Final Draft January 2003

Transcription

1 22 nd World Gas Conference June 1-5, 2003 Tokyo, Japan INTERNATIONAL GAS UNION Working Committee 2 "Underground Gas Storage" Report of Study Group 2B " Operating a large UGS facility in an environmentally sensitive area " Chairman/President Bert Klamer The Netherlands Final Draft January 2003

2 Main author: Bert Klamer Head Field Operations UGS facilities NAM Netherlands Sub author: Hetty Hofsteenge Facility engineer Peter Berghuis Mechanical engineer Jaap Westerhuis Process engineer SUMMARY NAM s UGS facilities form part of the Groningen capacity system and provide volume (ca m³/year) and capacity (ca m³/day) to The Netherlands and Western Europe. The role of the Groningen system is to: Act as balance provider for Volume Act as balance provide for Capacity Ramp up quickly, i.e. increase production by m³/day within one hour. This paper focuses on the environmental constraints and targets set by NAM in order to comply with the UGS licence to operate permit requirements and in order to be regarded as a prudent operator. The plant is situated in a nature reserve and as such new philosophies and technologies were developed resulting in a significant reduction in environmental and social impact together with improvements in safety, operating costs, maintainability. Areas addressed include noise, light, water quality and emissions to air. Maintenance and inspection issues relating to the new technologies are also addressed. RESUME Les stockages souterrains de gaz de la NAM font partie du système de capacité de Groningen qui fournit volume (environ milliard de m³/an) et capacité (environ 500 million m³/jour) aux Pays-Bas et à l Europe de l Ouest. Les rôles du système de Groningen sont les suivants : - Un rôle de balance en volume - Un rôle de balance en capacité - Etre capable de «démarrer» rapidement, c est à dire d augmenter la production de 120 million m³/jour en une heure Ce rapport insiste sur les contraintes environnementales et les objectifs définis par la NAM pour être considéré comme un opérateur prudent et pour obéir aux limitations du permis de construction dans le design des stockages souterrains. Les installations sont construites dans une réserve naturelle. La conséquence est qu il faut adopter de nouvelles philosophies. De nouvelles technologies ont donc été développées qui ont eu pour résultat une réduction significative de l impact sur l environnement mais aussi une amélioration nette de la sécurité, des coûts de production, de la maintenance et des relations avec le voisinage. Sont concernés le bruit, la lumière, la qualité de l eau et les émissions dans l air. Sont aussi concernés les problèmes de maintenance et des inspections où les nouvelles technologies permettent de réduire les coûts et l impact sur l environnement. January 2003 Underground Gas Storage Page 1

3 Table of Contents 1. Role of the Groningen Asset 3 2. Gas storage Norg 3 3. Design Aspects as a result of the Environmental Impact Assessment Layout of the UGS facility Norg Noise reduction Light reduction Rain water quality measurement Emissions to air Emission measurements No flaring philosophy 6 4. Maintenance and inspection Inspection Adjusting maintenance and operations in the future 9 5 Environmental Prize 9 January 2003 Underground Gas Storage Page 2

4 Operating a large UGS facility (Norg, The Netherlands) in an environmentally sensitive area The theme of this presentation is Sustainable Development as it is embedded in all aspects of our operations and the challenge, and drive to develop new techniques and philosophies. 1. Role of the Groningen Asset The mission of the Groningen Asset is to remain the prominent supplier of capacity and volume for the Dutch and Western European gas market. The Groningen capacity system currently provides volume (ca m 3 /year) and capacity (ca m 3 /day) to The Netherlands, Germany, France, Belgium, Italy and Switzerland. The system contains the large Groningen field and UGS facilities. The role of the Groningen system is to: Act as balance provider for Volume Act as balance provide for Capacity Ramp up quickly, i.e. increase production by m 3 /day within one hour The UGSes act as peak shavers. The UGS facilities were designed to cater for winter peak (at minus 17 degrees centigrade) demands given the declining reservoir pressure and capacity of the giant Groningen field (estimated ultimate recovery ca M 3 ). The two UGS facilities, Norg and Grijpskerk, are operated by NAM, a Shell operated joint venture of Shell and Exxon. 2. Gas storage Norg The gas storage in Norg makes use of a depleted gas field reservoir. The initial reservoir pressure was 327 bar. About m 3 of natural gas has been injected to restore reservoir pressure. The storage facilities consist of a gas injection plant with a capacity of m 3 /day and a gas production plant with a nameplate capacity of m 3 /day. The gas injection plant consists of two 40 MW two stage centrifugal compressors. 3. Design Aspects as a result of the Environmental Impact Assessment An Environmental Impact Assessment study was carried out prior to engineering of the UGS facilities. The study highlighted several issues that required special attention. As a result appropriate philosophies and new technologies were developed, which resulted in significant reduction in environmental and social impact together with improvements in safety, operating costs and maintainability. 3.1 Layout of the UGS facility Norg. The plant is situated in a nature reserve. Due to constraints in building height (horizon pollution) and depth (due to an underground river) the plant had to be designed on a very large plot. Furthermore the location of the nearby picturesque village of Langelo had a big influence on the layout and design. During the design of the UGS facility intensive consultation took place with local residents and permit granting authorities over the design for optimal inclusion of the plant in the existing rural structure and landscape. This eventually resulted in the implementation of the so-called Lane concept: all building are located in a straight line when viewed from the village. This means that the plant has less visual exposure for local residents. In addition a large hill with shrubs and trees was constructed between the village and the UGS plant to further minimise the visual impact from the village. The site also has a animal crossing in order to allow indigenous animals and insects to cross the site, which is otherwise enclosed by fencing, roads and agriculture land. The flare stack is a mere 40 meters high instead of the originally intended 120 meters. January 2003 Underground Gas Storage Page 3

5 In order to reduce the height of the flare the following had to be implemented: A No Flaring Philosophy. You might like to expand on this a bit A HIPPS (High Integrity Pressure Protection System). The HIPPS system consists of tight shut-off valves and necessary instrumentation which can close-in the whole gas production facility within 1,5 seconds. These 16 valves were specially designed for the UGS. The facility is divided in 26 blowdown sections to prevent high gas volumes from being blown down during maintenance and to allow phased and controlled blow down during an emergency. January 2003 Underground Gas Storage Page 4

6 3.2 Noise reduction Noise emissions from the installation may not exceed 35 db levels, measured at the fence. To meet this requirement the following measures were necessary: Special high-density insulation around the compressor piping Insulation of the compressor hall Double insulation around flowlines Careful lay-out of piping and valves Low noise fans i for the air coolers The additional costs to reduce the noise levels to the required level were % of the total project cost. Noise levels were also restricted during construction and drilling. Special low noise piling facilities drilled more then 6464 piles in the Dutch clay. Special measures were taken during drilling activities to reduce the noise to acceptable levels; a complete insulated mud plant was installed in the middle of the wellsite area and the drilling rig then moved around this mud plant to reach the required well. 3.3 Light reduction The installation light levels may not exceed 2 Lux outside the fence. Special attention is given to the position and the height of the lights to prevent light emission above 2 Lux (this is the same light intensity of a full moon). 3.4 Rain water quality measurement. The law prescribes general measures to prevent contamination of soil and water. It also includes an annual groundwater analysis and the reporting and registration of possible incidents. In order to meet this legislation a system was developed to gather, measure and report volumes and quality of the rainwater falling on the location. 3.5 Emissions to air In order to reduce the emissions to air a number of additional measures are put in place: Furnaces used for drying the silica gel absorbent were designed with low-no X burners. Low-pressure gas from tanks and other equipment is used as fuel gas (vapour return). The compressors are driven by 40 MW electric motors instead of gas turbines. This lowers emissions from the gas injection process as large (commercial) power plants have a higher efficiency then local small-scale power generation. In addition this engine increases the availability and reliability of the injection facilities and is low in maintenance costs. No flaring philosophy. During truck loading with condensate the gas returns are routed via active carbon filters to minimise environmental impact. 3.6 Emission measurements The environmental permit for the UGS refers to the Dutch Emission Guideline (Nederlandse Emissie Richtlijn, NER). Therefore compliance with this guideline forms part of the environmental permit. This guideline states that reduction of fugitive emissions will be attained by implementing a program of high frequency checks of maintenance of pumps, compressors, valves, safety valves and other accessories. The obligation of an annual leak detection test is reduced to an annual random test of 25% of the total test, if it can be proven that less then 5% of all potential leaks emit more then ppm-v of hydrocarbons. A leak detection test consists of the following elements: 1. Make inventory of all potential leaks in the installation (methane) 2. Measure all potential leaks 3. Converts potential leaks from ppm's to kg/year, according to EPA method 4. Convert to environmental impact units (EIU) and justify actions or acceptance of situation to the government. January 2003 Underground Gas Storage Page 5

7 In 1997 measurements where taken by a Belgium Company named The Sniffers using specially trained dogs to detect leaks. Dogs are now only used during subsurface transport line inspections. For surface production facilities they use special measuring devices to detect the small leaks. The Sniffers execute diffuse emission measurement for about 25 NAM surface facilities annually. The UGSes are measured once every four years. Diffuse emission measurements in 2002 were taken with specialist measurement equipment which can detect methane leaks of 10 ppm. In ,79% of potential leaks at Norg were above the leak definition of 1000 ppm. This translates to 5000 EIU's (Environmental Impact Units) of diffuse emissions annually. Measurement of continuous and discontinuous emissions A monitoring and measurement system is in place for all emission sources. Volumes of all emission sources are measured and with the use of factors translated in environmental impact units so one can compare different emission components with each other. 3.7 No flaring philosophy Norg is situated in a nature reserve and near a lightly populated area and as such has had to restrict flare capacity and flare size criteria defined by the authorities. These criteria are incompatible with excessive high relief rates and require a technique for overpressure protection in the production lines and in the compressor discharge lines, called HIPPS, to isolate the source of overpressure instead of relieving it. The HIPPS system has to ensure that the system section to be protected has been isolated from the pressure source within 1,5 seconds and that the system pressure will not exceed 110% of the design pressure. January 2003 Underground Gas Storage Page 6

8 The High Integrity Pressure Protection System (HIPPS) used is designed according to the following rules: The likelihood of the safety systems to achieve its safety functions under all conditions in a certain time interval has to be better than 10-4 failures per demand. The reaction time of the HIPPS shall be less than 2 seconds The HIPPS shall be supplemented by an overpressure relief valve The capacity of the relief valve shall be based on the flare capacity available, but not be less than 10% of the max. possible flow through the HIPPS. The flare capacity shall be based on the emergency relief requirements of the largest ESD (emergency shutdown) section. HIPPS system January 2003 Underground Gas Storage Page 7

9 4. Maintenance and inspection The inspection interval at the Norg is driven by the mandatory 6-yearly inspection of all pressure vessels, the most costly element of this are the silicagel vessels (six adsorbers installed at each UGS) to check the technical integrity (no leakage and no fractures of the internal insulation). Based on the above the first inspection at Norg is planned for 2003 and the same approach will be used as for the first inspection of the silica gel vessels at Grijpskerk (NAM s other UGS) in A full inspection of the cladding (S316) of the silica gel vessels and gunnite lining would involve removing and then changing out all silica gel contained in the vessel (regardless of the condition of the silica gel itself, as it would be prohibitively expensive to re-stack the silica gel). This would be a very costly activity (estimated cost Euro) per vessel and sub optimal use of materials (silica gel). Therefore an Inspection Strategy has been developed to remove the necessity for internal inspection. 4.1 Inspection The Inspection strategy which has been developed consist three inspection methods: Thermal paint (paint that changes colour with increased temperature) on the outside of the vessels to detect insulation leaks inside the vessel. Thermo graphic (Infrared) video, which detects insulation leaks. TOFD (Time Of Flight Diffraction), which detects cracks in material and bonding failures. The cost reduction of the three inspection methods for both underground storage locations is 10 million every 6 years. Lifetime savings accumulate to a total cost reduction of 80 million. Apart from considerable economic advantages this method also has benefits in other areas: Health and safety: it is not necessary to change out the silica gel and to work under a nitrogen atmosphere inside the adsorber. Improved Availability: it is possible to execute TOFD during production. Sustainability: silica gel can continue to used until the end of its life The 2003 TOFD inspection at Norg will be regarded as the zero measurement. Future inspection results will be compared to this and trends analysed to optimise the inspection periods and possible cost savings. January 2003 Underground Gas Storage Page 8

10 4.2 Adjusting maintenance and operations in the future The UGS facility has been designed for 250 mode switches (injection to production or vice versa) per year. The maintenance plan and strategy has been developed accordingly. As a result of the liberalisation of the gas market in Europe the use of the UGS and therefore the maintenance plans and strategies are expected to change drastically as more switches are expected. According to modern methods an optimum with respect to maintenance can be achieved by carrying out the following studies: RRM (Risk Reliability Management) RCM (Reliability Centred Maintenance) RBI (Risk Based Inspection) IPF (Instrument Protected Functions) The results of these studies will vary depending on the number of mode switches. Pre work can be done in anticipation of changes and the resulting maintenance requirements recorded in SAP NAM s administrative maintenance system. The changes to maintenance frequency can then be implemented quickly in the field if the change in mode switch frequency is realised. 5 Environmental Prize In 2000 the UGS Norg won the environmental Welstand prize. This prize is awarded for the design of a construction plan that the jury considers does most justice to its goals, namely the promotion and maintenance of rural and urban beauty in the Province. One of the main reasons for awarding this prize to Norg was the sympathetic inclusion of the UGS facility in the vulnerable river valley landscape of the Drenthe Province. Other important reasons were quoted as the attention drawn to the smallest details and architecture. January 2003 Underground Gas Storage Page 9