Seismic surveying stage
Seismic surveys are usually delivered using a set of heavy vibrator trucks that generate seismic waves (Vibroseis method). At this stage, air emission sources are:
- exhaust gas emitted by Vibroseis trucks during travel and operation. Key exhaust gas components are: carbon dioxide, nitrogen oxides, sulfur dioxide, hydrocarbon and dust,
- dust raised by Vibroseis trucks on field roads and in rainless periods.
Seismic teams travel twice a day (to the seismic line and back to seismic base).
The trucks move one after another along the seismic line. Emissions during the travel are low and may vary in time and from one location to another. The impact is comparable to that of vehicular traffic and operation of agricultural machines in the field.
Sometimes, seismic tests are delivered using explosives. Charges are detonated in shallow (up to several meter deep) special purpose wells. Explosive-based seismic surveys involve the following air emission sources:
- traffic of vehicles and operation of engine-powered machinery (e.g. truck-mounted rigs for shot hole drilling, water delivery trucks, recording systems, measuring equipment, etc.).
The explosion occurs under the ground (usually at a depth of 2 to 6 metres, exceptionally 10+ m). If properly delivered, explosion does not involve any emissions to the air.
Drilling stage
Drill site development
Normally, it takes 4 – 6 weeks to build the drill site.
At drill site development stage, chief air emission sources are:
- heavy equipment operation during construction and assembly works,
- traffic of vehicles that deliver the equipment, components and materials,
- operation of Diesel-powered generator sets,
- dust raised during earthwork, for example site leveling or the building of embankments around the site.
Impacts on the air are of a short duration at site development stage and will cease on completion of construction works.
Drilling stage
Well drilling is the next stage. Normally, it takes 3 to 8 weeks to drill a well. Drilling operations are delivered on a continuous basis, i.e. round-the-clock and seven days a week.
At the drilling stage, the main air emission sources are:
- operation of Diesel-powered generator sets,
- operation of mud treatment devices (shale shakers, hydrocyclones, centrifuges, desanders, etc.),
- fans,
- final process procedures at the drill site,
- traffic of vehicles that deliver the equipment, components and materials,
- on-site boiler for heating rooms and water.
Key emissions at this stage are: dusts, sulfur dioxide, nitrogen oxides and carbon oxide.
Reservoir stimulation stage
At reservoir stimulation stage, chief air emission sources are:
- operation of pump sets that inject pressurized fracturing fluid into the well. The number of installed pump sets will depend on the size of the well and job parameters (e.g. the required pressure. Several to more than ten pump sets may be operated simultaneously at the fracturing stage. The sets are Diesel powered. Each pump set is fitted with exhaust gas vent,
- traffic of vehicles that deliver the equipment, components and materials,
- other process procedures performed at the drill site (e.g. silo filling),
- gas flaring, in the event of gas (or oil with associated gas) production from the well,
- on-site boiler for heating rooms and water.
A single fracturing procedure is usually of a short duration (a few hours) and it takes a few or several days to complete the entire process (involving a few or several procedures). Breaks of a day or a few days (a few or several dozens of hours) may occur between individual procedures.
Key emissions at this stage are: dusts, sulfur dioxide, nitrogen oxides and carbon oxide.
Well testing and test production stage
Fracturing jobs are followed by tests that are intended to estimate productivity and production parameters of the well. Well testing duration may vary, but most often it takes 3 months to complete the tests. The purpose of the test production is to establish the rate of gas production and its decrease with time.
Test production under a concession for oil and gas exploration and appraisal may be conducted for a period of several months and up to two years (in accordance with Geological and Mining Law). Gas extracted at test production stage may be delivered to the local distribution network for commercial use.
Chief air emission sources at well testing and test production stage are:
- operation of Diesel-powered generator sets,
- traffic of vehicles that haul flowback water out of the drill site,
- well kicking operations (nitrogen gas pumping, etc.),
- gas flaring, in the event of gas (or oil with associated gas) production from the well,
- on-site boiler for heating rooms and water.
Natural gas is flared to avoid a release of gas components (methane in particular) to the atmosphere.
Chief emissions at the stage of well testing and test production are: dusts, sulfur dioxide, nitrogen oxides and carbon oxide.
Well abandonment and site reclamation stage
On completion of operations the rig will be removed and the site cleared and reclaimed.
Chief air emission sources at well abandonment and site reclamation stage are:
- heavy equipment at dismantling, demolition and rehabilitation operations,
- traffic of vehicles hauling out the equipment, materials and wastes,
- Diesel-powered generator sets,
- dust emissions from earthwork.
Protection of atmospheric air during exploration
Is it possible to minimize the emissions of air pollutants in shale gas exploration and if yes, then how?
In all shale gas exploration stages the following measures are applied to minimize or eliminate the emissions of air pollutants:
- use of equipment that ensure proper emission parameters, i.e. height and diameter,
- keeping the emission time as short as possible,
- use of top quality fuels to power combustion engines and generator sets,
- use of Diesel fuel (emitting much less pollutants than coal) in room and water heating,
- imposing speed limits for vehicles on unsurfaced, macadam and slag-surfaced roads so as to minimize dusting,
- application of efficient equipment in accordance with its intended use.
Did you know that...
- Dust and gas emissions to the air from shale gas exploration well drilling are comparable to those that occur at drilling conventional gas exploration wells. Time is the only difference, as it takes longer to drill a shale gas well with a horizontal leg and perform operations in the borehole, such as hydraulic fracturing.
author: Anita Starzycka
