February 2017, Vol. 244, No. 2
Features
Automated Pigging Systems Are a Tool Whose Time has Come
Shale production, for both natural gas and crude oil, is conducive to internal corrosion failures on pipeline systems. Continuous pigging programs are the most economical and practical method of reducing the risk threat for the occurrence of internal corrosion failures, maintaining effective flow efficiencies and maximizing flow throughput.
If the pipeline is not pigged frequently, the line will become susceptible to corrosive acids that eat away at the internal surface of the pipeline. According to the Pipeline and Hazardous Materials Safety Administration (PHMSA), “Approximately 299,000 miles of onshore gas transmission pipelines and 171,000 miles of onshore hazardous liquid pipelines move natural gas, crude oil and petroleum products throughout the U.S. every day.”
Corrosion from lack of pigging elevates the probability of public risk from leaking hazardous gases and liquids. This hazard can affect the environment and surrounding populations; putting them at risk for injuries and fatalities from fires or explosions caused by ignition of a leaking by-product.
Shale Play Growth Projected
According to long-term market studies, the importance of the shale gas market is not going to diminish in the future. For example, a 2011 report issued by ICF International on behalf of the INGAA Foundation, predicted in total United States and Canadian shale gas production will jump from 2010 levels of about 13 Bcf/d to 52 Bcf/d by 2035. The report also anticipates over 400,000 miles of new gathering pipe will be constructed in North America by 2035. Growth is not limited to North America; shale gas plays are also among the fastest growing production areas worldwide.
As liquids-rich unconventional resource plays continue to be developed, there are multiple challenges and implications for midstream system infrastructure, particularly around pigging and integrity. This is especially true for shale plays producing rich gas (also known as wet gas), which contain significant levels of liquefiable hydrocarbons (like ethane or propane) along with methane gas.
Liquids can accumulate at low elevation points along gathering systems where the high liquid concentrations in the gas streams cause significant issues with slugging, high differential pressures (liquids loading) and corrosion. In addition, crude oil containing high levels of paraffin and other flow reducing contaminants (frac sand, chlorides and spent chemicals) create flow restriction issues in these midstream pipeline systems. Many factors contribute to the overall performance and flow efficiency of pipeline systems, including the elevation profile, flow volumes, product quality and temperature. Each pipeline must be evaluated on an individual basis to determine its most effective pigging program.
Pigging Systems Improve Shale Play Production
An automated pigging system is defined as a method or system for staging and launching single or multiple pigs in a pre-set sequence. Such a system is typically used to address the following issues in a midstream system: wet gas line, crude oil line, fracking contamination, unpredictable fluid production, internal corrosion, enhanced safety and environmental exposure. The high number of lines to be pigged and the need to pig these lines frequently may require installation of multiple pig launchers. Automation of pigging systems offers compelling economic benefits when compared to traditional manual pigging systems. As a result, since the precedents are still undefined, producers and gathering companies are still seeking scalable solutions to these issues.
By drawing upon its experience, WeldFit Energy Group developed a horizontal automated pigging system which loads multiple pigs at one time and satisfies all four pigging functions: liquid removal, cleaning, batching and inspection. The SureLaunch™ Automated Pigging System releases any type of pig individually at pre-set intervals through use of a horizontally oriented screw jack launch system. The system also enables operators to launch a single cleaning pig, batching pig or inline inspection tool in a manual mode of operation, if desired. Although shale play pipelines are not typically regulated like transmission pipelines, the ability to continuously remove valuable liquids and maintain pipeline integrity is equal to that of transmission pipelines.
Traditional manual pigging systems are both time- and labor-Intensive. A typical pigging system requires the opening and/or closing of three major valves, the draining and venting of a barrel, and the opening and closing of a closure door. In some cases, it can take up to four hours for a single crew to load and launch a single pig, not including the time to receive and remove the pig. Beyond the time and labor constraints, there are also wear and safety considerations that must be addressed. Opening and closing valves several times a week can increase the risk of valve seat failure, thereby increasing maintenance and replacement costs. Frequent cycling of the launcher and receiver barrels can also create unnecessary safety risks that may include cyclic fatigue of the systems and additional exposure to hazardous gases that are produced in many of the shale plays.
Routine Pigging Increases Throughput
In order to prevent liquids from accumulating and to maximize production levels, routine pigging is required. Routine pigging removes liquids from the line, offers control on the volume of liquids that are removed at any one time, and sustains well production at consistent capacity. Routine pigging also removes contaminants associated with wet gas, including paraffin, asphaltenes, iron oxides, water, hydrogen sulfide and carbon dioxide. Pigging frequency should be determined based on the specific characteristics of the pipeline system. Pigging may be required as often as several times a week, or in some cases, multiple times a day. In most cases, pigging frequency should be based on flow efficiency over time, as opposed to many pigging programs that are based strictly on time.
PHMSA states that 24% of liquid transmission pipelines and 20% of gas transmission pipeline failures are caused by corrosion. Corrosion can be reduced with frequent pigging to manage the integrity of gathering pipeline systems. Increased throughput and revenue associated with efficiently operating the pipeline is measureable by the increase in percentage of flow increase. A recent case study on a natural gas gather line in northwest Oklahoma resulted in a 4.5% efficiency increase, due to pigging four times per day. The flow rate increased from 25 to 30 MMcf/d removing 1,000 to 1,00 bbl by pigging every six hours; old flow rate was 25 MMcf/d and the new flow rate is 30 MMcf/d, a 20% increase in flow rate.
Additional efficiencies as a result of frequent pigging can be attributed to improvements in reduced compression costs. As pigging frequency increases and pressure drop is minimized, less horsepower is consumed. Less horsepower equates to reduced fuel costs to power compressors.
Looking to the Future
There is every reason to expect that the scope and needs of the shale gas market will continue to grow. As the existing shale plays mature and new plays go online, increasing production flow and manpower efficiency while decreasing operating and maintenance costs will be critical keys to success. Pigging solutions such as the automated system described here can help operators meet the daily challenges encountered in the field.
The automation of pigging systems has proven to be successful in the shale plays where they can be monitored through operator SCADA and remote monitoring systems, along with operational data like line pressures and flow rates. The integration of multiple monitored data sets can assist operators with maintaining optimum flow efficiencies by comparing the theoretical differential pressures to the actual differential pressures to establish the appropriate pigging frequencies from the performance-based conditions of the pipeline system.
Author: Roxy Mounter has over 15 years’ experience in the oil and gas industry, specializing in procurement and sales. She is vice president of Sales at WeldFit Energy Group where she oversees and supports technical sales, outside sales representatives, international representatives, marketing, and estimating. She has initiated WeldFit Energy Group’s pigging technologies product lines and has opened up the market share for the company.
Mounter holds a BBA from Texas A&M University where she received a degree in Information Systems and Operations Management and completed both fields of study; Supply Chain Management (SCM) & Management Information Systems (MIS). She also obtained a Master’s of Science in Accounting from the University of Houston.
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