**Characteristics of discrete
and basin-centered parts of the Lower Silurian regional oil and gas accumulation,
Appalachian basin:
Preliminary results from a data set of 25 oil and gas fields**

Robert T. Ryder

**U.S. Geological Survey Open-File
Report 98-216**

*Any use of trade, product, and
firm names is for descriptive purposes only and does not imply endorsement by the U.S.
Government*

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**Contents**

|AbstractIntroductionAvailability of relevent oil and gas field dataComparison of selected oil and gas field characteristics
        Depth to production and hydrocarbon types
        Structural setting and natural fractures
        Trap types
        Reservoir porosity and permeability
        Reservoir water saturation and volume and
    composition of produced waters
        Segregation of gas and fluids in reservoirs
        Reservoir pressure and bottom-hole
    temperature
        Ultimate gas recovery per wellDiscussionConclusionsReferences CitedAppendices
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

**Illustrations**

|**Figure 1**.  Map of the northern part
    of the Appalachian basin province (067) showing oil and gas plays in the Lower Silurian
    "Clinton" sands, Medina Group sandstones, and Tuscarora Sandstone identified in
    the 1995 USGS National Oil and Gas Assessment.                                                                                     
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|**Figure 2**.  Map of the regional
    hydrocarbon accumulation in Lower Silurian sandstone reservoirs of the Appalachian basin,
    U.S. and Canada showing oil and gas fields used in the report.  Also shown is the
    approximate boundary between discrete and basin-centered parts of the accumulation.                                                 
|**Figure 3**.  Correlation chart of
    Niagaran Provincial Series rocks (Lower to lower Upper Silurian) in the area of the
    regional accumulation.                                                                                                                                                                                                          
|**Figure 4**.  Plot depth to production
    vs. hydrocarbon type for oil and gas fields.                                                                                                                                                                                                                                                                         
|**Figure 5**.  Map of the regional
    hydrocarbon accumulation in Lower Silurian sandstone reservoirs of the Appalachian basin
    showing oil and gas fields used in this report.  Also shown is the approximate updip
    limit of the basin-centered (deep basin) gas accumulation and adjoining water-block trap
    of Davis (1984) and Zagorski (1991).
|**Figure 6**.  Plot of reservoir porosity
    vs. reservoir permeability for oil and gas fields.                                                                                                                                                                                                                                                                 
|**Figure 7**.  Plot of reservoir water
    saturation vs. depth to production for oil and gas fields.  Also shown are the volume
    and salinity of produced waters.                                                                                                                                                                                           
|**Figure 8**.  Plot of reservoir pressure
    vs. depth to production for oil and gas fields.                                                                                                                                                                                                                                                                    
|**Figure 9**.  Plot of bottom-hole
    temperature vs. depth to production for oil and gas fields.                                                                                                                                                                                                                                                               
|**Figure 10**.  Probability plot of
    estimated ultimate recover (EUR) of gas per well in the Northeast Salem field.                                                                                                                                                                                                                                           
|**Figure 11**.  EUR per well
    distributions for discrete and basin-centered parts of the regional accumulation.                                                                                                                                                                                                                                               
|**Figure 12**.  Generalized model of
    origin and modification of the Clinton/Medina basin-centered gas accumulation and
    adjoining discrete and hybrid accumulations.                                                                                                                                                                                     
|**Figure 13**.  Map showing discrete,
    hybrid, and basin-centered parts of the Clinton/Medina/Tuscarora regional hydrocarbon
    accumulation.                                                                                                                                                                                                               

**Tables**

|**Table 1**.  Summary of oil and gas fields
    in Ohio, Pennsylvania, and New York that constitute the dat set in this report.                                  
|------------------------------------------------------------------------------------------------------------------------------------------------------------------
|**Table 2**.  Summary of local and regional
    structural elements imprinted on the north- to northeast-striking structural trend of the
    Appalachian basin.
|**Table 3**.  Summary of trap types.                                                                                                                              
|**Table 4**.  Summary of produced water.                                                                                                                          
|**Table 5**.  Summary of gas and oil EUR
    per well distributions.                                                                                             



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