Impact Of Hydraulic Fracturing Research Articles

Study on Fault Activation Evaluation Mechanism and Sensitivity Analysis in Shale Gas Hydraulic Fracturing

Shale gas hydraulic fracturing usually activates nearby faults and makes them slip. In horizontal wells, fault slip can result in serious casing deformation. Casing deformation slows the fracturing process, lowers production, and raises the cost of a shale gas well. It is challenging to obtain underground data on fault activation because of the deep shale reservoirs. As a result, the current study needed to indicate how hydraulic fracturing affects fault activation length. This made it challenging to control casing deformation. The fluid-structure coupled finite element method was used in this study to create a coupled seepage-stress model for heterogeneous shale formation. With microseismic signs and hydraulic fracking for shale gas, this model examined the variation law of pore pressure and ground stress. The fault activation coefficient was created to assess the fault activation duration and the impact of hydraulic fracturing. The model was verified by the microseismic signal. The outcomes of the numerical simulation demonstrate how the rapid rise in formation pore pressure during hydraulic fracturing affected the ground stress at the fault interface. The influence of ground stress variation at the fault interface on fault activation could not be ignored. Increased fault elastic modulus, fracture pressure, fracture time, and the fault Poisson ratio result in longer fault activation lengths. The length of the fault’s activation was decreased by the increase in fracture stage, distance from the fault, friction angle within the fault, and fault angle. Finally, a shale gas horizontal well with casing deformation in block C was analyzed. The results showed that reducing the fracturing duration can reduce the activation length of the fault by 68.25%, resulting in a 9.1 mm fault slide and a 0.86 mm casing deformation, respectively. This study offers theoretical guidelines for preventing fault activation during hydraulic fracturing in horizontal shale gas wells.

Impact of hydraulic fracturing on development indicators at BS10, BS11, US11 zones of Yuzhno-Yagunskoye field

The study considers three production zones of Yuzhno-Yagunskoye field. The study analyzes one method of oil intensification from the formation, namely Hydraulic Fracture Treatment (HFT), and provides the results of its influence on development indicators within three zones of Yuzhno-Yagunskoye field. A series of hydraulic fracturing operations was carried out in the period from 1995 to 2017. The methods for analyzing the bottomhole zone of the formation were used to process field data. However, it should be noted that in comparison with previous periods of hydraulic fracturing technology, the effect is reduced, which implies further modification of the used hydraulic fracturing technology. The purpose of this study is to evaluate the process efficiency of hydraulic fracturing at Yuzhno-Yagunskoye field. The above results were used during hydraulic fracturing at Yuzhno-Yagunskoye field.

Impact of hydraulic fracturing on the creation of highly permeable channels within the Earth’s interior

in modern times hydrocarbon production in fields with hard-to-recover reserves is actively being implemented. This trend is caused by the depletion of conventional reserves, which increases every year of operation. In Russia, most of the hard-to-recover reserves belong to deposits with low-permeability channels and deteriorated reservoir properties. The cost-effective utilization of such subsoil resources is only possible using special technologies that can increase well productivity. One of the most commonly used technologies is hydraulic fracturing (HFT). This study analyzed the impact of HFT on the creation of highly permeable channels as a stimulation method. The methodology for the selection of well candidates for HFT was identified, its effectiveness and practical significance were evaluated.

Study on the Impact of Hydraulic Fracturing on Surrounding Ancillary Buildings considering SSI

Hydraulic fracturing is a key technology in the development of unconventional oil and gas reservoirs. With the continuous industrialization and large-scale development of shale gas production in China, the workload of hydraulic fracturing is also increasing rapidly, and the induced seismic events are also increasing gradually, resulting in different degrees of damage to the surrounding ancillary buildings. In order to study the impact of hydraulic fracturing on ancillary buildings, the finite element software ABAQUS was used to establish a three-dimensional model of middle and high-rise isolated structures to simulate the earthquake triggered by hydraulic fracturing. Then, considering the SSI (soil-structure interaction) effect of soil-based structure, the nonlinear dynamic response of the structure under the action of ground motion was analyzed. Through the adoption of different types of soil and the foundation depth, the influence of various parameters is discussed. The study found that in the case of not considering SSI, basal shear force, and displacement between floors of the seismic-isolation structure significantly greater than considering SSI, using hard soil layer, base shear displacement is greater than the soft soil layer and interlayer, shows that due to the effect of hydraulic fracturing, making fluid diffusion in soil, the seismic energy dissipation effect. It is also found that the period, base shear, peak displacement, and interlayer displacement of deep foundation pit are increased compared with shallow foundation pit considering SSI effect.

Impacts of Hydraulic Fracturing on Surface and Groundwater Water Resources: Case Study from Louisiana

Hydraulic fracturing activities have been gaining more attention; therefore, a better understanding of the potential stress that fracturing may cause to freshwater resources is needed. The goal of this study is to assess the impact of current and projected future water demands for hydraulic fracturing on water resources in two main shale plays in the US state of Louisiana: the Haynesville shale and the Tuscaloosa Marine shale. The study analyzes historical and future projected fracturing scenarios that simulate different extraction rates over the two shale plays. In each fracturing scenario, stresses on both surface and groundwater are evaluated separately using the Water Supply Stress Index (WaSSI). Under all scenarios, the impact of fracturing water demands on surface water resources is within the low-stress category in most watersheds in both shale plays. In contrast, groundwater resources appear to be highly vulnerable under all fracturing scenarios. The results suggest that nongroundwater resources in Louisiana’s shale plays should be used for fracturing activities instead of groundwater whenever possible. The results provide a quantitative assessment of the current and future water stress due to fracturing and have important implications for regional water allocation and management policies.

Impact of Hydraulic Fracturing on Productivity of Gas Condensate Wells

Having an increase in the discovery of gas reservoirs all over the world, the most common problem related to gas condensate wells while producing below dew point condition is condensate banking. As the bottom hole pressure drops below the dew point, the liquid starts to exist and condensate begins to accumulate. Relative permeability of gas will be reduced as well as the well productivity will start to decline. The effect of applying a hydraulic fracture to gas condensate wells is the main objective of this paper. A compositional simulator is utilized to investigate the physical modifications that could happen to gas and condensate during the production life of an arbitrary well. Performing a good designed hydraulic fracture to a gas condensate well typically enhances the production of such well. This increase depends basically on certain factors such as non-Darcy flow, capillary number and capillary pressure. Non-Darcy flow has a dominant impact on gas and condensate productivity index after performing a hydraulic fracture as the simulator indicates. The enhancement of gas and condensate production can be obtained for gas condensate reservoirs in which the reservoir pressure is above or around the dew point pressure to have a margin for the pressure to decline with time and also eliminate the probability of forming condensate in the reservoir. On the other hand if the reservoir pressure is below the dew point pressure, there will be definitely a condensate in the reservoir and a specific design for the hydraulic fracture is a must to get the required enhancement in the production.

Impact of hydraulic fracturing and borehole spacing on gas drainage along a coal seam

Hydraulic fracturing is a technology employed to improve coal seam permeability and gas drainage. This study uses theoretical analysis and field testing to examine the mechanisms of hydraulic fracturing of a coal seam, including the initiation conditions of boreholes and cracks, main crack forms, and expansion and extension processes. RFPA2D-flow software was used to develop a numerical simulation of double-hole hydraulic fracturing, from crack initiation to expansion and extension in the coal body. The numerical simulation revealed characteristics and evolution of the stresses, water pressure and acoustic emission around the boreholes and estimated the permeability improvement range of fracturing holes under conditions of different hole spacing. Results of a field industrial test showed that the daily gas drainage pure flows increased by 5.8-17.6 times, the average gas drainage velocity reached 3.76 m3/min (maximum 10 m3/min), the gas drainage rate of the working face reached 57.32%, and the influence radius of single-hole hydraulic fracturing is approximately 5 m. This study demonstrates that hydraulic fracturing and permeability improvement technology can greatly improve the gas drainage rate of boreholes in a coal seam.

Impact of hydraulic fracturing and borehole spacing on gas drainage along a coal seam

Hydraulic fracturing is a technology employed to improve coal seam permeability and gas drainage. This study uses theoretical analysis and field testing to examine the mechanisms of hydraulic fract...

Impact of hydraulic fracturing on cement sheath integrity; A modelling approach

Recent arguments about the possibility of well leakage and underground water pollution in particular regions have raised significant concerns regarding wellbore integrity during hydraulic fracturing in shallow formations. In this paper, we take a look at the containment of annulus cracks that might develop during hydraulic fracturing treatments. Wellbore integrity is highly dependent on the integrity of the bonding between the cement and the formation as well as the bonding between casing and cement. Cement heterogeneity results from unsmooth borehole surfaces, complex geological conditions, mud cakes, and cement contamination. Excessive fluid pressure during hydraulic fracturing not only provides the driving force for the initiation and propagation of fractures in the reservoir, but also in special cases, it may lead to fracture propagation around the casing, i.e. annulus cracks. A coupled three-dimensional poroelastic model with embedded cohesive zones is introduced here to simulate different fracture propagation scenarios that may occur in vertical and horizontal wells during hydraulic fracturing stimulations in cased-hole zones. The cohesive layer theory is utilized to model the initiation and propagation of transverse, longitudinal and delamination fractures. Using the numerical analysis provided in this paper, a few hydraulic fracturing cases were simulated by taking advantage of the treatment pressure data and petrophysical logs, and the results were compared with the post-treatment radioactive tracer logs available for these wells.

Scenario analysis for assessing the impact of hydraulic fracturing on stream low flows using the SWAT model

ABSTRACTScientists and water users are concerned about the potential impact on water resources, particularly during low-flow periods, of freshwater withdrawals for hydraulic fracturing (fracking). Therefore, the objective of this paper is to assess the potential impact of hydraulic fracturing on water resources in the Muskingum watershed of Eastern Ohio, USA, especially due to the trend of increased withdrawals for hydraulic fracking during drought years. The Statistical Downscaling Model (SDSM) was used to generate 30 years of plausible future daily weather series in order to capture the possible dry periods. The data generated were incorporated in the Soil and Water Assessment Tool (SWAT) to examine the level of impact due to fracking at various scales. Analyses showed that water withdrawal due to hydraulic fracking had a noticeable impact, especially during low-flow periods. Clear changes in the 7-day minimum flows were detected among baseline, current and future scenarios when the worst-case scenario was implemented. The headwater streams in the sub-watersheds were highly affected, with significant decrease in 7-day low flows. The flow alteration in hydrologically-based (7Q10, i.e. 7-day 10-year low flow) or biologically-based (4B3 and 1B3) design flows due to hydraulic fracking increased with decrease in the drainage area, indicating that the relative impact may not be as great for higher order streams. Nevertheless, change in the annual mean flow was limited to 10%.

Contracted Fracking: Using Community Contracts to Mitigate Local Impacts of Hydraulic Fracturing

Contracted Fracking: Using Community Contracts to Mitigate Local Impacts of Hydraulic Fracturing

Modeling of impact of hydraulic fractures on the process of fluid displacement from low-permeability sedimentary rocks

Mathematical modeling of fluid displacement from low­permeability (shale) sedimentary rocks in the pattern waterflooding elements considering the impact of hydraulic fractures is performed. Based on numerical methods of comprehensive analysis (quasiconformal mappings), numerical algorithms for the calculation of filtration characteristics: saturation field, velocity quasipotential, time of the displacing fluid breakthrough to the production well and its complete waterflooding are developed. The algorithm also allows determining the coordinates of the critical “suspension” points and their quasipotential values, fluid interface position at different time points, the overall filtration rate of the production well, the dependence of oil fraction in it. For an effective analysis of the research, calculations of the volume of the displaced fluid in the reservoir within a certain time and the volume of the remaining fluid in the reservoir at an arbitrary time are performed. This allowed predicting the rate of waterflooding of production wells and identifying the features of operation under the projected arrangement of wells and hydraulic fractures on them. It was found that the “transverse direction” (with respect to injection wells) of hydraulic fractures accelerates the time of the displacing reagent breakthrough to the production well (although provides some growth of oil withdrawal values at the initial stages), and their “longitudinal” direction reduces the number of oil stagnation zones.

Анализ и пути повышения эффективности механизированной добычи нефти из малодебитных скважин в кризисных условиях

The article deals with the current state of the petroleum industry. The typical schedule of oilfield development stages in Western Siberia is presented. The paper finds that the main reason for reduced effectiveness of the oilfield development is a rapid growth of water cuttings of well production. Low oil recovery factor (ORF) for the fields in Western Siberia (35 %) and the impact of hydraulic fracturing on the drowning rate are indicated. A comparative analysis of the mechanized facility reserves of the United States and the Russian Federation is given. The marginal well reserve of the USA with oil production rate up to 0.39 t/day is found to be operated with oil well pumps (OWP), while electrical submersible pump units (ESPU) are mainly applied for marginal wells in Western Siberia of the Russian Federation. The efficiency factor (EF) of electrical submersible pump units with rated capacity of 20 to 40 m 3 /day is lower than that of oil well pumps; it results in additional operational costs for oil production and increasing its prime cost. There is a breakthrough technology enabling a multiple increase of oil recovery factor by means of well drilling with horizontal tailing-in and branch holes at inactive well stock at the final oil field development stages. The use of oil well pumps in these wells (without large-scale hydraulic fracturing) will improve long-term profitability of oil production. The necessity of further application of OWPs and improving the control station to enable energy efficiency and optimal well performance is substantiated.

Origins of Natural Gas Discharging From Shallow Groundwater

Beyond the Headlines Editor’s note: Professionals in the oil and gas industry often receive questions about how industry operations affect public health, the environment, and the communities in which they operate. Of particular concern today is the impact of hydraulic fracturing on the environment. In this column, JPT invites energy experts to put those questions and concerns about industry operations into perspective. Additional information about the oil and gas industry, how it affects society, and how to explain industry operations and practices to the general public is available on SPE’s Energy4me website at www.energy4me. org. In my recent article in the July issue of JPT, I explained how the composition of natural gas establishes a basis for differentiating between thermogenic and biogenic gases. Recall that thermogenic gases are formed from the heating of organic matter in high-temperature subsurface environments. Gases that form under these conditions are typically composed of hydrocarbons ranging from one to six carbon atoms, or methane (C1) to hexane (C6). Biogenic gases form in lower temperature regimes, usually in the near subsurface, as a result of microbial activity on buried organic matter. These gases, which are dominantly methane with very minor ethane (C2) and propane (C3), are commonly associated with coalbeds, swamps, and landfills. We can differentiate between thermogenic and biogenic gases by considering the molar ratio of methane to ethane and other hydrocarbons (C1/( C2+ C3). As noted in my previous article, it is not uncommon for that ratio to be less than 100 among thermogenic gases and to be greater (oftentimes, much greater) than 1,000 among biogenic gases. The difference in ratios is a function of the deficiency of ethane (C2), propane (C3), and higher-chain hydrocarbons in biogenic gases. In addition to the molar ratios, geochemistry offers a deeper look into the signatures of natural gases by mass spectrometry. This gives geochemists a powerful means of differentiating between thermogenic and biogenic gases. Specialized laboratories have the equipment needed to conduct such analyses on samples of dissolved gas in water and samples of gas collected from production wells. Such analyses focus on specific carbon and hydrogen components of the methane (C1) fraction.

Fracturing and Natural Gas in Groundwater: Is There a Connection?

Beyond the Headlines Editor’s note: Professionals in the oil and gas industry often receive questions about how industry operations affect public health, the environment, and the communities in which they operate. Of particular concern today is the impact of hydraulic fracturing on the environment. In this column, JPT invites energy experts to put those questions and concerns about industry operations into perspective. Additional information about the oil and gas industry, how it affects society, and how to explain industry operations and practices to the general public is available on SPE’s Energy4me website. Anyone who has watched films such as Gasland and Promised Land is aware of the alleged dire consequences to groundwater resources from the petroleum industry’s decades-old practice of hydraulic fracturing of tight formations to release hydrocarbons. Gasland (a “documentary”) and Promised Land (a movie starring Matt Damon) purport to expose such threats, which are highlighted in the form of natural gas discharging from groundwater or flares from the kitchen faucets of landowners whose water wells are located near fields with recently fractured wells. Such representations are intended to create the impression that fracturing opens pathways from deeply buried strata for the migration of natural gas, brine, and drilling fluids to shallow formations that are sources of groundwater for cities and rural areas where fracturing is a common method for oil and gas extraction. The print and broadcast media are complicit in the matter, as both have piled on to fan the sentiment of Americans against this method of developing much needed natural gas resources. A consequence of antifracturing films and reporting is confusion among the public and attempts by environmentalists to ban fracturing. Origins of Natural Gas Natural gas is derived from different sources. Most of what we think of as natural gas is produced within the deep subsurface under high- temperature and high-pressure conditions (thermogenic gas). A much smaller component is derived from the production of gas in the shallow subsurface under lowtemperature and low-pressure environments (biogenic gas, that is, coal beds, swampy environments, and landfills). Geochemists can differentiate between thermogenic and biogenic gases by looking at their carbon compositions (as illustrated by gas chromatographs) and their carbon and hydrogen isotope signatures. This column focuses on the role of gas chromatography as a differentiator of biogenic and thermogenic gases. Carbon and hydrogen isotope ratios will be the subject of another column. Gas Chromatography Because of the different environments in which natural gases are generated, thermogenic gases and biogenic gases can be expected to have distinct compositions. All hydrocarbons are carbonbased compounds with the number of carbon atoms of the components ranging from one to as many as 30 (C1 to C30). For our purposes, we are interested only in those components with one to six (C1 to C6) carbon atoms, which are methane through hexane, respectively. Biogenic gases are primarily methane (C1) and very little ethane (C2) and, in some cases, propane (C3), with methane usually accounting for 99% or more of total gas. Thermogenic gas consists of measurable components of fractions heavier than methane (that is, C2 through C6 gases). The difference between thermogenic and biogenic gases is illustrated in Fig. 1, which shows the composition of the gas samples collected from the groundwater of the Wilcox aquifer and produced-gas samples from nearby fractured wells that were thought to have been the source of natural gas in the aquifer, approximately 10 miles north of Shreveport (Caddo Parish), Louisiana. The figure shows the percentage (by mass) of each hydrocarbon and nonhydrocarbon gases detected in the samples.

Comments: EPA Examines Hydraulic Fracturing

Editor's column Last month, the US Environmental Protection Agency (EPA) issued a long-awaited study concerning the potential impact of hydraulic fracturing on drinking water. The US Congress had ordered the study in 2010 based on public concerns that the technique, rapidly growing in use, was causing environmental problems, including threats to water supplies. The report took a relatively balanced approach, noting that there have been some problems, but they have been small in scale compared with the number of wells fractured during the study period. “We did not find evidence that these mechanisms (hydraulic fracturing) have led to widespread, systemic impacts on drinking water resources in the United States,” the study said. “Of the potential mechanisms identified in this report, we found specific instances where one or more mechanisms led to impacts on drinking water resources, including contamination of drinking water wells. The number of identified cases, however, was small compared to the number of hydraulically fractured wells.” Different groups saw the study’s conclusions differently, with the bias in the eye of the beholder. A brief survey of website and newspaper headlines bears this out: EPA: Fracking Tainted Drinking Water, but Problems Not Widespread (U.S. News & World Report) EPA report: Fracking no harm to drinking water (Florida Times-Union) EPA: Fracking poses risk to water supply (Albany Times Union) EPA Fracking Report Leaves Both Sides Claiming Victory (OilPrice.com) EPA says new study doesn’t show fracking is safe (Charleston Gazette) In the study, the EPA examined more than 3,500 published technical papers, journal articles, and industry articles, as well as reports done by federal and state governments, nongovernmental organizations, and industry groups. EPA officials also said they conducted additional tests and research, which led to more than 20 peer-reviewed papers. This is not the final version of the report, titled “Assessment of the Potential Impacts of Hydraulic Fracturing for Oil and Gas on Drinking Water Resources.” The draft is now available for public comment and will be reviewed by a board of scientists, with the final report due next year. An executive summary and the full report can be found at www2.epa.gov/hfstudy. This is one of many reports likely to be issued over the next several years on hydraulic fracturing and its effect on the environment and surrounding communities. In addition to water, concerns have been raised about fracturing’s relationship to earthquakes and air emissions. Over the past year, JPT has been publishing a series titled “Beyond the Headlines” that attempts to put industry issues such as fracturing in perspective. Among the topics addressed so far include wastewater disposal, earthquakes, well construction practices, and the amount of water used in fracturing. These columns can be found in JPT’s archives online at www.spe.org/ jpt. Additional resources about hydraulic fracturing practices are available on SPE’s energy4me.org website. JPT

Are Well Construction Practices Safe for the Environment?

Beyond the Headlines Editor’s note: Professionals in the oil and gas industry often receive questions about how industry operations affect public health, the environment, and the communities in which they operate. Of particular concern today is the impact of hydraulic fracturing on the environment. In this new column, JPT is inviting energy experts to put those questions and concerns about industry operations into perspective. Additional information about the oil and gas industry, how it affects society, and how to explain industry operations and practices to the general public is available on SPE’s Energy4me website at www. energy4me.org. There are headlines every day that discuss the ethics and safety behind oil and gas operations, particularly hydraulic fracturing. According to the media, hydraulic fracturing can cause earthquakes, contaminated water, and even deformity in animals (if you believe the movie Promise Land). The truth behind the headlines is that hydraulic fracturing is a safe way to get natural gas out of the ground. What makes it a safe practice is solid well construction. The evolution of oil and gas well construction has passed through many frontiers with each new foray into the next “unconventional” hydrocarbon resource generating the needed technology to keep pace with the immediate needs. In light of more than 4 million wells drilled in North America over the past 194 years, it is somewhat surprising that the industry has been successful so many times, and what we have done with lessons learned from the relatively few failures. Wells are designed from the bottom to the top and from the inside outward, but they are drilled and constructed in exactly the opposite manner—often by practitioners with metrics different from the initial design principles. The fundamental objective that must shape every action along the way is that the final product of well construction must be a highly durable pressure vessel, albeit one that is composed of hundreds of threaded connections with a variety of seals and with a long coat of cement. Few other engineering disciplines operate in this highly cloaked area, in which the final engineering product, the downhole section of the well, cannot be conventionally seen, heard or touched, and produces a product that no one really wants to smell or taste. The birth of the US gas industry was ushered in by William Hart’s shale gas well in Fredonia, New York, in 1821. He encountered flowing gas at 28 ft and, consistent with the technology of the time, cased it with wood and flowed shale gas through wood and early steel pipes to light the streets and buildings previously illuminated with lamps filled with whale oil.

Can Waste Water Be Disposed of Safely?

Beyond the Headlines Editor’s note: Professionals in the oil and gas industry often receive questions about how industry operations affect public health, the environment, and the communities in which they operate. Of particular concern today is the impact of hydraulic fracturing on the environment. In this new column, JPT is inviting energy experts to put those questions and concerns about industry operations into perspective. Additional information about the oil and gas industry, how it affects society, and how to explain industry operations and practices to the general public is available on SPE’s Energy4me website at www. energy4me.org. Shale oil and gas wells use a lot of water in fracturing operations. Each well may use up to 8 million gallons, and as much as 35% of this can return as flowback water. Safe disposition of this waste water is an industry priority especially because of the widely reported past missteps in Pennsylvania. Safe disposition is completely feasible and, in fact, is being broadly practiced today. The Nature of Flowback Water Even if fresh water is used as the base fracturing fluid, what returns to the surface is salty. This is because the water found in association with hydrocarbons has high salinity. Shale oil and gas flowback water salinity typically range from 16,000 parts per million (ppm) to more than 300,000 in some instances. For comparison, sea water runs around 35,000 ppm. The chemicals introduced into the fracturing fluid will also be present in some proportion. These will be low in concentration because even the original fracturing fluid contains only up to about 0.5% chemicals. Finally, one could also encounter species present in subterranean rock. These could include aromatic compounds (such as benzene) and radioactive species. Some state regulations, such as the ones pending in North Carolina, prohibit the use of aromatics in fracturing fluid so, if present, they could only have come from the subsurface. The same holds for radioactive species. In most instances, subterrestrial bacteria will also be present. All of these render the flowback water unsuited for direct discharge. Re-use of Flowback Water Flowback water may be reused to formulate fracturing fluid for the next operation. But since only about a third of injected water returns, additional water is needed (makeup water). In the early going, reuse was rendered costly due to the need to desalinate down to fresh water. However, more recently, all service companies have announced that they can tolerate salinities in excess of 250,000 ppm.

How Safe Is Our Drinking Water?

Beyond the Headlines Editor’s note: Professionals in the oil and gas industry often receive questions about how industry operations affect public health, the environment, and the communities in which they operate. Of particular concern today is the impact of hydraulic fracturing on the environment. In this new column, JPT is inviting energy experts to put those questions and concerns about industry operations into perspective. Additional information about the oil and gas industry, how it affects society, and how to explain industry operations and practices to the general public is available on SPE’s Energy4me website at www. energy4me.org. Do shale oil and gas drilling present a real threat to drinking water supplies? This is likely the single greatest concern in the minds of those opposed to the exploitation of this resource. Can oil and gas wells leak fluids into the Earth? Yes. Can it be prevented? Yes, again. In this essay, we will discuss the mechanisms involved, the measures to prevent these occurrences, and the most recent scientific studies on the topic. On the last point, I am happy to report that, to date, the news is uniformly very good. Happy because this resource must be developed in a sustainable fashion. It has transformed the United States economy and improved the lot of every US citizen. We have a duty to get it done right. Other countries with similar resources need the US to succeed. There are two potential sources for contaminating fluids. One is the hydraulically fractured zone in the reservoir and the other is the vertical portion of the wellbore. Microseismic monitoring involves “listening” to the minor tremors generated by the hydraulic fracturing operation. Thousands of such operations have been monitored and fractures do not extend more than 1,000 ft in a vertical direction. Leaving a margin of error, 2,000 ft of vertical separation ought to be sufficient. Most producing zones are at vertical depths greater than 4,000 ft and fresh water rarely extends beyond a few hundred feet. Another measure of comfort comes from the propensity of rock fractures to “heal” due to Earth stresses. This tendency is the reason that proppants (sand or other ceramic material) are used to keep the cracks in producing zones open to allow fluid to flow into the well. This propping mechanism is not dissimilar to the piers and beams used in coal mines. The most definitive study (Hammack et al. 2014) in this regard is one by the US Department of Energy in the Marcellus Shale. Researchers injected tracers during the fracturing operation and found no evidence in freshwater bodies above. Studies of Potential Contamination of Fresh Water Two types of fluids are candidates for leaking into surrounding rock: gases and liquids. One is produced gas and the other is produced liquids, including portions of the fracturing fluid returning to the surface. In general, gas is able to move through the formations more easily than liquids. Consequently, if gas infiltrated freshwater bodies, this would have little bearing upon the possibility of liquid contamination. This point has been evident in all of the studies reported to date. In a 2011 paper, Osborn et al. reported methane contamination of water wells in proximity to shale gas wells in Pennsylvania, but found no liquid contaminants. This study did not have baseline measurements. A later 2012 study (Kresse et al.), with baseline measurements, together with US Geological Survey investigators, reported that neither type of fluid contaminant was found in proximal freshwater bodies. In 2014, Darrah et al. studied several existing wells in Pennsylvania and Texas using isotopes of noble gases as tracers. They found methane contamination of water wells, but concluded that in all instances, it was because of faulty well construction. They ruled out direct contamination from the fractured intervals (see story on page 42). All the four studies support a longheld industry belief that properly constructed wells are not likely to leak fluids. An upset condition is far more likely to result in methane, rather than liquid, contamination. This is important because methane in drinking water has no adverse health effects. Public concerns center on potential contamination from the ingredients in fracturing fluid. The studies to date offer considerable comfort in this area.

Environmental Impacts of Hydraulic Fracturing

Frank R. Spellman The author or the publisher appears to have chosen this title because of the recent prominence of hydraulic fracture stimulation (“fracking”). A book published in early 2013 that purports to address the environmental impacts of fracking of unconventional gas resources might be expected to at least summarize the environmental issues and regulations that were of importance by late 2011 when the Marcellus, Barnett and other shale gas plays were under full development. However, this book does not meet that criterion. For example, you won't find anything here about the controversy that developed in the pages of the Proceedings of the National Academy of Sciences (PNAS) in late 2011 over the suspected effects of hydraulic fracturing on domestic wells in Pennsylvania, e.g., the work of the Duke University team (Osborn et al., 2011), and the rebuttals by Cabot Oil & Gas of Pittsburgh (Molofsky et al., 2011) and various academics (e.g., Davies, 2011). The Duke team presented data collected from domestic or other private wells completed in bedrock in northeastern Pennsylvania and adjacent New York State. They reported a strong correlation of dissolved methane concentrations …