Last data update: Apr 29, 2024. (Total: 46658 publications since 2009)
Records 1-14 (of 14 Records) |
Query Trace: Schatzel S[original query] |
---|
Implications of shale gas well integrity failure near a longwall mine under shallow cover
Ajayi KM , Khademian Z , Schatzel SJ , Rubinstein EN . Min Metall Explor 2023 This study simulates the impact of a shale gas well casing breach near a longwall mine. Field studies are conducted to measure mining-induced permeability changes over the abutment pillar of a longwall mine, and a geomechanical model is developed in 3DEC, a three-dimensional numerical modeling code, to predict the aperture of fractures in the overburden at the study site. The predicted aperture values are used to determine mining-induced permeabilities and the results are compared with the field measurements. These aperture values are provided as inputs into fracture flow code (FFC), which generates a stochastic discrete fracture network (DFN) model for the study site and predicts the potential shale gas flow to the mine. Results from 100 DFN realizations are statistically analyzed using the bootstrapping method to compensate for notable variation in fracture geometry. The results show a significant difference between the gas inflow for nearby panels due to increase in the induced permeability during mining of the second panel. The average gas flow to the mine was calculated as 4.72×10−2 m3/s (49 cfm) for a hypothetical breach at the Sewickley horizon during the first panel mining, 8.97×10−3 m3/s (19 cfm) for a hypothetical breach at the Uniontown horizon during the first panel mining, 2.16×10−1 m3/s (458 cfm) for a hypothetical breach at the Sewickley horizon during the second panel mining, and 8.07×10−2 m3/s (171 cfm) for a hypothetical breach at the Uniontown horizon during the second panel mining. Depending on the mine ventilation system, this could result in methane concentrations exceeding regulatory limits. Hence, these findings provide insights into the potential risk of an unconventional gas well casing breach near a longwall mine under shallow cover. © 2023, This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply. |
Evaluation of parameters influencing potential gas flow to the mine in the event of a nearby unconventional shale gas well casing breach
Ajayi KM , Khademian Z , Schatzel SJ . Min Metall Explor 2022 39 (6) 2333-2341 The integrity of unconventional shale gas well casings positioned in the abutment pillar of a longwall mine could be jeopardized by longwall-induced deformations. Under such scenarios, the surrounding fracture networks could provide pathways for gas flow into the mine creating safety concerns. To provide recommendations for developing guidelines that ensure a safe co-existence of longwall mining and unconventional shale gas production, this study evaluates the impact of parameters that could affect potential shale gas flow into the mine in the event of a casing breach using a discrete fracture network (DFN) model. These parameters are evaluated using a conceptualized DFN realization that is representative of the fractured zone in the overburden, and the range of parameter variations is within values validated with field measurements. The results show that a decrease in fracture aperture (potentially due to longwall-induced stress in the likely vicinity of the breach location) reduces the potential gas flow to the mine by a significantly higher proportion. A 50% decrease in the aperture of the fracture that directly transports the gas from the casing breach location reduces the gas flow to the mine by over 70%. Similarly, changes in the fracture water saturation level significantly affect the gas flow. In all cases, the potential gas flow to the mine is higher if the casing breach occurs at an increased gas well pressure. These findings provide critical information regarding the impact of each of the parameters associated with gas flow in the event of a shale gas casing breach near a longwall mine and could help towards the development of guidelines to ensure a safe coexistence of both industries. © 2022, This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply. |
A discrete fracture network model for prediction of longwall-induced permeability
Ajayi KM , Khademian Z , Schatzel SJ , Watkins E , Gangrade V . Min Metall Explor 2022 39 (4) 1793-1800 Longwall-induced deformations could jeopardize the mechanical integrity of shale gas well casings positioned in the abutment pillar of a longwall mine. The in situ and induced fracture networks surrounding the gas well could provide pathways for gas flow into the mine creating safety concerns. Hence, this study by the National Institute for Occupational Safety and Health (NIOSH) develops a discrete fracture network (DFN) model to characterize the fractures in the overburden based on geomechanical analyses of mining-induced fracture apertures at a study site in southwestern Pennsylvania. The apertures from the geomechanical model are used to develop a stochastic DFN model of the site in fracture flow code (FFC). Multiple realizations of the stochastic DFN model that replicate potential fracture geometries are simulated, and the fracture permeability is compared with field measurements. A maximum field measurement of 5.03 1012 m2 (5080 mD) and 3.82 1013 m2 (386 mD) was estimated over the abutment pillar at the Sewickley and Uniontown horizon, respectively. The results show that the average permeabilities from the DFN model agree closely with the field measurements. In addition, the comparison of all the field measurements and 100 DFN realizations show the model is representative of field conditions. These findings provide critical information regarding fracture characteristics in the overburden, which will further be used to predict potential shale gas flow to the mine in the event of a casing breach for an unconventional gas well. 2022, This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply. |
Rockmass permeability induced by longwall mining under deep cover: Potential gas inflow from a sheared gas well
Khademian Z , Ajayi KM , Schatzel SJ , Esterhuizen GS , Kim BH . Min Metall Explor 2022 39 (4) 1465-1473 The stability of shale gas wells drilled through current and future coal reserves can be compromised by ground deformations due to nearby longwall mining. Depending on the longwall-induced rockmass permeability, the high-pressure explosive gas from the damaged well may reach mine workings and overwhelm the mine ventilation systems. This study uses geomechanical models to estimate the rockmass permeability induced by mining. A two-panel longwall model of a deep, 341-m-cover mining site in southwestern Pennsylvania is constructed in 3DEC to explicitly model the rockmass by a discrete fracture network (DFN) technique. Stress-induced fracture apertures and permeabilities are calculated across the model and are validated against permeability measurements. A fracture flow code (FFC) is developed to use these results to predict potential inflow to the mine should a gas well breach occur. One hundred DFN realizations are simulated, and the results show that for a gas pressure of 2.4 MPa, the average of the predicted inflow rates to this deep-cover mine is 0.006 m3/s, significantly lower than the average inflow of 0.22 m3/s for a shallow-cover mine (145-m deep) studied in the previous work (Khademian, et al. 2021). The result can help assess the potential hazards of a shale gas well breach for mine safety and evaluate the ventilation requirements to mitigate the risk. © 2022, This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply. |
Assessing Gas Leakage Potential into Coal Mines from Shale Gas Well Failures: Inference from Field Determination of Strata Permeability Responses to Longwall-Induced Deformations
Watkins E , Karacan CÖ , Gangrade V , Schatzel S . Nat Resour Res 2021 30 (3) 2347-2360 This paper summarizes the changes in permeability at three boreholes located above an abutment pillar at a longwall coal mine in southwestern Pennsylvania. The motivation of this study was to better characterize the potential interaction between shale gas wells and the mine environment, through measurement of permeability changes in the coal mine overburden caused by mining-induced deformations. Measuring permeability changes around boreholes affected by longwall mining is an effective method to indicate changes in the fracture network above longwall abutment pillars and estimate the capacity for gas flow from shale gas wells to the mine environment. This study measured permeability through falling-head slug tests at different longwall face positions during the mining of two longwall panels on either side of the test abutment pillar where the test boreholes were located. Three test boreholes were drilled to different depths above the active mining level, and they had screened intervals to evaluate the response of different stratigraphic zones to mining-induced stresses. The results showed that the permeability around the slotted intervals of each borehole increased pre-mining to post-mining, and the permeability increased from mining of the first longwall panel to mining of the second one, adjacent to the pillar. © 2021, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply. |
Transport model for shale gas well leakage through the surrounding fractured zones of a longwall mine
Ajayi KM , Schatzel SJ . Int J Min Sci Technol 2020 30 (5) 635-641 The environmental risks associated with casing deformation in unconventional (shale) gas wells positioned in abutment pillars of longwall mines is a concern to many in the mining and gas well industry. With the recent interest in shale exploration and the proximity to longwall mining in Southwestern Pennsylvania, the risk to mine workers could be catastrophic as fractures in surrounding strata create pathways for transport of leaked gases. Hence, this research by the National Institute for Occupational Safety and Health (NIOSH) presents an analytical model of the gas transport through fractures in a low permeable stratum. The derived equations are used to conduct parametric studies of specific transport conditions to understand the influence of stratum geology, fracture lengths, and the leaked gas properties on subsurface transport. The results indicated that the prediction that the subsurface gas flux decreases with an increase in fracture length is specifically for a non-gassy stratum. The sub-transport trend could be significantly impacted by the stratum gas generation rate within specific fracture lengths, which emphasized the importance of the stratum geology. These findings provide new insights for improved understanding of subsurface gas transport to ensure mine safety. |
A field study of longwall mine ventilation using tracer gas in a trona mine
Gangrade V , Schatzel SJ , Harteis SP . Min Metall Explor 2019 36 (6) 1201-1211 A ventilation research study was conducted by the National Institute for Occupational Safety and Health and a cooperating trona mine in the Green River basin of Wyoming, USA. The mine operation uses the longwall mining method in trona bed 17, a commonly mined unit in the region. The longwall face length is 228 m (750 ft), and caving on the face occurred up to the back of the longwall shields. The mine is ventilated using a main blowing fan and a bleeder shaft. For this study, sulfur hexafluoride (SF6) tracer gas was released in two separate monitoring experiments. For the first experiment, tracer gas was released on the face, this test focused on airflow along the longwall face of the active panel. Face test showed the airflow patterns to be more complex than just head-to-tail flow in the main ventilation air stream on the active panel. For the second experiment, tracer gas was released 2 crosscuts inby the face on the headgate side, this test focused on gas transport in the mined-out portion of the same active panel. Gob test showed a pathway of movement through the front of the active panel gob that moved outby from the tailgate corner. The primary pathway of tracer gas movement in the active panel gob was towards the headgate and tailgate bleeders and out of a bleeder shaft. The rate of movement towards the back of the gob was measured to be 0.19 m/s (37 fpm). |
Face ventilation on a bleederless longwall panel
Schatzel SJ , Gangrade V , Addis JD , Hollerich CA , Chasko LL . Min Metall Explor 2019 36 (3) 531-539 A ventilation study using tracer gas was conducted at a western US coal mine. The objective of the study was to evaluate the movement of longwall face air exchanges between the face and worked-out area and to document the presence or absence of face airflow pathways between these locations. The mine operator uses a bleederless longwall ventilation system with a back return and a blowing mine ventilation system. The study was conducted on an active panel and included both underground and surface monitoring sites. The study used sulfur hexafluoride (SF6) released as a slug on the longwall face and in the front of the gob inby the face. The velocity of the tracer gas movement in the gob was 0.019 m/s (3.7 fpm). The rate of movement for the overall tracer gas slug averaged about 0.0091 m/s (1.8 fpm). A separate tracer gas test initiated with the release of SF6 into the legs of the first shield showed the existence of more than one pathway of face air in the general direction from the headgate towards the tailgate corner. Maintaining adequate ventilation air on longwall faces is important for worker safety and for the dilution of methane emitted from the face and caved gob. A more detailed characterization of longwall system air and gas movement allows a mine to better assess its ventilation design for controlling gas on the face and in the gob. |
Investigating the impact of caving on longwall mine ventilation using scaled physical modeling
Gangrade V , Schatzel SJ , Harteis SP , Addis JD . Min Metall Explor 2019 36 (4) 729-740 In longwall mining, ventilation is considered one of the more effective means for controlling gases and dust. In order to study longwall ventilation in a controlled environment, researchers built a unique physical model called the Longwall Instrumented Aerodynamic Model (LIAM) in a laboratory at the National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Mining Research Division (PMRD) campus. LIAM is a 1:30 scale physical model geometrically designed to simulate a single longwall panel with a three-entry headgate and tailgate configuration, along with three back bleeder entries. It consists of a twopart heterogeneous gob that simulates a less compacted unconsolidated zone and more compacted consolidated zone. It has a footprint of 8.94 m (29 ft.) by 4.88 m (16 ft.), with a simulated face length of 220 m (720 ft.) in full scale. LIAM is built with critical details of the face, gob, and mining machinery. It is instrumented with pressure gauges, flow anemometers, temperature probes, a fan, and a data acquisition system. Scaling relationships are derived on the basis of Reynolds and Richardson numbers to preserve the physical and dynamic similitude. This paper discusses the findings from a study conducted in the LIAM to investigate the gob-face interaction, airflow patterns within the gob, and airflow dynamics on the face for varying roof caving characteristics. Results are discussed to show the impact of caving behind the shields on longwall ventilation. |
Methane emissions and airflow patterns on a longwall face: Potential influences from longwall gob permeability distributions on a bleederless longwall panel
Schatzel SJ , Krog RB , Dougherty H . Trans Soc Min Metall Explor Inc 2017 342 (1) 51-61 Longwall face ventilation is an important component of the overall coal mine ventilation system. Increased production rates due to higher-capacity mining equipment tend to also increase methane emission rates from the coal face, which must be diluted by the face ventilation. Increases in panel length, with some mines exceeding 6,100 m (20,000 ft), and panel width provide additional challenges to face ventilation designs. To assess the effectiveness of current face ventilation practices at a study site, a face monitoring study with continuous monitoring of methane concentrations and automated recording of longwall shearer activity was combined with a tracer gas test on a longwall face. The study was conducted at a U.S. longwall mine operating in a thick, bituminous coal seam and using a U-type, bleederless ventilation system. Multiple gob gas ventholes were located near the longwall face. These boreholes had some unusual design concepts, including a system of manifolds to modify borehole vacuum and flow and completion depths close to the horizon of the mined coalbed that enabled direct communication with the mine atmosphere. The mine operator also had the capacity to inject nitrogen into the longwall gob, which occurred during the monitoring study. The results show that emission rates on the longwall face showed a very limited increase in methane concentrations from headgate to tailgate despite the occurrence of methane delays during monitoring. Average face air velocities were 3.03 m/s (596 fpm) at shield 57 and 2.20 m/s (433 fpm) at shield 165. The time required for the sulfur hexafluoride (SF(6)) peak to occur at each monitoring location has been interpreted as being representative of the movement of the tracer slug. The rate of movement of the slug was much slower in reaching the first monitoring location at shield 57 compared with the other face locations. This lower rate of movement, compared with the main face ventilation, is thought to be the product of a flow path within and behind the shields that is moving in the general direction of the headgate to the tailgate. Barometric pressure variations were pronounced over the course of the study and varied on a diurnal basis. |
A study of leakage rates through mine seals in underground coal mines
Schatzel SJ , Krog RB , Mazzella A , Hollerich C , Rubinstein E . Int J Min Reclam Environ 2015 2015 (2) 165-169 The National Institute for Occupational Safety and Health conducted a study on leakage rates through underground coal mine seals. Leakage rates of coal bed gas into active workings have not been well established. New seal construction standards have exacerbated the knowledge gap in our understanding of how well these seals isolate active workings near a seal line. At a western US underground coal mine, we determined seal leakage rates ranged from about 0 to 0.036m3/s for seven 340 kPa seals. The seal leakage rate varied in essentially a linear manner with variations in head pressure at the mine seals. |
Methane emissions and airflow patterns along longwall faces and through bleeder ventilation systems
Krog RB , Schatzel SJ , Dougherty HN . Int J Min Miner Eng 2014 5 (4) 328-349 The National Institute for Occupational Safety and Health (NIOSH) conducted an investigation of longwall face and bleeder ventilation systems using tracer gas experiments and computer network ventilation. The condition of gateroad entries, along with the caved material's permeability and porosity changes as the longwall face advances, determine the resistance of the airflow pathways within the longwall's worked-out area of the bleeder system. A series of field evaluations were conducted on a four-panel longwall district. Tracer gas was released at the mouth of the longwall section or on the longwall face and sampled at various locations in the gateroads inby the shield line. Measurements of arrival times and concentrations defined airflow/gas movements for the active/completed panels and the bleeder system, providing real field data to delineate these pathways. Results showed a sustained ability of the bleeder system to ventilate the longwall tailgate corner as the panels retreated. |
A provenance study of mineral matter in coal from Appalachian Basin coal mining regions and implications regarding the respirable health of underground coal workers: a geochemical and Nd isotope investigation
Schatzel SJ , Stewart BW . Int J Coal Geol 2012 94 123-136 This study presents geochemical data produced from the analysis of coal and adjacent rock samples retrieved from coal mining regions in the U.S. to examine mineral matter provenance. Study sites included the Northern Appalachian Basin, where the units of interest were the Lower Kittanning Coal bed, the overlying Columbiana Shale, and the underlying paleosol (Allegheny Formation). Additional study sites were located in the Central Appalachian Basin, where sampling was conducted on strata associated with multiple coal beds of Middle and Lower Pennsylvanian age. The Central Appalachian Basin rock and coal samples were much lower in overall mineral matter and contained very little carbonate (calcite and siderite) or pyrite mineralogy, which was common at the Northern Appalachian Basin sites. Elemental analysis of rock samples indicated a trend of enrichment in Ca, Mg, Mn, Na, and K cations in the immediate overburden compared to the underlying rock in the Central Appalachian Basin. A similar trend was observed in coal related strata from the Northern Appalachian Basin which was attributed to epigenetic marine incursions. Rare earth element (REE) concentrations were determined in the samples, and showed Eu and Ce anomalies when normalized by chondritic values. The total REE content of the overburden is generally less than that of the underlying rock units. Neodymium isotopic analysis of the Lower Kittanning coal, overburden, and paleosol from the Northern Basin indicate partial resetting of the Sm–Nd system close to the time of deposition. The data indicate a common Appalachian source for the clastic mineral matter in the overburden, underclay, and coal mineral matter. The geochemical findings of this study may provide a viable method for distinguishing respirable dust sources in both Appalachian Basins. There are potential applications for this research to aid in the respiratory health of underground coal miners. |
An analysis of reservoir conditions and responses in longwall panel overburden during mining and its effect on gob gas well performance
Schatzel SJ , Karacan CÖ , Dougherty H , Goodman GVR . Eng Geol 2012 127 65-74 NIOSH conducted a cooperative research study to provide direct measurements of changing reservoir conditions in longwall panel overburden. The field measurements documented changes in permeabilities, methane concentrations, fluid pressures, and the effects of adjacent gob gas ventholes (GGVs) on NIOSH boreholes drilled in the study panel. Three different stratigraphic horizons were monitored by the NIOSH boreholes. Results indicated that the gob gas venthole fracture network formed 24 to 46m (80 to 150 ft) ahead of the mining face. Overburden permeabilities within the same overburden test zones were ~1md prior to undermining, increasing to hundreds or thousands of md during undermining. Permeabilities measured seven months after undermining showed additional increases. The relationship between changing reservoir conditions, longwall face position, and surface movement is discussed. Recommendations are made to optimize GGV performance by evaluating changes in subsidence produced by mining, resulting in rock stresses that substantially influence induced fracture permeability. Mechanisms to account for the observed changes in reservoir conditions are reported. |
- Page last reviewed:Feb 1, 2024
- Page last updated:Apr 29, 2024
- Content source:
- Powered by CDC PHGKB Infrastructure