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Publication - Research Publication

Unconventional oil and gas: understanding and mitigating community impacts from transportation

Published: 8 Nov 2016

Research into understanding and mitigating community impacts from transportation related to unconventional oil and gas.

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76 page PDF

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Contents
Unconventional oil and gas: understanding and mitigating community impacts from transportation
4 Traffic generation by onshore oil and gas activity

76 page PDF

2.1MB

4 Traffic generation by onshore oil and gas activity

4.1 Material quantities for well pad activities

The construction and operation of an onshore oil and gas facility requires the movement of large quantities of equipment and materials to the location of the proposed well-head, ranging from drilling equipment to concrete and water. Once its use is completed, equipment then needs to be removed from the site along with waste materials. It is assumed that oil and gas produced at a well pad site would be transported by pipeline. Well-sites could in principle be located in a wide range of settings, including rural, industrial, urban or suburban locations. In some cases, sites may need to be accessed by newly constructed site access roads as well as the existing road network.

Various pieces of equipment and batches of materials would be delivered to the site throughout the development, with the quantity determined by the scale of the operation and the phase of the process. Due to the weight and size of these items, they would typically require the use of heavy goods vehicles in order to transport them. The details of plant, equipment and materials transportation which would be required at individual sites would result from the interaction between the activities to be carried out, regulatory requirements, and the specific circumstances and constraints of the site.

In the UK, a Heavy Goods Vehicle ( HGV) is defined as a vehicle over 3,500 kg unladen weight. A Light Goods Vehicle is defined as a commercial vehicle under 3,500 kg. HGVs must not exceed 40 tonnes laden weight. Vehicles exceeding 40 tonnes laden weight are classified as Abnormal Loads and the movement of such loads requires an application process. A different definition is used in the US, with vehicles specified in eight separate classes. However, the studies reviewed as part of this project do not necessarily use the standard US definitions.

4.1.1 Hydraulic fracturing

The following is a summary of equipment used at hydraulic fracturing sites in the Marcellus Shale (eastern USA) and Eagle Ford Shale (state of Texas, USA) regions, based on observations by Rodriguez & Ouyang (2013) [13] . This represents a site during the hydraulic fracturing stage, and does not include the equipment used during the other phases, such as the drilling rigs, for vertical and horizontal wells, and excavation plant. It is assumed that a similar range of equipment would be required for development of a UOG site requiring hydraulic fracturing in Scotland. The traffic movements required to bring this equipment to and from a UOG site are set out in subsequent tables.

Table 1: Equipment used at hydraulic fracturing sites in the Marcellus and Eagle Ford shale regions

Equipment type Number of units Equipment type Number of units
Fracturing pump 14 - 16 Coiled tubing n/a
Data monitoring and recording van 1 Wireline 2
Sand chief (loading/unloading proppant) 2 Wellhead n/a
Boom truck (large forklift) 1 Frac tanks - stimulation fluid storage 10
Frac missile (low/high pressure manifold) 1 Acid tanks 1
Frac blender 1 Flow-back tanks 2
Casing pump 1 Fueling truck 1
Hydration unit 1 Water transfer pump 1
Chemical float 1 Iron truck (crane) 1
Gel mixer 1 Iron and hose trailer 1
Chemical transport 2 Parts trailer 1
High rate skid 1 Pumping skid 1
Production tank 1    

In addition to the equipment listed above, vehicle movements are required to bring materials to and from the site. Cuttings produced as a result of drilling must be removed from the site for disposal.

The process of hydraulic fracturing is reliant on the supply of water, as well as proppant (sand) and chemicals. The water can either be supplied through a dedicated pipeline or, as is more commonly the case, be delivered to the site by road tanker. During flow-back, the waste-water that returns to the surface would typically be temporarily stored at the site in retention ponds, before being transported to a waste-water disposal site.

In the Scottish context, it is likely that a mains water supply would be located sufficiently close to some well pad sites to enable water to be transferred to the site by pipeline. This is unlikely to be the case for all well pads, and site-specific issues such as barriers to securing the relevant access rights to install a temporary pipeline may prevent mains water being used at sites where this would otherwise be a viable option. It is anticipated that mains water could be used for hydraulic fracturing at a significant proportion of well pads in Scotland. This has been accounted for in this analysis by considering two scenarios - one scenario in which all water transferred to/from the site takes place by pipeline, or in the case of wastewater is re-used on site, and a second scenario in which all water transferred to/from the site takes place by road.

As highlighted below, a significant quantity of produced water from within the shale formation would require management. It is possible that a proportion of this produced water could be re-used for fracturing subsequent well stages. There is a limit to the extent of re-use of produced water, because of the inorganic salt content, and potential presence of Naturally Occurring Radioactive Materials ( NORM). The industry view is that the salinity and NORM of produced water from shale in Scotland is likely to be lower than elsewhere, because of the conditions under which the shale was originally formed. However, this cannot be guaranteed. The potential range of re-use of wastewater in Scotland has been accounted for in this analysis within the two scenarios highlighted above - one scenario in which all water transferred to/from the site takes place by pipeline, or in the case of wastewater is re-used on site, and a second scenario in which all water transferred to/from the site takes place by road.

The following provides estimations of the quantity of materials required for the operation of a 'typical' hydraulic fracturing site, based on several published sources.

Table 2: Estimations of material requirements for hydraulic fracturing

Phase Equipment / material Quantity Description / reference
Exploration Cuttings removed 140 m 3 Per well, as per Cuadrilla's forecast development scenarios [6]
Appraisal
Production Water in during hydraulic fracturing 8,400 m 3 Per well, as per Cuadrilla's forecast development scenarios [6]
1,500 - 45,000 m 3 Per well (King, 2012) [14]
3,500 - 26,000 m 3 Per well, including initial drilling (Jiang et al., 2013) [15]
1,100 - 2,200 m 3 Per stage of the fracking operation for a single well (9,000 - 29,000 m 3 per well) [6]
2 - 5 million gallons 9,000 - 23,000 m 3 Per well (United States EPA) [16]
19,425 m 3 Per horizontal gas well, median [17]
Water out (returned fracturing fluid and produced water) during hydraulic fracturing 5 - 50% of injected volume King, 2012 [14]
15 - 80% of injected fluid United States EPA [16]
9 - 35% returned water NYSDEP, 2009
20 - 40% Cuadrilla [18]
15 - 100% Schneider, 2014 [19]
Water in during refracturing 50% of water used in fracturing 4,500 - 14,500 m 3 Broderick et al. 2011 [6]
Water out during refracturing 660 - 11,440 m [3] Broderick et al. 2011
Proppant in 5% by volume of water Broderick et al. 2011
Chemicals in <1% by volume of water Schneider, A., 2014
Decommissioning & restoration No data

As illustrated in Table 2, estimations on the quantity of materials required per well vary depending on the source. For the purposes of this assessment, we have assumed the values provided by Cuadrilla to be the most applicable to UK hydraulic fracturing sites. These values have therefore been used to estimate the quantity of water used per well during hydraulic fracturing, whilst the most recent data from Gallegos et al. (2016) [17] was used to estimate the quantity of water used during refracturing. This is consistent with the data used by Broderick et al. (2011). [6] Cuadrilla's estimate of the rate of flow back has been applied to both hydraulic fracturing and refracturing. Similarly the estimation of the quantity of proppant and chemicals provided by Broderick et al. (2011) [6] and Schneider (2014) [19] , respectively, have been used for both hydraulic fracturing and refracturing. This data is summarised in Table 3 below.

The material quantities in Table 3 are subject to uncertainty and variability from one well pad to another. There is reasonable consistency in the figures used for these material quantities between different studies, but the application of data from other geological formations to UOG extraction in Scotland introduces additional uncertainty which cannot be quantified.

Table 3: Materials quantities per well used for this analysis

Phase Material Quantity
Exploration Cuttings removed 140 m 3 per well
Appraisal
Production Hydraulic fracturing Water in 19,425 m 3 per well, [17] close to the mid-range figure identified by Broderick et al. 6
Water out 20 - 40% of water in (3,890 - 7,770 m 3)
Proppant in 5% by volume (970 m 3)
Chemicals in <1% by volume (<194 m 3)
Refracturing Water in 4,500 m 3
Water out 20 - 40% (900 - 1,800 m 3)
Proppant in 5% by volume of water (225 m 3)
Chemicals in <1% by volume of water (<45 m 3)
Decommission and restoration   No data

4.1.2 Coal-bed methane

Data on the movements of materials and equipment to and from coal-bed methane developments are not published in the same detail as for hydraulic fracturing, however much of the same equipment is required. The majority of available data is from the US, which was assumed to be applicable to CBM resources in Scotland. A fundamental difference between CBM and extraction of other forms of UOG using hydraulic fracturing is that the extraction of coal-bed methane requires the removal of water from the coal seam, in order to release the methane from the formation. The quantity of water removed is often substantial, with some estimates putting it at approximately 17,000 gallons (approximately 64 cubic metres) per well each day [20] .

Typically, this water is then removed from site using tankers to be disposed of via a number of routes ( e.g. evaporation/infiltration ponds, re-injection into deeper aquifers etc.). The rate of water extracted varies throughout the life of the well, with quantities peaking during the early stages of production and gradually falling in each subsequent year, for example wells in the Warrior Basin, located in the US States of Alabama and Mississippi, have been found to show falls in water production of between 70 and 90% after the first 1 to 2 months [21] . Overall, water production at coal-bed methane wells can be expected to peak within the first year, and decline throughout the remaining lifespan (~20 years).

4.1.3 Case study evidence

A Case Study was investigated to identify the material quantities associated with exploratory drilling and hydraulic fracturing carried out in 2011 at a single well located at Preese Hall, Weeton, Lancashire (see Appendix 1). The operator, Cuadrilla, reported the following total material quantities used for fracturing of this well:

  • Water: 8,399 m 3
  • Sand: 463 tonnes
  • Friction reducer: 3.7 m 3
  • Chemical tracer: 0.004 tonnes

The water quantity reported for this well has been used in the material quantity estimates developed by Broderick et al. This seems likely to constitute a relatively low total water requirement, as hydraulic fracturing was carried out for six stages only, of which one was presumably not fully carried out. The ratio of 5% proppant (sand) as a proportion of water used is reasonable in the light of data for Preese Hall.

The North Dakota rural UOG development case study includes an estimate of 2,300 vehicle movements associated with the development of an individual shale gas well. This was included in the analysis set out in the following section.

4.2 Traffic associated with onshore oil and gas activity

The movement of vehicles to and from onshore oil and gas sites is influenced by several factors, including the location and size of the facility, the nature of the underlying geology, and the availability of a local water source. Furthermore, the rate of vehicle movements fluctuates throughout the life of each well, with the intensity of vehicle numbers increasing during certain phases.

Several studies have been undertaken into the scale of vehicle movements associated with sites in both the USA and the UK, in light of the potential impact of these movements on the health and wellbeing of local communities.

The following table provides a summary of the estimated vehicle numbers occurring during the different development phases. For reference, the numbers of well pads and wells assumed in the economic scenarios are as follows:

  • Central scenario 20 well pads 15 wells per pad
  • High scenario 31 well pads 30 wells per pad
  • Low scenario 10 well pads 10 wells per pad
  • CBM scenario 2 well pads 15 wells per pad

Table 4: Estimated vehicle numbers at onshore oil and gas sites

Phase Activity Vehicle movements per pad Vehicle movements per well
Exploration & appraisal Well pad and road construction 4,315 - 6,590
(Six well pad drilled vertically to 2,000m and laterally to 1,200m)
2,856 - 7,890
(Heavy truck movements for a single 10-well pad of 10 laterals, over a 20 year lifespan)
10 - 45
(During the lifetime of a 6 well pad)
40 719 - 1,098
(Six well pad drilled vertically to 2,000m and laterally to 1,200m)
1,500
(Heavy truck movements during construction and development of a single gas well in the Marcellus shale region)
2,300
(Total drilling related truck trips per well at the Bakken formation in North Dakota)
2,000
(Per well drilled in the Marcellus Shale region, including transport of drilling rigs, workers, fracking fluids, water and removal of waste-water)
    558
(One way trips to a single well in Eagle Ford Shale - construction and drilling)
137
(One way trips to single well in Barnett Shale - drilling)
  3,950 heavy truck trips / 2,840 light truck trips (Estimated truck volumes for horizontal wells) 1,184 for initial production / <353 to maintain annual production (Loaded trucks per gas well)
Drilling rig 30 50
(Drill rig setup and well pad completion)
65
Drill fluid and materials 150 - 300 25 - 50 50 50
Drilling equipment (casing, drill pipe etc.) 150 - 300 25 - 50   10 (Casing)
Rig completion 15    
Completion fluid and materials 60 - 120 10 - 20 20 (Cement)
Completion equipment (pipes, wellhead, etc.) 30 5 45 (Pipe and other) 50 (Pipe)
Hydraulic fracture equipment (pumps, tanks etc.) 150 - 200     115 2750 (One way trips to a single well in Eagle Ford Shale - fracturing and production) 1350
(One way trips to a single well in Barnett Shale - fracturing and production)
 
Movement of workers to and from the site      
Production Drilling 75
(Cuttings and waste-water)
Proppant 120 - 150 20 - 25 180  
Fracturing fluid 2,400 - 3,600   400 - 600 450 455
Hydraulic fracturing        
Natural gas production
Refracturing 2,010 - 2,975             997
Natural gas production
Removal of waste-water   1,200 - 1,800 200 - 300 225 136    
Decommission and restoration              
Reference Broderick et al., 2011 [6] IoD, 2013 [4] Broderick et al., 2011 [6] IoD, 2013 [4] Broderick et al., 2011 [6] NYS DEP, 2009 [7] Tolliver, 2014 [9] Muehlenbachs and Krupnick, 2013 [22] Broderick et al., 2011 [6] Tolliver, 2014 [9] Li & Mikhail, 2014 [23] Li & Mikhail, 2014 [23] IoD, 2013 [4] NYS DEC, 2011 [7] TDT, 2012 [24]

As illustrated above, the number of vehicle movements occurring during the different stages of development varies significantly depending on the source, with estimations of heavy truck movements for single wells between well pad and road construction, and natural gas production, ranging from 719 to 3,950.

Several of the vehicle numbers provided in Table 4 have been derived from research undertaken by the New York State Department of Environmental Conservation, which has provided estimated numbers of one-way (loaded) trips per horizontal well. The NYSDEC published these estimations in a series of Draft Supplemental Generic Environmental Impact Statements (in 2009 and 2011), with the final SGEIS released in 2015. The estimated movements provided in this report are as follows:

Table 5: Estimated number of one-way (loaded) trips per well: horizontal well (Source: NYSDEC, 2015)

Well pad Activity Early Well pad Development (all water transported by truck) Peak Well pad Development (pipelines may be used for water transport)
Heavy truck Light truck Heavy truck Light truck
Well pad construction 45 90 45 90
Rig mobilisation 95 140 95 140
Drilling fluids 45 45
Non-rig drilling equipment 45 45
Drilling (rig crew, etc.) 50 140 50 140
Completion chemicals 20 326 20 326
Completion equipment 5 5
Hydraulic fracturing equipment (trucks and tanks) 175 175
Hydraulic fracturing water hauling 500 60
Hydraulic fracturing sand 23 23
Produced water disposal 100 17
Final pad prep 45 50 45 50
Miscellaneous - 85 - 85
Total One-Way, Loaded Trips Per Well 1148 831 625 795

Note: "Light" vehicles are defined in the NYSDEC study as comprising motorcycles and all two-axle, four-tyre vehicles. "Heavy" vehicles are defined as comprising all other vehicles

The NYSDEC estimation of traffic movements forms the basis of the traffic scenarios in this report, as discussed in Section 4.3.

4.3 Traffic scenarios

4.3.1 Individual site

As illustrated in Section 4.1, estimations of the quantity of materials and the number of vehicles required per well vary depending on the source, and are likely to be affected by a number of variables, such as the size of the well, the nature of the local geology and the technology in use.

This study has based its estimations of traffic movements on data provided by the New York State Department of Environment and Conservation ( NYSDEC). This approach was adopted because many other published analyses of traffic movements and impacts rely on the NYSDEC study. The NYSDEC report comprises the most reliable and comprehensive analysis of traffic movements associated with UOG activities. This has been supplemented with other data relevant to water quantities and coal-bed methane production. In addition, a number assumptions have also been made in order to provide projected traffic movements over the lifespans of the wells. Reliance on a single core study in this way could potentially introduce uncertainty into the analysis of traffic movements. However, the NYSDEC analysis is based on a wide range of industry sources. Where data can be cross-checked, the NYSDEC dataset is consistent with independent datasets. A more significant source of uncertainty is the application of data from the US to different shale gas formations in Scotland. This introduces an additional and non-quantifiable uncertainty into the traffic movements developed as part of this study.

The lifespan of each hydraulic fracturing site has been split into the following phases: 'Exploration and Appraisal', 'Production - Hydraulic Fracturing', 'Production - Refracturing' and 'Decommissioning', with the lifespan of coalbed methane sites split into 'Exploration', 'Production and 'Decommissioning'. The assumptions made for the activities within each phase in order to calculate vehicle movements for hydraulic fracturing and coal-bed methane are provided in Table 6 and Table 7, respectively. In these tables, for consistency with the New York State DEC study, "Light" vehicles includes motorcycles and all two-axle, four-tyre vehicles - that is, light trucks as well as cars. This contrasts with the UK definition of heavy goods vehicles, which comprises all vehicles with an unladen weight greater than 3500 kg. Hence, some vehicles in the "light" category in the tables below would be classified as " HGVs" in Scotland.

Table 6: Vehicle movement calculations at hydraulic fracturing sites, with and without water transport (Central scenario)

Phase Activity Water transport Vehicle type Description
Exploration & appraisal Well pad construction With & Without Heavy 45 one-way vehicle movements per pad [25] , spread over 4 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic for multi-well pad (2.4 to 3.6 hectares). Rounded up to 34 vehicle movements per week, over a 4-week period.
Light 90 one-way vehicle movements per pad [25] , spread over 4 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded up to 68 vehicle movements per week, over a 4-week period.
Rig mobilisation - assuming 1 vertical rig and 1 directional rig With & Without Heavy 95 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements. Rounded up to 24 vehicle movements per week, over an 8-week period.
Light 140 one-way vehicle movements per pad, for rig mobilisation, drilling fluids and non-rig drilling equipment [25] , spread over 8 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded up to 53 vehicle movements per week, over an 8-week period.
Drilling fluids With & Without Heavy 45 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 15 to reflect the quantity required for a 15 well pad. Rounded up to 169 vehicle movements per week, over an 8-week period.
Light See Rig mobilisation.
Non-rig drilling equipment With & Without Heavy 45 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded up to 17 vehicle movements per week, over an 8-week period.
Light See Rig mobilisation.
Drilling (rig crew etc.) With & Without Heavy 50 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded up to 19 vehicle movements per week, over an 8-week period.
Light 140 one-way vehicle movements per pad, for rig mobilisation, drilling fluids and non-rig drilling equipment [25] , spread over 8 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded up to 53 vehicle movements per week, over an 8-week period.
Completion chemicals With & Without Heavy 20 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 15 to reflect the quantity required for a 15 well pad. Rounded up to 75 vehicle movements per week, over an 8-week period.
Light 326 one-way vehicle movements, for completion chemicals, completion equipment, hydraulic fracturing equipment (trucks and tanks), hydraulic fracturing water hauling (incl. chemicals), hydraulic fracturing sand and produced water disposal [25] , spread over 16 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements to give 41 vehicle movements per week. Figure doubled following first fracturing phase to account for water disposal, totalling 82 vehicle movements per week during fracturing and waste disposal.
Completion equipment With & Without Heavy 5 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 15 to reflect the quantity required for a 15 well pad. Rounded up to 19 vehicle movements per week, over an 8-week period.
Light See Completion chemicals.
Hydraulic fracturing and Production Hydraulic fracturing equipment (trucks and tanks) With & Without Heavy 175 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Rounded up to 22 one-way vehicle movements per week, over an 8-week period. These movements are then repeated following the completion of hydraulic fracturing.
Light See Completion chemicals.
Hydraulic fracturing water hauling (incl. chemicals) Without only Heavy Water quantity required for a single well assumed to be 8,400 m 3, [6] divided by the assumed capacity of a single haulage vehicle (28 m 3), multiplied by 2 to reflect total vehicle movements, spread over an 8-week period [26] - 75 vehicle movements per week. Movements repeated for every well fractured.
With & Without Light See Completion chemicals.
Hydraulic fracturing sand With & Without Heavy Proppant (sand) quantity based on assumed value of 5% by volume of water, [6] which equates to 420 m 3, divided by the assumed capacity of a single haulage vehicle (28 m 3), multiplied by 2 to reflect total vehicle movements, spread over an 8-week period [26] - 4 vehicle movements per week. Movements repeated for every well fractured.
Light See Completion chemicals.
Flowback water removal With & Without Heavy Vehicles required to remove flow-back assumed to be 40% of total fracturing fluid [28] , equating to 120 one-way vehicle movements, spread over 8 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements. Rounded to 30 vehicle movements per week. Assumed to take place following the initial 8 week fracturing period and repeated for each subsequent fracturing period.
Light See Completion chemicals.
Production With & Without Heavy 3 one-way vehicle movements per well for the removal of water during gas collection [4] . Movements multiplied by 2 to reflect total vehicle movements and spread over a six-week period, eighteen weeks after the initial fracturing of each well - 1 vehicle movement per week for six weeks per well. The same frequency of vehicle numbers is assumed to repeat during re-fracturing.
Light 10 vehicle movements per wellpad per week were assumed following fracturing, to account for maintenance and on-going production, which remains constant until refracturing / decommissioning.
Refracturing and Production Hydraulic fracturing equipment (trucks and tanks) With & Without Heavy 175 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Rounded up to 22 one-way vehicle movements per week, over an 8-week period. These movements are then repeated following the completion of hydraulic fracturing.
Light 211 one-way vehicle movements, for hydraulic fracturing equipment (trucks and tanks), hydraulic fracturing water hauling (incl. chemicals), hydraulic fracturing sand and produced water disposal [25] , spread over 16 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements to give 26 vehicle movements per week. Figure doubled following first fracturing phase to reflect water disposal, totalling 53 vehicle movements per week during fracturing and waste disposal.
Hydraulic fracturing water hauling (incl. chemicals) Without only Heavy Water quantity required for the refracturing of a single well assumed to be 4,500 m 3 (Low estimate) [6] , divided by the assumed capacity of a single haulage vehicle (28 m 3), multiplied by 2 to reflect total vehicle movements, spread over an 8-week period [26] - 40 vehicle movements per week. Movements repeated for every well fractured.
With & Without Light See Hydraulic fracturing equipment.
Hydraulic fracturing sand With & Without Heavy Proppant (sand) quantity based on assumed value of 5% by volume of water, [6] which equates to 225 m 3, divided by the assumed capacity of a single haulage vehicle (28 m 3), multiplied by 2 to reflect total vehicle movements, spread over an 8-week period [26] - 2 vehicle movements per week. Movements repeated for every well fractured.
Light See Hydraulic fracturing equipment.
Flow back With & Without Heavy The number of vehicles required to remove flow-back assumed to be 40% of total fracturing fluid [28] , equating to 64 one-way vehicle movements, spread over 8 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements. Rounded to 16 vehicle movements per week. Assumed to take place following the initial 8 week fracturing period and repeated for each subsequent fracturing period.
Light See Hydraulic fracturing equipment.
Production With & Without Heavy See Hydraulic fracturing and Production - Production.
Light 10 vehicle movements per wellpad per week were assumed following fracturing, to account for maintenance and on-going production, which remains constant until decommissioning.
Decommission   With & Without Heavy 45 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Vehicle movements multiplied by 2 to reflect total vehicle movements. Rounded to 11 vehicle movements per week over an 8-week period.
Light 50 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Vehicle movements multiplied by 2 to reflect total vehicle movements. Rounded to 13 vehicle movements per week over an 8-week period.

Table 7: Vehicle movement calculations at coal-bed methane sites (Central scenario)

Phase Activity Vehicle type Description
Exploration and appraisal Well pad construction Heavy 45 one-way vehicle movements per pad [25] , spread over 4 weeks. [26] Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded up to 34 vehicle movements per week, over a 4-week period.
Light 90 one-way vehicle movements per pad [25] , spread over 4 weeks [26] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded up to 68 vehicle movements per week, over a 4-week period.
Drilling rigs Heavy 2 one-way vehicle movements per pad [29] , spread over 2 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded to 2 vehicle movements per week, over a 2-week period.
Drilling pipe vehicles Heavy 4 one-way vehicle movements per well [29] , spread over 6 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 15 to reflect the quantity required for a 15 well pad. Rounded up to 20 vehicle movements per week, over a 6-week period.
Casing vehicles Heavy 5 one-way vehicle movements per well [29] , spread over 6 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 15 to reflect the quantity required for a 15 well pad. Rounded up to 20 vehicle movements per week, over a 6-week period.
Tank vehicles and other equipment Heavy 5 one-way vehicle movements per pad [29] , spread over 6 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded to 3 vehicle movements per week, over a 6-week period.
Survey equipment vehicles Heavy 2 one-way vehicle movements per pad [29] , spread over 6 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded to 1 vehicle movements per week, over a 6-week period.
Cabin vehicles Heavy 5 one-way vehicle movements per pad [29] , spread over 6 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [26] to reflect increase in traffic to multi-well pad. Rounded to 3 vehicle movements per week, over a 6-week period.
Water tankers for used water Heavy 7 one-way vehicle movements per well [29] , spread over 6 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 15 to reflect the quantity required for a 15 well pad. Rounded up to 35 vehicle movements per week, over a 6-week period.
Steel lining vehicles Heavy 2 one-way vehicle movements per well [29] , spread over 6 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 15 to reflect the quantity required for a 15 well pad. Rounded up to 10 vehicle movements per week, over a 6-week period.
Foul sewage tanker Heavy 1 one-way vehicle movements per well [29] , spread over 6 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 15 to reflect the quantity required for a 15 well pad. Rounded up to 5 vehicle movements per week, over a 6-week period.
Tankers to remove excess drilling fluids Heavy 3 one-way vehicle movements per well [29] , spread over 6 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 15 to reflect the quantity required for a 15 well pad. Rounded up to 9 vehicle movements per week, over a 6-week period.
Skips Heavy 4 one-way vehicle movements per pad [29] , spread over 6 weeks (assumed timeframe). Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded to 12 vehicle movements per week, over a 6-week period.
Drilling supplies (transit size) Light 3 one-way vehicle movements per well [29] per week. Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded up to 9 vehicle movements per week, over a 6-week period.
Personnel vehicles (cars or vans) Light 42 one-way vehicle movements per well per week [29] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded up to 126 vehicle movements per week, over a 6-week period.
Production Produced water disposal Heavy Coalbed methane wells are estimated to require the removal of approximately 17,000 US gallons of water per day [30] , at their peak, which equates to 64 cubic metres. When divided by the capacity of a single haulage vehicle (28 m 3), this equates to 16 one-way vehicle movements per week. This number has been multiplied by 2 to reflect total vehicle movements, to give 32 vehicle movements per week per well, which continues for a 4-week period. Following the initial 4-week period, the quantity of water removed from the initial well is assumed to fall by 80%, [21] with production at a second well occurring simultaneously, resulting in 38 vehicle movements per week, over a 4-week period. This increase in movements continues as each well is brought into production, resulting in a peak in vehicle movements of 122 per week, during water removal from the 15 th well. Once all wells are in production it is assumed that water extraction reduces by 1 percentage point per year
Personnel vehicles (cars or vans) Light 42 one-way vehicle movements per well per week [29] . Vehicle numbers multiplied by 2 to reflect total vehicle movements and by 1.5 [27] to reflect increase in traffic to multi-well pad. Rounded up to 126 vehicle movements per week, over a 6-week period. Use of personnel vehicles assumed to be continuous during each well development stage. Once all wells are established it has been assumed the rate of vehicle movements falls in line with the rate of water extraction ( i.e. a reduction of 1 percentage point per year).
Decommissioning Final pad prep Heavy 45 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Vehicle movements multiplied by 2 to reflect total vehicle movements. Rounded to 11 vehicle movements per week over an 8-week period.
Light 50 one-way vehicle movements per pad [25] , spread over 8 weeks [26] . Vehicle movements multiplied by 2 to reflect total vehicle movements. Rounded to 11 vehicle movements per week over an 8-week period.

This data has been used to provide an estimation of vehicle movements (moving to and from site) for a single hydraulic fracturing site and a single coal-bed methane site, under the following scenarios:

1. Hydraulic fracturing site (single pad), based on the Central, High and Low economic scenarios, including refracturing 10 years after the initial fracturing, decommissioning 20 years after construction, and the use of a dedicated pipeline delivering water to the site.

2. Hydraulic fracturing site (single pad), based on the Central, High and Low economic scenarios, excluding refracturing, with decommissioning 20 years after construction, including the use of a dedicated pipeline delivering water to the site.

3. Hydraulic fracturing site (single pad), based on the Central, High and Low economic scenarios, including refracturing 10 years after the initial fracturing, decommissioning 20 years after construction, with water delivered to the site by tanker.

4. Hydraulic fracturing site (single pad), based on the Central, High and Low economic scenarios, excluding refracturing, with decommissioning 20 years after construction, with water delivered to the site by tanker.

5. Coal-bed methane site (single pad), based on the Central economic scenario of 15 wells, excluding hydraulic fracturing, with water removed by tanker and decommissioning occurring 10 years after the establishment of each well.

The estimated traffic numbers under these Scenarios are provided below.

Table 8: Estimated total traffic movements per well pad over well pad lifetime

Scenario Vehicle type No re-fracturing, no water transport With re-fracturing, no water transport No re-fracturing, with water transport With re-fracturing, with water transport Coal-bed methane
    Total over 20 year
period approximately
Total over 12 year period approximately
Central Light 11300 20400 14800 23800 48,800
Heavy 7300 9900 16300 23700 44,300
High Light 21500 39500 28400 46400  
Heavy 13700 18900 31900 46700  
Low Light 8000 14000 10300 16300  
Heavy 5100 6900 11100 16000  

Note: "Light" vehicles includes motorcycles and all two-axle, four-tyre vehicles - that is, light trucks as well as cars. The "Light" vehicle numbers include some vehicles which would be classified as HGVs in Scotland.

The following graphs illustrate the estimated vehicle movements for each of these examples, under the Central scenario.

Figure 5: Estimated traffic movements at a 15 well pad, with refracturing, with water transport

Figure 5: Estimated traffic movements at a 15 well pad, with refracturing, with water transport

Figure 6: Estimated traffic movements at a 15 well pad, without refracturing, with water transport

Figure 6: Estimated traffic movements at a 15 well pad, without refracturing, with water transport

Figure 7: Estimated traffic movements at a 15 well pad, with refracturing, without water transport

Figure 7: Estimated traffic movements at a 15 well pad, with refracturing, without water transport

Figure 8: Estimated traffic movements at a 15 well pad, without refracturing, without water transport

Figure 8: Estimated traffic movements at a 15 well pad, without refracturing, without water transport

Figure 9: Estimated traffic movements at a CBM well pad

Figure 9: Estimated traffic movements at a <acronym>CBM</acronym> well pad

Development could potentially take place in a more intensive way at individual well pads - for example, one well pad might have more than one drilling rig operational at one time, or might carry out drilling at the same time as hydraulic fracturing. If this were to take place, the associated traffic impacts would be higher than those presented above, but for a shorter duration.

4.3.2 National scale assessment

Estimations of the national impacts of hydraulic fracturing facilities have also been developed. The average numbers of vehicle movements forecast for the range of scenarios considered in this study across Scotland are summarised in Table 9. These movements can be expected to take place mainly in the areas shown in Figure 1 and Figure 2.

Table 9: Forecast average weekly vehicle movements across Scotland

Economic scenario Well pad scenario Average light vehicle movements per week Average heavy vehicle movements per week
Central

20 well pads

15 wells per pad
No water transport, no refracturing 257 164
No water transport, with refracturing 461 223
With water transport, no refracturing 335 369
With water transport, with refracturing 539 537
High

31 well pads

30 wells per pad
No water transport, no refracturing 398 254
No water transport, with refracturing 714 346
With water transport, no refracturing 519 571
With water transport, with refracturing 835 832
Low

10 well pads

10 wells per pad
No water transport, no refracturing 128 82
No water transport, with refracturing 230 112
With water transport, no refracturing 167 184
With water transport, with refracturing 269 268
CBM

2 well pads

15 wells per pad
No decline, no fracturing 52 47

This indicates that UOG development could result in 210 to 1667 traffic movements per week on average, mainly within the central belt of Scotland. CBM development could result in an estimated additional 99 traffic movements per week. For context, approximately 4.3 million trips were made by cars and goods vehicles in Scotland each weekday in 2012. [31]

The forecast pattern of weekly average traffic movements over the period 2023 to 2055 is shown in Figure 10 for the Central scenario.

Figure 10: Regional estimation of vehicle movements under the Central scenario, including hydraulic fracturing and coal-bed methane

Figure 10: Regional estimation of vehicle movements under the Central scenario, including hydraulic fracturing and coal-bed methane

The incremental traffic movements due to UOG activity would have no detectable effect on the overall numbers of traffic movements in Scotland. Hence, there would be no detectable impact on associated environmental issues such as national carbon dioxide emissions from road traffic.

This indicates that the key area of concern in relation to potential traffic impacts is the potential for local effects associated with vehicle movements to/from specific sites.

4.3.3 Traffic movements for associated activities

A number of activities associated with UOG development could also generate traffic. Such activities could include the following:

  • Gathering and laying mains pipelines
  • Constructing Compressor stations
  • Gas processing and cryogenic plant for production of LNG
  • Creating and utilising a water treatment infrastructure
  • Building or extending road connections to gas well pads and other facilities.

The need for these associated activities would vary greatly depending on a number of factors such as location, the need to construct a facility to serve a high number of wells or the need to construct a pipeline or an access road. The traffic associated with such activities would also vary greatly as a result of many factors such as the length of road to be constructed, the length and diameter of water main to be provided, number of pipes and the size of wastewater treatment works to be constructed.

It may sometimes be possible to include some of the associated activities within the planning application for the well pads such as the construction of a new access road or a compressor station. In these circumstances, these activities would be included in the construction programme and vehicle generation numbers would be stated in the EIA. In other cases, such as the construction of a regional wastewater treatment plant, it is likely that a separate planning application would be submitted, which would identify vehicle generation numbers. Either way, EIAs for UOG development should consider cumulative impacts with other traffic generating development, including (but not limited to) other UOG activity. In any case, the combined traffic impacts of multiple well pad developments and associated infrastructure should be taken into account via the Strategic Environmental Assessment process for strategic and local development plans.

Mains water pipelines do not normally require planning consent as the infrastructure would generally be delivered by Scottish Water as a statutory undertaker. A pipeline would require Scottish Water Approval and an EIA may be required as a Schedule 2 development, if the total area of works exceed 1 hectare, having regard to the characteristics and location of the pipeline, and the potential impacts. In terms of traffic movements associated with the laying of a water main, there would be a limited number of heavy goods vehicles associated with the delivery of pipe and machinery to excavate and lay the pipe. However, the vehicle numbers associated with the laying of new water pipework would be negligible when compared with the vehicle numbers associated with the production stage of the well pads.

If new road connections are required, a detailed assessment of traffic and other potential impacts should be included within the EIA. The length of new road should be calculated along with the quantities of materials required to construct the road. This would then allow the associated vehicle movements to be calculated, the impacts assessed and managed, and a programme established for the delivery of materials.

The Letham Moss case study provides an indication of vehicle movements associated with the construction of a Gas Delivery and Water Treatment Facility ( GDWTF) for coal bed methane development. It was anticipated that there would be a maximum of 30 two-way vehicle movements ( HGV/ LGV) per day during the construction phase while during operation there would be approximately 6 vehicles per day accessing the site. Construction phase traffic movements for the GDWTF were approximately 20% of the highest predicted numbers of vehicle movements. For more widespread shale gas development, it would be expected that construction of a water treatment plant would serve a number of well pads, and would represent a smaller proportion of vehicle movements.


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