Les chercheurs au Tyndall Centre à l'université de Manchester, en Angleterre, ont enquêté sur les impacts du gaz de shale on the environment and climate change. The exploitation of shale gas, or shale, is launched in the U.S. and will begin soon in Britain. Here the 9th part of a loose translation of the preliminary report from the Tyndall Centre for Climate Change Research. The original is here:
http://www.tyndall.ac.uk/shalegasreport
with a link to download the report in pdf format of 87 pages.
The report's title is: 
4.2.3 Contamination of groundwater
The importance of groundwater pollution
Groundwater is water that accumulates in the rock formations and are called aquifers. The water fills the aquifer naturally from bottom to top, filling the spaces in the rock with water and creating the saturated zone of the aquifer to the bottom, and the non- saturated in the shallower parts where the pockets in the rock contain air and water. The boundary between the saturated zones and is non-saturated groundwater (water table). Groundwater is not stationary but flows through and along cracks where the water enters the aquifer (recharge area - reload zone) to a region where water leaves the aquifer (discharge zone). When this happens near the surface, a spring is fed and the flow of rivers and wetlands. The quality of groundwater is usually very good and requires little or no treatment before use as drinking water. In England and Wales, groundwater provides a third of drinking water supplies and the flow of several rivers. In some parts of southern England, groundwater provides up to 80% of needs water. Given the importance of groundwater as drinking water source and water source for rivers and wetlands, prevent pollution is vital. If there is contamination and pollution penetrates deeply, this could lead to a deterioration of the resource over the long term.
fluids fracturing and flowback (including processed products and contaminants mobilized underground) contain a number of hazardous substances which, if they contaminate groundwater, have significant impacts on the quality of drinking water and / or surface water and wetland habitats. The severity of damage depends example of the importance of the aquifer, the extent and nature of contamination, the concentration of hazardous substances and the link between surface water and groundwater.
roads
contamination routes of exposure most obvious contamination of groundwater by gas wells and shale are
- a catastrophic failure or loss of integrity of entire or partial hole drilling during construction, hydraulic fracturing, operation or after closing the well.
- migration (movement) of contaminants from the fracture of the geological target from underground including: +
outside the borehole itself
+ other boreholes (wells as incomplete, poorly constructed or other older drill holes or poorly sealed) +
caused by fractures during the process of hydraulic fracturing or
+ by natural fissures, cracks and interconnected spaces.
failures or loss of integrity of borehole
Because of the great depths of the resource in the shale, boreholes will be drilled through probably more aquifers. Throughout the life of a well, the borehole is a link constant between the target formation (where hydraulic fracturing occurs at high pressures and the subsequent extractions are conducted), and other rock formations, saline aquifers, freshwater aquifers and the surface. Because of this, the borehole itself is probably the main route of contamination of groundwater.
To reduce the possibility of contamination of the well itself, the forms are installed to isolate the drill hole of the surrounding formations. It should be noted that the requirements under the depths vary from state to state as well as requirements for cementing casings. As already mentioned in Section 2.2, the method of "traffic" can be used to completely fill the space between the casing and the borehole (annulus) from the bottom of surface casing to the surface. However, according to GWPC,
- Traffic on the cement surface casing is not a universal obligation and in some states, the cementation of space around the annulus is required only if the casing through the zone Groundwater deepest but not all areas of groundwater
- although some states require a complete movement of cement from the bottom to the head of formwork production, plupar States require that only an amount of cement calculated to raise the head cement behind the casing to a certain level above the producing formation;
- in deep wells (as is often the case wells drilled shale horizontally), the flow of cement is more difficult to achieve since the cement must be handled in several stages and may result in poor quality work or damage the concrete formwork if not done correctly.
is clear that once completed, the forms in the holes are the first line of defense against contamination of groundwater. As such, the loss or the initial lack of integrity of all forms of the well anywhere along the borehole have the potential to be the source of contamination of geological formations including aquifers.
The catastrophic failure of a well casing (eg during hydraulic fracturing, high pressure), provided that the partial loss of integrity of sealed concrete facts wrong could result in a pollution incident. The severity of such events depend on the nature of the loss of integrity, contaminants and the environment that suffers. For this events is due to the loss of integrity of the formwork, contamination resulting from flowback of fracturing fluid through the casing itself could occur but would require a physical failure of steel formwork and cement. It would be more likely that reflux up through the annulus between the casing and cemented the training would be by GWPC, would represent the biggest danger of contamination of ground water during hydraulic fracturing, "is the cementing of the casing that added the greatest value for groundwater protection ... in effect, the quality of the initial work of cementing is the most important factor to prevent the movement of fluids from the deeper areas to ground water resources. "
Document New York State (2009) does not take any account of the role and importance of cementing and in particular the work initial cementation when he leans on pollution of groundwater. It is virtually aside the issue by referring to a study funded by ICF International, which was based on an estimate of risk in a study of the 1980s made by the American Petroleum Institute (API). The study analyzed the API the risk of contamination of wells Class II built correctly for Underground Source of Drinking Water (USDW) - underground source of drinking water - caused by corrosion of casing and cement seal failure. Based on this, the study of the ICF (and New York State, 2009) concluded that the likelihood of fracturing fluids can go to a USDW because of flaws in the formwork or concrete is estimated at less than 2 X 10-8 (less than 1 chance in 50 million wells). Based on this, the study of ICF concluded that hydraulic fracturing does not pose a potential risk due to negative environmental impacts of potential aquifers for freshwater. Looking
this better, one might think that the forecast and the conclusion could be problematic in several respects. The most remarkable is that the rigorous analysis of risk requires that we include all the circumstances reasonably likely, events and places of failures that may cause adverse impacts. As such, focusing only on the estimated risk of failure in properly constructed wells do not take into account the risks of failure of poorly constructed wells. Although imperfect construction of a well could be involuntary, it happens in reality and it has resulted in pollution events (see later in the report). Since the study risk requires consideration of unintended consequences is a serious omission, especially since we know that construction defects are recognized as the most significant risk to groundwater.
Another issue to consider is the comparison between the injection wells and gas wells hydraulically fractured shale. Although the study of ICF reflects the difference between the two, it assumes that the risks from shale wells are probably lower because the injection well is with sustained pressure, while gas wells hydraulically fractured shale under pressure only during hydraulic fracturing (After which the pressure in the forms is less than in the surrounding formation). Although operational differences are real, at pressures of 5,000 to 10,000 psi (345 to 690bar) pressure from the hydraulic fracturing are higher and are applied several times during the fracturing of a well. This means that the well and the casing are subjected to repeated episodes of high pressure followed by complete release of pressure and negative pressure relative to surrounding rock. So, one could assume that much stress on the well casings and sealed cement "inflations and deflations" repeated could be greater and the damage and subsequent loss of integrity of the formwork may occur more in gas wells hydraulically fractured shale.
Considering all this, it seems problematic to conclude that there is no reasonable potential risk for freshwater aquifers. especially given the likelihood of contamination of aquifers by wells. While thousands of gas wells are drilled through shale aquifers in the United States, the figure presented as a probability of contamination USDW should be presented as a factor of one thousand times higher than the one provided. For cons, the document New York State (2009) states that the migration of natural gas is a reasonable concern over early when it is potentially significant adverse impacts due to:
- inadequate depth or the integrity of the surface casing to isolate the sources of fresh drinking water deeper formations containing gas;
- inadequate cement in the annulus around the surface casing which could be due to gas flow or because the period not long enough to allow the cement to "take";
- of the excessive pressure in the annulus between the casing and surface forms intermediate and production. Such pressure could break training at the base of the formwork surface and would result in the creation of underpasses outside the surface casing. Excessive pressure could occur if the gas seeps in the annulus due to a lack of cement around the production casing and the annulus is not vented to the specifications of forms and cementation. So, firstly, the evaluation of hydraulic fracturing of the document New York State (2009) ignores the possibility of contamination due to faulty construction but cons, the possibility of such a construction defect is qualified as a reasonably anticipated more anxiety (a more Reasonably Anticipated concerned).
This oversight is remarkable for the fact that there are a number of documented examples of pollution events caused by faulty construction and operator errors. There are reports that describe incidents of contamination of surface and groundwater by contaminants such as brines, of unidentified chemicals, with natural gas, sulfates and hydrocarbons such as benzene and toluene. In several cases, the exact cause or pathway of contamination are still not identified because of the difficulty to map the complex formations of the basement, but there are also several incidents where cases such as construction defects have been identified. Those include:
1) In 2004, in Garfield County, Colorado, we saw natural gas bubble in a creek bed. In addition to natural gas, groundwater samples contained concentrations of benzene greater than 200 micrograms per liter concentrations in surface water exceeded 90 micrograms per liter (90 times more than the limit tolerated by the state). The operator failed to follow instructions to avoid potential problems during drilling, failed to notify authorities as required by its permit drilling and did not properly sealed with cement the well casing. This, in conjuncture with the existence of a network of fractures and faults have been the source of significant quantities of formation fluids that have migrated nearly 4,000 feet (1,200 meters) horizontally and 2,000 feet (600 meters) to eventually seep to the surface. Although forms of remediation wells installed in the reduced seepage in a report, the ensuing plume of benzene requires patches since 2004. Followed hydrological studies that have determined that concentrations of methane and other contaminants in the ambient groundwater in the region have increased during the increase in drilling activity, and attributed the increase or inadequate forms of bonding in gas wells and the fractures Natural.
2) In 2007, a well was drilled to a depth of almost 4,000 feet in a formation of sand packed (tight sand formation) in Bainbridge, Ohio, had not been properly sealed with cement, leaving gas escape from a layer of shale above the sand formation. The gas escaped through the annulus to enter a groundwater source of drinking water. Methane accumulated until an explosion in the basement of a residence alert the authorities of the state.
3) Contamination of groundwater due to drilling in the Marcellus shale formation was reported in 2009 in Dimock, Pa., where methane has migrated thousands of feet of production training, contaminating freshwater aquifer and resulting in at least one explosion on the surface. Methane migration has been reported to have impacted at least a dozen drinking wells in a region with an area of 9000 square (23 square kilometers). The explosion occurred due to the accumulation of methane in a vault of drinking water wells. The Pennsylvania Department of Environmental Protection (DEP) has installed gas detectors and has disconnected the water wells that had high levels of methane that could cause explosions in homes that were connected. The primary cause is still under investigation and an underpass is still not definitively known.
4) In July 2009, McNett County, Pennsylvania DEP has discovered a natural gas leak associated with a well drilled. Both rivers have been affected by the leakage of methane has also impacted several private drinking water wells in the region and one resident was forced to evacuate. A report by the Pennsylvania DEP subsequently identified the suspected cause of the leak as any failure of the formwork. The investigation continues.
5) In April 2009, in Foster County, Pennsylvania, drilling activities have impacted at least 7 sources of drinking water. Gas leaks were evident in several wells and residents have complained. Two sources of drinking water contained methane and 5 of them were of iron and manganese at concentrations above the allowable limits for drinking water. After investigation, the DEP ruled that the state of the gas leak was the result of recently drilled 26 wells, 4 of them had excessive pressure on the formwork surface, and others did not return cement (cement returns), according to Riverkeeper.
6) December 12, 2006, the Pennsylvania DEP sent a notice to two companies that had violated several times and continued to violate state law and had demonstrated a lack of ability or intent to comply with the requirements of environmental laws. Among the violations cited had been over-pressurized wells, which caused the migration of gas and contaminated groundwater had not implemented controls erosion and sedimentation on the well sites, which accelerated erosion ; had spilled brines without permit on the ground and they had encroached into waterways without a permit.
7) in Fremont County, Wyoming, responding to complaints of bad odors and the water tasted bad in residential wells, EPA region has financed a survey to find the source and nature of the contamination. The report took into account data collected from residential wells and municipal Pavilion, Wyoming, in March and during the month of May in 2009. The report determined that high levels of contaminants in several drinking water wells, some of the same chemicals used during a hydraulic fracturing operation close by.
8) June 3, 2010, a gas well had a "blowout" in Clearfield County, ejecting gas and sewage in the air for 16 hours. The blowout has gone up to 75 feet high, according to some media reports, before a team of emergency first responders from Texas to seal the wells. It blamed the blowout on the poorly trained staff and inadequate control procedures, and operators of the well received penalties of $ 400,000 and were ordered to cease drilling operations throughout the state for 40 days.
In addition to the evidence that contamination of groundwater through this transition can happen, and indeed happens, that voluntary action on the use of certain toxic substances in fracturing fluids were passed based on unnecessary risk implies that there is a risk of potential concern. The report GWPC that diesel has been mentioned as the main ingredient concern by the Oil and Gas Accountability Project (ogapi) because it contained relatively large amounts of benzene. An agreement was made to discontinue its use as a fracturing fluid in methane projects in coal formations CBM) in areas that are considered USDW. This action, therefore, is in conflict with the general conclusion that hydraulic fracturing does not pose a reasonable risk of potential significant adverse impacts to the freshwater aquifer potential.
The following free translation of the Tyndall Report will focus on the risks of contamination by land, water consumption, visual pollution and noise, and the conclusions of the report Tyndall in a blog entry soon.
Photo: Helen Slotte
0 comments:
Post a Comment