Abstract Introduction Geologic Background Method Results Recorded vitrinite reflectance Subsidence history...

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2 Table of Contents Abstract... 3 Introduction... 4 Geologic Background... 7 Method... 8 Results Recorded vitrinite reflectance Subsidence history Thermal history Simple Burial Enhanced vertical heat advection Additional heat flow Discussion Simple Burial Enhanced fluid flow Lateral heat advection Conclusion Acknowledgement Works Cited Tables and Figures Appendices Ashcroft Svetz Westmoreland

3 Abstract Vitrinite reflectance isograds of Appalachian Basin, specifically in western Pennsylvanian, in Pennsylvanian and Devonian period comprises of two protruding salients with unusual vitrinite reflectance values (%Ro) of 0.8% to 2.5%. The anomalous thermal maturation due to unusual %Ro along these two protruding salients led to exploration of mechanisms that possible to explain the anomaly. Objectives of this study are: 1) creating a model that matches the recorded %Ro; and 2) exploring and analyzing the possible mechanism and their plausibility in explaining the unusual thermal maturation for both Pennsylvanian and Devonian. Three wells, Svetz, Ashcroft, and Westmoreland wells, located along one of the salients are analyzed. Subsidence history of sedimentary layer obtained from these wells is used as an input for the thermal model. The thermal model provides thermal history for each well. Vitrinite reflectance is then calculated using time and temperature from the thermal model. The models are created to test three possible mechanisms which are simple burial, vertical heat advection and lateral heat advection. Simple burial provides low modeled %Ro compared to recorded %Ro. Burial depth of 6km, 14km and 12km are needed for Ashcroft, Svetz and Westmoreland respectively to match the recorded %Ro. Vertical heat advection is explored with enhanced vertical fluid velocity. Ashcroft has a preferred enhanced velocity, v fp, of m/yr whereas Svetz has v fp of m/yr and Westmoreland has v fp of m/yr. However, vertical heat advection is only applicable to Pennsylvanian but not Devonian. Combination of fluid temperature of about 220 C and lateral fluid velocity of 10km/Myr results in modeled %Ro that matches the recorded %Ro. Direction of lateral flow also coincides with the shape of the protruding salients. Thus, lateral heat advection is a more plausible mechanism to provide additional heat flow and achieve the recorded %Ro. 3

4 Introduction Beginning with the work of Rodgers (1858), geologists have recognized that the organic rich sedimentary rocks of the Appalachian Basin indicate unusually high levels of thermal maturation. Since Rodgers, many others have reinforced this observation and have provided a wide range of ideas to explain the unusually high temperatures experienced by these rocks. Examples include Chyi et al. (1987), Hower and Rimmer (1991), Zhang and Davis (1993), Hulver (1997), Repetski et al. (2008) and Ruppert et al. (2010) that study the thermal maturation of coal in the Appalachian Basin especially in Devonian and Pennsylvanian. One of the most comprehensive studies has gathered all vitrinite reflectance value from multiple wells throughout the Appalachian Region to construct detailed thermal maturation map of Devonian black shales (Figure 1) by Repetski et al. (2008) and Pennsylvanian coal (Figure 2) by Ruppert et al. (2010). Compilation of vitrinite reflectance values from Chyi et al. (1987), Hower (1978), and Cole et al. (1979) contributes to the detailed map with abundant vitrinite reflectance values in Pennsylvanian. 4

5 Figure 1: Thermal map showing Devonian vitrinite reflectance isogradients in Pennsylvanian. The range of the isogradients is between 0.5% and 2.5% for the studied region. Closed circles on the map are recorded vitrinite reflectance values (Repetski et al., 2002) Figure 2: Thermal map of Pennsylvanian vitrinite reflectance isogradients. The range of the isogradients is between 0.8% and 1.8%. Closed circles on the map are recorded vitrinite reflectance values (Ruppert et al., 2010) 5

6 According to Figure 1 and Figure 2, there are two northwestward protruding salients with unusual vitrinite reflectance values (%Ro) implying anomalous thermal maturation in both Pennsylvanian and Devonian periods. Studies to explain this unusual thermal maturation developed many possible hypotheses. Rodgers (1858) attributes this anomaly to Mesozoic intrusives in the Gettysburg basin. In 1925, White hypothesized that the anomalous thermal maturation could be influenced by greatest horizontal compression due to tectonic stress. However, Teichmüller and Teichmüller (1966) argued that the anomaly is driven by temperature instead of the tectonic stress. Heck (1943) and Damberger (1974) proposed that the observed unusual coal thermal maturation could be related to telemagmatic heating from a hidden igneous source. This anomaly also picked up by Hulver (1997) and suggested that deep burial beneath a sedimentary thick cover could be the appropriate explanation contributes to uncommon high temperature. Tornegard (2010) investigated the hypothesis that lateral fluid migration contributed big part in thermal anomaly of the Devonian black shales. Therefore, this paper attempts to study and compare the anomalous thermal maturation in both Pennsylvanian and Devonian. Using burial history and initial conditions for the thermal structure of the crust and mantle, thermal histories are calculated for three wells in western Pennsylvania. The thermal histories lead to modeled %Ro that are compared with the observed %Ro near the well. This comparison provides the basis for exploring mechanisms that are possible in elevating the thermal maturation in both Devonian and Pennsylvanian. This lead to the purpose of this paper which is to use a thermal model in order to determine how much overheating occurred and then test three main suggestions for the overheating: 1) simple burial; 2) enhanced fluid advection of heat from below beginning at the time of deformation; and 3) lateral fluid advection of heat from the front of the orogenic wedge. 6

7 Geologic Background The Appalachian Basin is a foreland basin flanking the Appalahcian orogen that began it history in the Late PreCambrian as a passive margin basin of Laurentia. The Appalachian basin contains Paleozoic sedimentary rocks from Early Cambrian through Early Permian age (Ryder, 1995). The basin covers New York, Pennsylvania, eastern Ohio, West Virginia, western Maryland, eastern Kentucky, western Virginia, eastern Tennessee, northwestern Georgia, and northeastern Alabama (Ryder, 1995). Figure 3 illustrates location of Appalachian Basin. This study focuses on part of the Appalachian Basin province which is Pennsylvania. Figure 3: Location of the Appalachian Basin Provinces in the United States (Milici and Swezey, 2006) Pennsylvania is known for the Marcellus shale which is a potential source for natural gas. The vitrinite reflectance values shown in Figure 1 are the thermal maturation of Marcellus shale. 7

8 Other than the Marcellus shale, this region is also established with Pennsylvanian coal such as Pittsburgh coal. The vitrinite reflectance values in figure 2 represent the thermal maturation of Pennsylvanian coal. The thermal evolution for both Devonian and Pennsylvanian controls by the history of subsidence due to thinning followed by subsidence due to flexural loading of the Appalachian Basin. Method Data were collected from three different wells in conducting this study (refer to Figure 4 for the location of the wells). The Ashcroft, Svetz, and Westmoreland wells are located in Western Pennsylvania. Wells data show the stratigraphic thicknesses for the three wells from Cambrian to Pennsylvanian. The remainder of the stratigraphy, mainly the Permian, has been eroded, so range of estimated thicknesses provided by thermal studies of Appalachian Basin (Reed et al., 2005) is used. Figure 4: Location map for studied well in Western Pennsylvania. Ashcroft is located in Allegheny County, Westmoreland in Westmoreland County, and Svetz is situated in Somerset County. These three wells align along one of the protruding salients. 8

9 The stratigraphic data were then entered into a backstripping model (Cardozo, 2009) to generate a decompacted subsidence history of sedimentary layer, from which I then calculated the rates of subsidence throughout the history of each well. The backstripping model requires parameters such as the upper and lower well depth of a formation, age of the formation, density of sediment grains, the initial porosity, and a coefficient of porosity compaction. The subsidence histories then provided the basis for the calculation of the thermal history using SlugSed (Hutnak and Fisher, 2007). SlugSed is a one-dimensional thermal model that calculates heat flow and temperature in a column of compacting sediment given some boundary conditions that consist of the temperature at the surface, and thermal structure of the crust and mantle. The thermal structure of the crust and mantle comes from Jonas (2010), based on backstripping of the passive margin phase sediments. A general representation of the detailed heat flow calculation used in SlugSed shown in the following equation: This equation shows the sources of heat that were taken into consideration for SlugSed heat flow calculation except the horizontal advection part. Basically, the equation means changes in temperature over a small interval represent by δt/δ is influenced by heat flow attains from conduction, radiogenic heat production, vertical heat advection and lateral heat advection. v f in the vertical advection is enhanced vertical fluid flow velocity. v f presents in the horizontal 9

10 advection is the velocity of lateral fluid flow. This heat sources equation is a basis for the thermal model results that enable me to find the time-temperature histories of the Devonian and Pennsylvanian strata. These time-temperature histories then enable me to calculate the vitrinite reflectance using the Easy %Ro algorithm of Sweeney and Burnham (1990). This model essentially calculates an integral of the time and temperature history, summing up the effects of a series of chemical reactions involved in the transformation of organic material into progressively more ordered molecules that become aligned and reflect light more effectively as the transformation progresses. This calculation enables me to obtain the thermal maturation histories for both Pennsylvanian and Devonian in terms of vitrinite reflectance and to compare them to the recorded vitrinite reflectance for both periods. Results Recorded vitrinite reflectance Table 1 shows the recorded vitrinite reflectance (%Ro) values for both Pennsylvanian and Devonian. The Pennsylvanian %Ro and Devonian %Ro are anomalously high especially for Svetz and Westmoreland. Svetz has 1.40% and 2.75% for Pennsylvanian and Devonian respectively. Westmoreland recorded %Ro of 1.20% in Pennsylvanian and 2.50% in Devonian. This study tries to create models that match the recorded vitrinite reflectance of the three wells for both Pennsylvanian and Devonian. Subsidence history of sedimentary layer and thermal history obtained from Bckstrip model and SlugSed are the basis for these models. 10

11 Subsidence history Figure 5a, Figure 5b and Figure 5c are the subsidence histories of the sedimentary layer for Ashcroft, Svetz, and Westmoreland wells respectively. Drop down at around 299 million years ago for each layer occurred due to erosion of Permian layer. However, estimated thickness of the strata that have been removed by erosion is reconstructed (Rowan et al., 2004 and Reed et al., 2005). The subsidence histories models here also take two things into consideration for the reconstruction: 1) the layer has lower boundary conditions; and 2) relatively thin plate. Based on these conditions, Permian layer in the three wells are reconstructed to a maximum thickness of 5km due to uplifting based on Rowan et al. (2004) and Reed et al. (2005) to heat up the layer as hot as possible. The effect of this maximum burial can be seen in the thermal history. Thermal history 1. Simple Burial Lines with numbers shown in Figure 6a, Figure 6b, and Figure 6c are temperature distribution within the sedimentary layer over time for Ashcroft, Svetz and Westmoreland wells respectively. These thermal histories obtained from SlugSed are integrated with the subsidence histories to see the effect of simple burial, one of possible mechanisms for the unusual thermal maturation, of 5km on the thermal maturation for each well. Table 2 consists of the modeled and the recorded vitrinite reflectance of the three wells in Pennsylvanian. The modeled vitrinite reflectance values here are subjected to the simple burial. Based on table 2, the modeled vitrinite reflectance values of the three wells are lower compared to the recorded vitrinite reflectance. Ashcroft well differs by only 0.09% between the modeled and the recorded value. The other two wells have quite large differences. Svetz well differs by 11

12 0.70% and Westmoreland differs by 0.45% between the modeled and the recorded value. Since the vitrinite reflectance values do not match up, other possible mechanism is modeled and tested. 2. Enhanced vertical heat advection Figure 7a, Figure 7b and Figure 7c is combinations of the subsidence history and the thermal history for enhanced fluid velocity of m/yr. According to the equation shown before, vertical advection is one of the heat sources. Vertical heat advection refers to the transport of heat from below through fluid movement. The hot fluid velocities are manipulated to explore their effect on the thermal maturation history. Figure 8a, Figure 8b and Figure 8c demonstrate increment in hot fluid velocity that lead to increment of temperature through time. Table 3 shows the modeled %Ro and recorded %Ro for both Pennsylvanian and Devonian. Numbers in second column of table 3 illustrates the enhanced fluid velocities used to explore their effects on %Ro m/yr, m/yr and -0.01m/yr fluid velocities are common for the three wells. Negative sign in the values just indicates that the fluid flows are from below. Yellow boxes in the second column are the preferred enhanced fluid velocity that matches the modeled %Ro to recorded %Ro in Pennsylvanian. Each well has a different preferred enhanced fluid velocity, v fp. Ashcroft has v fp of m/yr, Svetz has v fp of m/yr and Westmoreland has v fp of m/yr. However, as these preferred fluid flow velocities are applied to the Devonian layer, the modeled %Ro do not match up with recorded %Ro in Devonian. Modeled %Ro for Svetz and Westmoreland wells are lower than the recorded %Ro. Additional heat flow is needed to further heat up the layer to the recorded %Ro. 12

13 3. Additional heat flow Figure 9a, 9b and 9c are the thermal history in Devonian for the three wells without any enhancement in vertical fluid flow. Blue line in each graph represents the modeled thermal history without any changes. Red line, on the other hand, represents the hypothetical thermal history with additional heat flow that achieves the recorded %Ro in Devonian. Temperature differences between the blue line and red line are different for the three wells. Ashcroft well only differs by about 5 C whereas Svetz and Westmoreland well differ by about 80 C. The heat flow for Svetz and Westmoreland to achieve the recorded %Ro are at about 220 C. This additional heat can be reached through the combination of fluid temperature and fluid velocity. Figure 10 shows combinations of fluid temperature and fluid velocity to achieve recorded %Ro of 2.50% for Westmoreland well. Non-linear relationship between the fluid temperature and the fluid velocity indicates that there are many other possible combinations to obtain %Ro of 2.50%. The fluid temperature of 220 C in Westmoreland well that corresponds to fluid velocity of 10km/Myr is an example from many other possible combinations. High temperature fluid flow with certain velocity signifies that there should be a heat source coming from outside to heat up the layer to the recorded %Ro. Discussion Simple Burial Hower and Davis (1981) and Hulver (1997) suggested deep burial beneath a thick sedimentary cover is the explanation for the unusual thermal maturation in the Appalachian Basin. Based on %Ro presents in table 2, the modeled %Ro did not match the recorded %Ro of 13

14 all three wells even though the burial depth is at maximum, 5km (Reed et al., 2005). In order to achieve the recorded %Ro, additional thickness of sediment must be deposited considering deeper burial is needed. Ashcroft well required 6km of Permian strata to achieve 0.80% in Pennsylvanian and 6.5km to achieve 0.90% in Devonian. Svetz well should comprise of 9km and 14km of Permian strata to achieve 1.40% and 2.75% in Pennsylvanian and Devonian respectively. Westmoreland well needs thicknesses of 8km and 12km of Permian strata to obtain the thermal history that corresponds to 1.20% in Pennsylvanian and 2.50% in Devonian respectively. So, this is not possible based on two explanations. First, the maximum thickness of reconstructed Permian strata is 5km based on Rowan and Reed. Second, location between wells is only 50 miles to each other and it is not possible to have a great difference in the Permian thickness in that small distances. Hence, the simple burial does not work in explaining the unusual thermal maturation. However, this method works perfectly well in illustrating the usual thermal maturation. Enhanced fluid flow Since the simple burial could not explain the unusual %Ro, another possible mechanism is explored. Giles (1987) suggests that the fluid movement with vertical velocity of less than 10mm/yr is a possible mechanism to increase the thermal maturation. The vertical flow of hot fluid is caused by progressive compaction of basin sediment. Difference in the preferred vertical fluid flow shown in table 3 is subjected to fracturing within the sedimentary layer. Andrews- Speed et al. (1984) proposed that the deep water flow is controlled possibly by the configuration of faults. Rome Trough, located in the Western Pennsylvania, is the basis for the enhancement in fluid velocity modeled in this study. Figure 11 illustrate the location of the Rome Trough. The 14

15 Rome Trough is a large graben filled with Cambrian and Lower to Middle Ordovician sediment that was created by eastern interior extension of Greenvile Basement (Kulander and Ryder, 2005). The Rome trough is characterized by early Paleozoic normal faults (Kulander and Ryder, 2005) and also thrust fault (Schumaker and Wilson, 1996). These faults, which are not active after the Middle Ordovician, were reactivated by Alleghanian compression later (Kulander and Ryder, 2005). So, these faults were possible to create fracturing within the sediment. Distances of the three studied wells from the Rome Trough are the fundamental of the preferred velocity fluid flow modeled. Svetz well, is the closest well to the Rome Trough. The small distances imply the fracturing within the sediment around the well is higher. This is the reason for the highest preferred vertical fluid flow, v fp, of m/yr. Westmoreland well, medium distances, has medium v fp, of m/yr and Ashcroft well, farthest from the Rome trough, has the lowest v fp, of m/yr. According to table 3, enhancement in vertical fluid flow did work for Pennsylvanian but not Devonian strata. Figure 12 demonstrates a clear picture of how the vertical heat advection mechanism functions. In this figure, hot fluid movement from the bottom sedimentary layer carries heat upwards. As a result, the upper sedimentary layer is heated up. However, the bottom layer is cooled down in response to the transfer of heat by the fluid flow. This illustration corresponds to Pennsylvanian and Devonian strata. Pennsylvanian is deposited on top of the Devonian. Thus, the vertical fluid flow transfers heat from the Devonian to Pennsylvanian strata. As a result, the Devonian layer is only heated up to a much lower temperature. Hence, the modeled %Ro of vertical heat advection with enhancement in fluid flow is lower than the recorded %Ro. 15

16 Lateral heat advection Higher recorded %Ro compared to modeled %Ro lead us to another possible mechanism that can suffice the additional heat flow called lateral heat advection. Daniels and Altaner (1990) hypothesized that the unusual thermal maturation pattern in Western Pennsylvania is a result of migration of hot fluids. The similar hypothesis is actually proposed before by Rodgers (1858). Rodgers suggested Mesozoic intrusive as the mechanism causes the anomalously high %R. However, it was not accepted because of the distances of the source from the studied well. Oliver (1986) described how the migration of hot fluid is possible. Figure 13 exemplifies the description by Oliver. The deforming thrust sheet, on the right side of Figure 13, due to mountain building squeezes hot fluids out. The hot fluids are then migrated to the foreland basin through permeable beds (Oliver, 1986). So, lateral heat advection is possible to explain the anomalous %Ro because of the migration of hot fluids. Figure 14 exhibits the effect of lateral heat advection on the geothermal gradient. Movement of hot fluids from outside of the studied well causes temperature of sedimentary layers to increase. In response, geothermal gradient also increases for moments, before it equilibrates, without any layer cooling down as we seen in the vertical heat advection mechanism. Therefore, lateral heat advection is more plausible in describing the anomalous thermal maturation in both Pennsylvanian and Devonian. Hypothetical thermal history with heat flow of about 220 C shown in Figure 9b and 9C is corresponds to study by Evan and Hobbs (2003). Evan and Hobbs (2003) suggested fluid temperatures between 160 C and >220 C based on evidence of fluid inclusions microthermometry they found. In addition, the range of fluid flow 16

17 velocity shown in Figure 10 (<50km/myr) is within the range of velocities of compactionally driven flow (Tornegard, 2010 and Giles, 1997). Besides, the shape of the two protruding salients shown in map (Figure 1 and Figure 2) is probably caused by the flow of hot fluid laterally. These two thermal bulges seen in the map coincide with Pittsburgh-Washington Structural Discontinuity trending northwest (Repetski et al., 2008). It is suggested that the Pittsburgh Washington Structural Discontinuity was the preferred structure of flow for warm to hot fluids (Repetski et al., 2008) in Devonian. Zhang and Davis (1993) picked up the same salients shapes in Pennsylvanian and interpreted this to be the fluid flow features too. In the future, permeability and porosity of preferred structure for fluid flow and their effects on the thermal maturation can be a good topic to study. Conclusion This study elucidates the complexity of thermal maturation history in Appalachian Basin. The anomalously high vitrinite reflectance not only observed in Devonian, but also Pennsylvanian strata. Simple burial is a doubtful mechanism to explain the unusual thermal maturity specifically in the Western Pennsylvania. But, usual thermal maturation can be finely described by the simple burial. In analyzing the anomalous thermal maturation, two mechanisms are explored: 1) Vertical heat advection; and 2) Lateral heat advection. However, the vertical heat flow only works for Pennsylvanian but not Devonian strata. Thus, lateral heat advection is more plausible in explaining the anomalous thermal maturation. Fluid temperature between 160 C and >220 C (Evan and Hobbs, 2003) and fluid velocity of less than 50km is needed to obtain the 17

18 unusually high vitrinte reflectance. Finally, this anomalously high thermal maturation is crucial in understanding the potential gas maturity in Appalachian Basin. 18

19 Acknowledgement I would like to thanks Dr David Bice for guiding and offering lots of advice to me in completing the study. His guidance and patience motivates me to give my best to the thesis study. I would like to thanks Dr Mark Patzkowsky too for putting a clear perspective about thesis project in class and giving guidelines that are helpful in completing the study. I would like to thanks friends and family too that always supports me. 19

20 Works Cited Andrews-Speed, C.P., Oxburgh, E.R. and Cooper, B.A. (Bulletin American Association of Petroleum Geologist) Temperatures and depth-dependent heat flow in western North Sea, Cardozo, Nester. (2009). Matlab Scripts.. Retrieved from Web: Christopher S. Kulander and Robert T. Ryder. (2005). Regional Seismic Lines Across the Rome Trough and Allegheny Plateau of Northern West Virginia, Western Maryland, and Southwestern Pennsylvania. US Geological Survey Open Report. Chyi, L.L., Barnett, R.G., Burford, A.E., et al. (1987). Coalification patterns of the Pittsburgh. Int. J. Coal Geol. 7, Cole, G.A., Williams, D.A., Smith, C.J.,. (1979). Regional coalification patterns for the coals of eastern Kentucky, Virginia, West Virginia, Ohio, Maryland, and southern Pennsylvania. West Virginia Geological and Economic Survey Open-File Report 57. Damberger, H. (1974). Coalification patterns of Pennsylvanian coal basins in the eastern United States. In: Dutcher, R.R., Hacquebard, P.A., Schopf, J.M., Simon, J.M. (Eds.). Carbonaceous Materials as Indictors of Metamorphism, vol Geological Society of America Special Paper, Daniels, E.J., Altaner, S.P. (1990). Clay mineral authigenesis in coal and shale from the Anthracite region, Pennsylvania. Am. Mineral. 75, Evans, M. a. (2003). Fate of 'warm' migrating fluids in the central Appalachians during the Late Paleozoic Alleghanian orogeny. J.Geochem.Explor., 78-9, , doi: /S (03) ER. Giles, M. (1997). Diagenesis : A quatitative perspective. Implications for Basin Modeling and Rock Property Prediction. Dordrecht: Kluwer Academic Publishers. Giles, M.R. (1987). Mass Transfer and the problems of secondary porosity creation in deeply buried hyrdocarbon reservoirs. Marine and Petroleum Geology, H.D., R. (1858). The Geology of Pennsylvania. First Geological Survey of Pennsylvania. Hower, J.C. (1978). Anisotropy of vitrinite reflectance in relation to coal metamorphism for selected United States coals. Unpublished PhD Dissertation, The Pennsylvania State University. Hower, J.C., Davis, Alan,. (1981). Application of vitrinite reflectance anisotropy in the evaluation of coal metamorphism. Geol. Soc. Am. Bull. 92, Hower, J.C., Rimmer, S.M. (1991). Coal rank trends in the central Appalachian coalfield. Org. Geochem. 17,

21 Hulver, M. (1997). Post-orogenic evolution of the Appalachian Mountain System and its foreland. Unpublished PhD dissertation, The University of Chicago, 1050 pp. Hutnak, M., and A.T. Fisher. (2010). Influence of sedimentation, local and regional hydrothermal circulation, and thermal rebound on measurements of seafloor heat flux, J. Geophys. Res., 112, B12101, doi: /2007jb Retrieved January, from Matweb Material Property Data: Jonas, M. E. (2010). Modeling the Thermal History of Appalachian Basin. Senior Thesis for Geosciences. Milici, R.C. and Swezey C.S.,. (2006). Assessment of Appalachian Basin Oil and Gas Resources: Devonian Shale-Middle and Upper Paleozoic Total Petroleum System:U.S. Geological Survey Open-File Report Oliver, Jack. (1986). Fluids expelled tectonically from orogenic belts; Their role in hydrocarbon migration and other geologic phenomenon. Geology, Reed et al. (2005). Burial and exhumation history of Pennsylvanian strata, central Appalachian basin: an integrated study. Basin Research, Repetski, J.E., Ryder, R.T., Weary, D.J., Harris, A.G., Trippi, M.H.,. (2008). Thermal Maturity Patterns (CAI and %Ro) in the Upper Ordovician and Lower-Middle Devonian Rocks of the Appalachian Basin: a Major Revision of USGS Map I-917-E Using New Subsurface Collections. U. S. Geological Survey Scientific Investigations Map SIM Rowan, E. L. (2006). Burial and Thermal History of the Central Appalachian Basin, Based on Three 2-D Models of Ohio, Pennsylvania and West Virginia. US Geological Survey. Rowan, E.L., Ryder, R.T., Repetski, J.E., Trippi, M.H., Ruppert, L.F.,. (2004). Initial Results of a 2D Burial/Thermal History Model, Central Appalachian Basin, Ohio and West Virginia. Retrieved from U.S. Geological Survey Open-File Report : Ruppert, L. F., J. C. Hower, R. T. Ryder, J. R. Levine, M. H. Trippi, and W. C. Grady. (2010). Geologic controls on thermal maturity patterns in Pennsylvania coal-bearing rocks in the Appalchian Basin. International Journal of Coal Geology, 81(3), ,doi: /j.coal Ryder, C. S. (2005). Regional Seismic Line Across the Rome Trough and Allegheny Plateau of northern west Virginia, western Maryland and southwestern Pennsylvania. US Geological Survey, 1-9. Ryder, R.T. (1995). Appalachian Basin Province (067). USGS. Shumaker, R.C., and Wilson, T.H.,. (1996). Basement structure of the Appalachian foreland in West Virginia; Its style and effect on sedimentation, in van der Pluijm, B.A., and Catacosinos, P.A., eds. Basement and basins of eastern North America: Geological Society of America Special Paper 308,

22 Sweeney, Jerry J., and Burnham, Alan K. (1990). Evaluation of a Simple Model of Vitrinite Reflectance Based on Chemical Kinetics (1). AAPG Bulletin, DOI: /0C9B251F D C1865D. Teichmüller, M., Teichmüller, R.,. (1966). Geological causes of coalification. In: Given, P.H. (Ed.). Coal Science. Amer. Chem. Soc. Advan.Chem, vol. 55, Tornegard, T. S. (2010). Anomalous thermal maturation patterns in Devonian shales in Western Pennsylvania: An update using new vitrinite reflectance data and heat flow. Senior Thesis in Geosciences. Zhang, E., Davis, A.,. (1993). Coalification patterns of the Pennsylvanian coal measures in the Appalachian foreland basin, western and south-central Pennsylvania. Geol. Soc.,

23 Tables and Figures Well Location Pennsylvanian %Ro Devonian %Ro Ashcroft Svetz Westmoreland Table 1: Recorded vitrinite reflectance of Pennsylvanian and Devonian strata for the three wells studied, Ashcroft, Svetz and Westmoreland. The recorded vitrinite reflectance in Devonian is higher than Pennsylvanian. Well Location Modeled Pennsylvanian %Ro Recorded Pennsylvanian %Ro Ashcroft Svetz Westmoreland Table 2: Modeled vitrinite reflectance is compared to recorded vitrinite reflectance in Pennsylvanian with Permian maximum burial of 5km. The modeled vitrinite reflectance is still low compared to recorded vitrinite reflectance. Enhanced fluid velocity Pennsylvanian Modeled %Ro Pennsylvanian Reported %Ro Devonian modeled %Ro Devonian Reported %Ro Well Location Ashcroft Svetz Westmoreland Table 3: Modeled vitrinite reflectance and reported vitrinite reflectance are compared for both Pennsylvanian and Devonian with enhancement in vertical fluid velocity. The negative sign for the enhanced velocity mean the fluid is flowing from below. Yellow boxes show the preferred vertical fluid velocity for each well and the modeled vitrinite reflectance corresponds to it. 23

24 Figure 5a: Subsidence history of the sedimentary layer for Ashcroft well without any enhancement in fluid velocity. This figure is created using the backstrip model. X-axis represents the time in million years from Cambrian to Permian. Y-axis represents the decompacted depth in kilometer. Drop down that occurs around 290 million years ago is due to Permian erosion. The subsidence history here takes into consideration of reconstruction of maximum burial depth of 5km in Permian. Subsidence history of Pennsylvanian layer starts around 310 million years ago whereas Devonian starts around 380 million years ago. Figure 5b: Subsidence history of the sedimentary layer for Svetz well without any enhancement in fluid velocity. Refer to figure 5b for detailed description 24

25 Figure 5c: Subsidence history of the sedimentary layer for Westmoreland well without any enhancement in fluid velocity. Refer to figure 5b for detailed description Figure 6a: Subsidence history of the sedimentary layer for without any enhancement in fluid velocity together with thermal history obtained from SlugSed for Ashcroft well. X-axis represents the time in million years from Cambrian to Permian. Y-axis represents the decompacted depth in kilometer. Numbers with horizontal colored lines are the temperature within the sediment through time. Temperature increases as colors of line with numbers change from blue to red or from top to bottom of the figure. Temperature and time obtained from this graph is applied to the Easy %Ro algorithm to determine vitrinite reflectance. 25

26 Figure 6b: Subsidence history of the sedimentary layer for without any enhancement in fluid velocity together with thermal history obtained from SlugSed for Svetz well. Refer to figure 6a for detailed description. Figure 6c: Subsidence history of the sedimentary layer for without any enhancement in fluid velocity together with thermal history obtained from SlugSed for Westmoreland well. Refer to figure 6a for detailed description. 26

27 Figure 7a: Subsidence history of the sedimentary layer for with m/yr enhancement in fluid velocity together with thermal history obtained from SlugSed for Ashcroft well. X-axis represents the time in million years from Cambrian to Permian. Y-axis represents the decompacted depth in kilometer. Numbers with horizontal colored lines are the temperature within the sediment through time. The highest temperature achieved in this stratigrpahy are greater compared to Figure 6a that does not have any vertical flow enhancement. The temperature gradient gets steeper at around 300 million years ago. Figure 7b: Subsidence history of the sedimentary layer for with m/yr enhancement in fluid velocity together with thermal history obtained from SlugSed for Svetz well. Refer figure 7a for detailed description. 27

28 Figure 7c: Subsidence history of the sedimentary layer for with m/yr enhancement in fluid velocity together with thermal history obtained from SlugSed for Westmoreland well. Refer figure 7a for detailed description. Figure 8a: Effects of different enhancement in vertical fluid flow to thermal maturation in Pennsylvanian. Numbers at the very left of the figure indicate the enhanced vertical velocity for Ashcroft well. X-axis represents the time in million years from Pennsylvanian to Permian. Y-axis represents the temperature that corresponds to the enhanced vertical velocity. As the enhanced vertical velocity increases, the temperature also increases through time. 28

29 Figure 8b: Effects of different enhancement in vertical fluid flow to thermal maturation in Pennsylvanian. Numbers at the very left of the figure indicate the enhanced vertical velocity for Svetz well. Refer to figure 8a for detailed description. Figure 8c: Effects of different enhancement in vertical fluid flow to thermal maturation in Pennsylvanian. Numbers at the very left of the figure indicate the enhanced vertical velocity for Westmoreland well. Refer to figure 8a for detailed description. 29

30 Figure 9a: Thermal maturation history for Ashcroft well in Devonian. X-axis represents the time in million years from Pennsylvanian to Permian. Y-axis represents temperature of the Devonian strata. Blue line indicates modeled thermal history created without any additional heat flow. Red line is hypothetical thermal history to achieve recorded %Ro. Difference in temperature is only 5ᵒC here. Heat flow needed to reach the recorded %Ro is about 130ᵒC Figure 9b: Thermal maturation history for Svetz well in Devonian. X-axis represents the time in million years from Pennsylvanian to Permian. Difference in temperature is about 80ᵒC here. Heat flow needed to reach the recorded %Ro is about 220ᵒC. Refer figure 9a for detailed description. 30

31 Figure 9c: Thermal maturation history for Westmoreland well in Devonian. X-axis represents the time in million years from Pennsylvanian to Permian. Difference in temperature is about 80ᵒC here. Heat flow needed to reach the recorded %Ro is about 220ᵒC. Difference in temperature and heat flow is similar to Svetz well. Refer figure 9a for detailed description Figure 10: Possible combination of fluid temperature and fluid velocity to achieve recorded %Ro of X-axis represents the fluid velocity in km/myr. Y-axis represents the fluid temperature in ᵒC. The combination can be either higher temperature with lower velocity or lower temperature with higher velocity.(tornegard, 2010) 31

32 Figure 11: Location of Rome Trough in Western Pennsylvania. Sets of normal faults and thrust faults are present here. Svetz well is in the region of the Rome Trough. Westmoreland well are close but not in the trough region. Ashcroft well is far from the Rome Trough. The Rome Trough is reactivated by Alleghanian Orogeny. (Kulander and Ryder, 2005) Figure 12: Heat transfer through vertical heat advection. X-axis is the depth that increases from top to bottom. Y-axis represents the temperature of the sedimentary layer that increases further to the right. The curve lines in the figure are the geothermal gradient. The geothermal gradient changes as heat brought from below increases. 32

33 Figure 13: Illustration of lateral fluid migration. To the right is the thrust sheet. To the left is the foreland basin. Deforming thrust sheet on the right due to mountain build up squeezes fluid from the thrust sheet to foreland basin. Oliver describes this as orogenic squeegee (Oliver, 1986). Figure 14: Heat transfer through lateral heat advection. X-axis is the depth that increases from top to bottom. Y-axis represents the temperature of the sedimentary layer that increases further to the right. The curve lines in the figure are the geothermal gradient. The geothermal gradient changes as heat from outside source increases. 33

34 Appendices Ashcroft Input for Backstrip model Input for SlugSed ************** sub : type of model, subsidence [sub] or sedimentation [sed] 10 : number of stress periods e6 0 : layer1 parameters: depth of node at SBI (m), basement conductivity (W/m- K), thermal capacity (J/m^3-K), porosity (decimal) e6 0 : layer2 parameters: depth of node at layer1/layer2 interface, basement conductivity (W/m-K), thermal capacity (J/m^3-K), porosity (decimal) 4.30e6 : parameter, thermal capacity of water (J/m^3-K) 2.65e6 : parameter, thermal capacity of sediment (J/m^3-K) 0.6 : parameter, thermal conductivity of water (W/m-K) 2.74 : parameter, thermal conductivity of sediment grains (W/m-K) 0.7 : parameter, surface sediment porosity (decimal) e : parameter, constants for porosity = f(z). A+Bz+Cz^2+Dz^3+Elnz+Fexp(G*Z)+H^(Iz) m : parameter, porosity = f(z) where z is in [m] or [km] 0.0 : parameter, minimum allowable sediment porosity (decimal) 0 0 : parameter, constants for permeability = f(phi) when pressure term is used to drive seepage: perm = Aexp(B*(porosity/(1-porosity))) 34

35 0.5 : parameter, scaling factor theta (for crank-nicholson solution: 0-1) 0=explicit, 1=implicit, 0.5=mixed 2 : parameter, calculate heat flow between surface and this node no : Flag, allow the removal of nodes from upper basement [yes/no] followed by maximum number of nodes to remove. Will remove a basement node when a sediment node is added yes : Flag, write output to a text Log file [yes/no] (Will write input-file data regardless) ************** 28.e : time, length of this stress period (in yrs) followed by maximum time step T : boundary condition paramaters for lower boundary: [T] or [q] = f(time in yrs): A+B(time)+C/sqrt(D*time) 0 : boundary condition (upper), temperature in degrees C that boundary is held : parameter, basement subsidence rate or sedimentation rate during this s : parameter, [s] seepage followed by value in m/yr or [p] lower boundary [] : filename containing constants for calculating production/sink (Q=f(t)) values : parameter, number of time steps to increment before storing data in Mat 52.e : time, length of this stress period (in yrs) followed by maximum time step T : boundary condition paramaters for lower boundary: [T] or [q] = f(time in yrs): A+B(time)+C/sqrt(D*time) 0 : boundary condition (upper), temperature in degrees C that boundary is held : parameter, basement subsidence rate or sedimentation rate during this s : parameter, [s] seepage followed by value in m/yr or [p] lower boundary [] : filename containing constants for calculating production/sink (Q=f(t)) values 35

36 : parameter, number of time steps to increment before storing data in Mat 45.e : time, length of this stress period (in yrs) followed by maximum time step T : boundary condition paramaters for lower boundary: [T] or [q] = f(time in yrs): A+B(time)+C/sqrt(D*time) 0 : boundary condition (upper), temperature in degrees C that boundary is held : parameter, basement subsidence rate or sedimentation rate during this s : parameter, [s] seepage followed by value in m/yr or [p] lower boundary [] : filename containing constants for calculating production/sink (Q=f(t)) values : parameter, number of time steps to increment before storing data in Mat 17.e : time, length of this stress period (in yrs) followed by maximum time step T : boundary condition paramaters for lower boundary: [T] or [q] = f(time in yrs): A+B(time)+C/sqrt(D*time) 0 : boundary condition (upper), temperature in degrees C that boundary is held : parameter, basement subsidence rate or sedimentation rate during this s : parameter, [s] seepage followed by value in m/yr or [p] lower boundary [] : filename containing constants for calculating production/sink (Q=f(t)) values : parameter, number of time steps to increment before storing data in Mat 57.e : time, length of this stress period (in yrs) followed by maximum time step 36

37 T : boundary condition paramaters for lower boundary: [T] or [q] = f(time in yrs): A+B(time)+C/sqrt(D*time) 0 : boundary condition (upper), temperature in degrees C that boundary is held : parameter, basement subsidence rate or sedimentation rate during this s : parameter, [s] seepage followed by value in m/yr or [p] lower boundary [] : filename containing constants for calculating production/sink (Q=f(t)) values : parameter, number of time steps to increment before storing data in Mat 11.e : time, length of this stress period (in yrs) followed by maximum time step T : boundary condition paramaters for lower boundary: [T] or [q] = f(time in yrs): A+B(time)+C/sqrt(D*time) 0 : boundary condition (upper), temperature in degrees C that boundary is held : parameter, basement subsidence rate or sedimentation rate during this s : parameter, [s] seepage followed by value in m/yr or [p] lower boundary [] : filename containing constants for calculating production/sink (Q=f(t)) values : parameter, number of time steps to increment before storing data in Mat 48.e : time, length of this stress period (in yrs) followed by maximum time step T : boundary condition paramaters for lower boundary: [T] or [q] = f(time in yrs): A+B(time)+C/sqrt(D*time) 37

38 0 : boundary condition (upper), temperature in degrees C that boundary is held : parameter, basement subsidence rate or sedimentation rate during this s : parameter, [s] seepage followed by value in m/yr or [p] lower boundary [] : filename containing constants for calculating production/sink (Q=f(t)) values : parameter, number of time steps to increment before storing data in Mat 12.e : time, length of this stress period (in yrs) followed by maximum time step T : boundary condition paramaters for lower boundary: [T] or [q] = f(time in yrs): A+B(time)+C/sqrt(D*time) 0 : boundary condition (upper), temperature in degrees C that boundary is held : parameter, basement subsidence rate or sedimentation rate during this s : parameter, [s] seepage followed by value in m/yr or [p] lower boundary [] : filename containing constants for calculating production/sink (Q=f(t)) values : parameter, number of time steps to increment before storing data in Mat 49.e : time, length of this stress period (in yrs) followed by maximum time step T : boundary condition paramaters for lower boundary: [T] or [q] = f(time in yrs): A+B(time)+C/sqrt(D*time) 0 : boundary condition (upper), temperature in degrees C that boundary is held : parameter, basement subsidence rate or sedimentation rate during this 38

39 s : parameter, [s] seepage followed by value in m/yr or [p] lower boundary [] : filename containing constants for calculating production/sink (Q=f(t)) values : parameter, number of time steps to increment before storing data in Mat 51.e : time, length of this stress period (in yrs) followed by maximum time step T : boundary condition paramaters for lower boundary: [T] or [q] = f(time in yrs): A+B(time)+C/sqrt(D*time) 0 : boundary condition (upper), temperature in degrees C that boundary is held : parameter, basement subsidence rate or sedimentation rate during this s : parameter, [s] seepage followed by value in m/yr or [p] lower boundary [] : filename containing constants for calculating production/sink (Q=f(t)) values : parameter, number of time steps to increment before storing data in Mat ************** 63 : node, number of nodes. Following are node depths (m), initial temps (deg C), radiogenic production/sink (W/m^2), [optional] conductivity (W/m-K) E E E E E E E E E E E E E

40 E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E

41 E E E+00 0 Svetz Input for Backstrip model Input for SlugSed ************** sub : type of model, subsidence [sub] or sedimentation [sed] 11 : number of stress periods e6 0 : layer1 parameters: depth of node at SBI (m), basement conductivity (W/m- K), thermal capacity (J/m^3-K), porosity (decimal) e6 0 : layer2 parameters: depth of node at layer1/layer2 interface, basement conductivity (W/m-K), thermal capacity (J/m^3-K), porosity (decimal) 4.30e6 : parameter, thermal capacity of water (J/m^3-K) 2.65e6 : parameter, thermal capacity of sediment (J/m^3-K) 0.6 : parameter, thermal conductivity of water (W/m-K) 2.74 : parameter, thermal conductivity of sediment grains (W/m-K) 0.7 : parameter, surface sediment porosity (decimal) e : parameter, constants for porosity = f(z). A+Bz+Cz^2+Dz^3+Elnz+Fexp(G*Z)+H^(Iz) 41