along the way, flow lines are susceptible to rupture, overpressure, backflow or hazards that would require immediate shutdown.
Flow lines also travel to and from facilities over considerable distances, crossing rivers, interstates and highways, areas with much human activity and to locations in remote areas where there is limited infrastructure and local supervision. These flow lines need shut-in capabilities. Automated ESD/PSD valves are viable solutions to address the many potential problems that can result.
API 6A AND/OR 6D
Generally, the same technologies used near the well are available for API 6D applications. In fact, other than special valve considerations and probable power supply source availability issues, there really is very little difference in the basic automation functionality between 6A and 6D applications. The few differences—available power source, experience with the application and the total cost of ownership—can make some solutions more prevalent for certain applications (Figure 4).
Shale plays continue to be discussed as a catalyst for the United States’ effort to become energy self-sufficient. Because oil and natural gas holds the most potential for reaching that independence, the need to produce from domestic shale sources has meant a dramatic increase in the number of wells drilled and produced. With the energy industry spearheading positive safety solutions through technology, ESD and PSD valves and actuators will play a prominent role in increasing the public’s confidence in the industry’s initiatives toward safety and environmental preservation.
VALVE AUTOMATION CONSIDERATIONS AND RESULTS
Automated valves are often used to prevent or mitigate undesirable events.
In addition to reducing risk and exposure to the facility personnel, civilians and assets, the following implications and concerns should be considered:
- Preserving and protecting the environment = Operating responsibility
- Mitigation of the effects of any spill or overfill = Risk, event cost and life-cycle cost reduction
- Legal actions and resultant regulations = Lower cost and regulatory compliance
- Lower operating costs, reduction of downtime = Increased availability and efficiency gains by extended health diagnosis
- Fines, penalties and property damage claims = Lower risk and reduced operating cost
- Lost revenue, goods and production = Revenue efficiency by extended health diagnosis
- “Alarm overload,” inexperience and physical reaction time = Event mitigation and prevention
- Transportation, outside business disruption and emergency support dilution = Lower risk, event mitigation and operating cost savings
- Damaged reputation, corporate citizenship, socio-economic issues = Corporate market value
- A deterrent to product theft and better inventory control = Product loss prevention and efficiency gains
- Effect on future expansion, permits, locations or scope plans = Hidden operating value increased and reduced regulatory compliance cost