Integrated Microseismic and 3D Seismic Interpretation Integrated Microseismic and 3D Seismic Interpretation page 1

Integrated Microseismic and 3D Seismic Interpretation Integrated Microseismic and 3D Seismic Interpretation

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  • Integrated Microseismic and 3D Seismic Interpretation Thomas H. Wilson 1, Ariel K. Hart1, Pete Sullivan2, and Doug Patchen1,3

    1Department of Geology and Geography, West Virginia University, 2Energy Corporation of America, 3National Research Center for Coal and Energy

    Summary This research effort integrates microseismic data collected during hydraulic frac’ing operations conducted in a cluster of horizontal Marcellus wells in Greene County, PA with 3D seismic data over the area. Microseismic activity is displayed in the context of subsurface geology using well log and 3D seismic data. A key goal of these efforts will be to determine the relationship of microseismic activity to subtle faults and fracture systems extracted from the 3D seismic data.

    Objectives 1) Develop a 3D seismic interpretation of an active Marcellus shale gas development area; 2) Incorporate available geophysical logs and subsurface data into the geophysical characterization and subsurface interpretation; 3) Position microseismic events in the subsurface stratigraphic framework and 3D seismic interpretation; 4) Evaluate relationship between seismic scale fault networks, other seismic attributes and microseismic distribution; 5) Create a workflow you can use and modify for decision making on placement of future laterals.

    Overview (continued) High frequency attenuation is commonly observed in wave propagation through fracture zones and faults. We use t*attenuation to identify areas of high frequency loss across windowed regions throughout the 3D seismic volume. The 3D attenuation volume is then used as an input to a seismic discontinuity detection process (in this case, Ant Tracking). The discontinuities (10) fall into two roughly orthogonal trends (~N50E and ~N40W). The seismic scale faults have roughly N25E trend (11) that coincides with the trend of local surface anticlines (Washington and Hundred). The out-of-zone events are observed in an area where the discontinuities form a nearly-vertical fan-like cluster (8 and 9) on the northwest limb of the local drag fold. This is a somewhat unique feature of the area. In addition, we note that the Marcellus fold and fault in the treatment area die out through 1500’ of overlying strata, whereas fault offsets to the east appear to continue vertically upward through those overlying strata. Frequency magnitude plots for two prominent out-of-zone clusters (12A) yield three b-values. The larger and vertically more extensive East cluster (12B & C) is localized in the XY plane (12C). Event magnitudes less than -2 in the East cluster have b-value of 1.61. The general trend suggests that higher magnitude rupture might be more likely; however, the frequency of occurrence for the higher magnitude events drops off more steeply for M>-2, with b-value of ~4. The deeper West cluster has b-value of 5. The high b-value suggests larger magnitude events are very unlikely in this area. Events in the East cluster should be subdivided based on depth to see if the larger magnitude events are stratigraphically restricted. Fracture systems or mechanical heterogeneity in the shallower zone may be conducive to failure along larger-area surfaces.

    Status Significant progress toward key deliverables has been made since our May 1 startup. Development of the data base in an integrated workstation environment has been completed. Post-stack processing workflows were developed to help enhance subtle faults and possible fracture zones in the 3D seismic data set. Interpretation of those subtle features is underway along with evaluation of interrelationships between microseismic activity subtle faults and fracture systems. Our efforts have resulted in two abstract submissions noted below. No significant obstacles to continued progress have been encountered.

    Abstract Submissions Hart, A. K., Wilson, T. H., and Sullivan, P., submitted, 3D Seismic Attribute-Assisted Analysis of Microseismic Events within the Marcellus Shale: for presentation at the AAPG International Exhibition and Conference, Houston, TX, April, 2014. Wilson, T. H., Hart, A. K., and Sullivan, P., submitted, 3D Seismic Workflows Developed to Evaluate Out-of-Zone and Stealth-Zone Microseismic Behaviors: Marcellus Shale, Central Appalachians, USA: for presentation at the AAPG International Exhibition and Conference, Houston, TX, April, 2014.

    Acknowledgements This research is undertaken through the Houston Advanced Research Center Environmentally Friendly Drilling Program funded through the RPSEA. Schlumberger Petrel and IHS Kingdom Suite software were used to undertake much of the analysis. Appreciation is extended to the Energy Corporation of America for providing 3D seismic, microseismic and well data being evaluated in this research effort.

    Environmentally Friendly Drilling Systems 2013 Year-end Review

    Overview In this study we examine interrelationships between 3D seismic response and anomalous microseismic distribution observed during hydraulic fracture treatments from a cluster of Marcellus Shale wells in the Appalachian foreland area near the west margin of the Rome Trough. Type log response for the Marcellus in the study area was developed using a nearby sonic and gamma ray log (1). Log correlations of marker beds were carried through several wells in the area of 3D seismic coverage (2). A synthetic seismic tie (3) provided the basis for seismic interpretation. Checkshot locations did not consistently bound the shale section (4). Interval velocities computed from the checkshot data were anomalously high. A velocity function was developed independently from the integrated sonic following the seismic tie. Additional calibration was obtained by matching depth converted seismic surfaces to well top picks and geosteering reports from treatment wells associated with anomalous microseismic clusters (5, 6 and 7). Seismic data were enhanced for 3D visualization and seismic discontinuity extraction in the vicinity of the treatment area using time-variant trace amplitude slicing and differential attenuation (t*attenuation) computations. Amplitude slicing uses absolute values of trace amplitude followed by bandpass filtering in a series of two to three steps to increase apparent frequency content. The output retains direct relationship to variations in signal phase and frequency content through time. The process improves visualization and interpretation of subtle amplitude and phase variations related to local structural and stratigraphic features (8 and 9).

    3) Synthetic seismic tie 2) Log correlations: flattened on the top of the Marcellus

    Marcellus

    Onondaga

    1) Type log responses : sonic and γ-ray

    Marcellus

    4) Checkshot locations relative to stratigraphic markers 5) Depth converted seismic volume using velocity model derived from synthetic tie

    and well top picks

    6) Base of the shale/top of the Onondaga interpreted from depth-converted seismic.

    7) Microseismic events shown in depth relative to the base of the shale section

    8) Microseismic events shown on depth converted seismic display. Line cuts

    through microseismic cloud.

    9) Interpreted faults along seismic line through the out-of-zone microseismic cloud. Structures in the shale section overlying the

    Marcellus are not unique to the stimulated area.

    10) Seismic discontinuities and cluster locations 11) Seismic discontinuities on the Onondaga. Fault intersections are highlighted 12) Gutenberg-Richter frequency-magnitude plots for two prominent out-of-zone clusters.

    Magnitude ~Area 1/2

    -2.6 -2.4 -2.2 -2.0 -1.8

    Lo g

    N

    0.0

    0.5

    1.0

    1.5

    2.0

    2.5

    3.0 GR Plots

    East Cluster

    West Cluster

    b=5.04

    b=1.61

    b=3.98

    East (ft) -4500 -4000 -3500 -3000 -2500 -2000 -1500

    N or

    th (f

    t)

    0

    500

    1000

    1500

    2000

    2500 Out of zone microseismic clusters

    vertical cluster -5690 to -4860

    lower diffuse cluster -5690 to -5350

    West Cluster

    East Cluster

    Marcellus

    Onondaga

    B. C. A.

    ∆T (µsec/ft) 40 60 80 100 120

    D ep

    th (f

    ee t)

    7700

    7800

    7900

    8000

    8100

    8200

    8300

    8400

    Gribble Sonic

    γ ray 50 10

    0 15

    0 20

    0 25

    0 30

    0 35

    0 40

    0

    γ ray

    Burkett Tully

    Hamilton

    Upper Marcellus Cherry Valley

    Lower Marcellus

    Onondaga

    Huntersville

    Slide Number 1