coherence

Coherence in 3D seismic interpretation is a volumetric attribute that quantifies the lateral similarity of waveforms between adjacent seismic traces over a short vertical analysis window, producing a normalized measure (0 to 1, where 1 indicates identical waveforms and 0 indicates no similarity) that images geological discontinuities where seismic reflection continuity breaks down across faults, fractures, channel edges, karst collapse, and stratigraphic boundaries; coherence is computed from the 3D seismic cube using one of three algorithms: cross-correlation coherence (C1, normalized cross-correlation between trace pairs), semblance-based coherence (C2, ratio of stacked-trace energy to total individual-trace energy, more robust to amplitude variation), and eigenstructure coherence (C3, dominant eigenvalue of the multi-trace covariance matrix normalized to total energy, least sensitive to noise and dip estimation errors). In Western Canada Sedimentary Basin 3D seismic interpretation, coherence volumes are standard deliverables particularly valuable in three geological contexts: mapping fault patterns in WCSB Devonian reef plays (Nisku, Leduc, and Cooking Lake formations) where fault-bounded reef structures and karst dissolution features appear as linear and circular coherence lows on time slices and horizon maps delineating trap geometry; imaging Cretaceous channel systems (Mannville Group, Viking Formation, Cardium Formation) where channel margins and facies boundaries appear as coherence lows guiding horizontal well steering for maximum pay intersection; and detecting natural fracture corridors in WCSB Montney, Duvernay, and Muskwa unconventional plays where lineament density and orientation from coherence volumes guides staging selection and horizontal well orientation for maximum fracture intersection. Coherence attribute extraction in WCSB 3D seismic interpretation workflows uses Petrel (Schlumberger/SLB), Kingdom (IHS Markit), and Paradigm GOCAD as the primary interpretation platforms, with coherence computed using a vertical analysis window of 8 to 24 milliseconds (two to six times the dominant seismic period at WCSB target depths of 1,000 to 4,000 m) and a multi-trace aperture of 3x3 to 7x7 traces in the inline-crossline grid.

• Coherence algorithm evolution and selection for WCSB 3D seismic structural interpretation: The three generations of coherence algorithms differ in computational cost and sensitivity to noise, dip errors, and amplitude variations: C1 cross-correlation algorithms require the analyst to correctly estimate the dip of the reflector before computing coherence (dip-guided coherence), making them sensitive to dip estimation errors in steeply dipping WCSB Foothills seismic where structural dips exceed 30 to 60 degrees and the dip estimation window must be large enough to capture the dipping reflection but small enough to avoid averaging across adjacent structural blocks; C2 semblance algorithms are computed without explicit dip estimation (multi-trace semblance over a flat window) and are the most computationally efficient, widely used in WCSB basin-scale interpretation where structural dips are gentle (less than 5 to 10 degrees in the Alberta Plains) and semblance provides adequate fault resolution; C3 eigenstructure algorithms provide the best noise rejection and sensitivity to subtle discontinuities but require substantial computation, making them practical only on workstation-class hardware at WCSB 3D survey sizes of 500 to 5,000 km2 that became standard in the 2010s as computer memory and processing speed increased. WCSB exploration and development teams typically compute all three coherence volumes and select the one providing the clearest image of target discontinuities for the specific geological problem (C1 for steep Foothills structures, C2 for Plains fault mapping, C3 for unconventional fracture characterization).
• Coherence-based fault mapping in WCSB Devonian carbonate reef plays: Devonian carbonate reef complexes in the WCSB (Nisku Formation reefs in the Brazeau, Pembina, and West Pembina fields; Leduc Formation reefs in the Redwater, Bonnie Glen, and Homeglen-Rimbey trend; Cooking Lake platform carbonates across central Alberta) are bounded by faults and surrounded by basinal shales that create high-amplitude impedance contrasts on the reef flanks; coherence volumes from WCSB 3D surveys over Devonian reef plays image the reef boundary as a continuous coherence low encircling the high-coherence reef interior, and distinguish fault-controlled reef terminations (linear coherence anomalies cutting across the reef trend) from dissolution-controlled karst (circular to irregular coherence lows within the reef body corresponding to void-fill breccia zones). In the Leduc reef play at Redwater (the largest oil field discovered in Alberta, 65,000 hectares, producing since 1948), 3D seismic coherence volumes acquired in the 1990s and 2000s refined the structural model of reef geometry and internal collapse features that controlled remaining oil distribution, enabling infill drilling programs to target high-coherence interior zones (highest porosity, lowest fracture intensity) and bypass low-coherence breccia zones (highest fracture density but also highest water influx risk in the mature waterflood).
• Coherence for stratigraphic channel and valley imaging in WCSB Cretaceous sandstone plays: WCSB Cretaceous incised valley fill systems in the Mannville Group (McMurray, Clearwater, and Grand Rapids formations) are the most prolific conventional heavy oil and in-situ bitumen reservoirs in the basin, and their mapping using coherence attributes extracted along interpreted horizon surfaces (horizon-extracted coherence maps, or co-rendered amplitude and coherence maps) provides information on channel width, sinuosity, lateral migration, and the position of inner channel bars (highest porosity) and muddy channel margins (coherence lows) that governs horizontal well placement in WCSB thermal CSS and SAGD programs. Viking Formation fluvial and deltaic sandstone channels in the Pembina and Swan Hills areas are interpreted from WCSB coherence volumes as meandering ribbon anomalies on shallow horizon extractions (400 to 900 m depth, high signal-to-noise ratio seismic), with channel widths of 200 to 800 m and sinuosity indices of 1.2 to 2.0 that define the productive reservoir geometry; coherence-guided Viking horizontal wells at Pembina field (Canadian Natural Resources, Husky Oil) have used coherence maps to steer wellbores along channel axes for 800 to 1,200 m horizontal sections within the productive sandstone, reducing dry hole rates from 25 percent to less than 8 percent compared to vertically drilled wells guided by amplitude maps alone.
• Coherence lineament analysis for natural fracture characterization in WCSB unconventional plays: In WCSB Montney, Duvernay, and Muskwa-Otter Park shale and siltstone plays, natural fracture corridors (opening-mode fracture swarms at 50 to 500 m spacing, oriented parallel to the maximum horizontal stress direction, NE-SW across most of the WCSB) appear as linear coherence lows in 3D seismic volumes because the fractured zone has a different elastic impedance (lower than the intact matrix) and a different reflection character (lower amplitude, more chaotic waveform) than the surrounding unfractured formation. Coherence lineament extraction in WCSB Duvernay shale interpretation (Kaybob, Edson, and Fox Creek areas of west-central Alberta) uses rose diagram analysis of lineament orientation to confirm the NE-SW Montney fracture trend, with deviations from this trend indicating stress-field rotation near major normal faults (Peace River Arch, Athabasca fault corridor) that influences hydraulic fracture propagation direction in horizontal wells; Duvernay wells drilled perpendicular to coherence lineaments (east-west horizontal) show 30 to 50 percent higher 12-month cumulative production compared to wells parallel to lineaments (north-south horizontal), validating the coherence-based fracture orientation model for well trajectory selection.
• Coherence attribute integration with other seismic attributes in WCSB multi-attribute interpretation: Coherence is most powerful when combined with complementary seismic attributes in multi-attribute displays: co-rendering coherence with amplitude (where coherence images discontinuities and amplitude images lithology/fluid contrasts) on the same horizon allows WCSB interpreters to distinguish faults (low coherence, amplitude discontinuity) from stratigraphic pinch-outs (low coherence, amplitude taper without offset), from diagenetic boundaries (coherence-continuous but amplitude-variable in WCSB carbonate dolomitization fronts); combining coherence with curvature (which measures the shape of the reflector surface) enhances lineament detection because natural fracture corridors produce both a coherence low (from impedance contrast) and a curvature anomaly (from the mechanical compaction differential across the fracture zone). WCSB machine learning seismic interpretation workflows (applied at Suncor, Cenovus, and ConocoPhillips in WCSB Montney and Duvernay programs) use coherence as one of 10 to 30 input attributes in neural network facies classification schemes that map reservoir quality and completion efficiency directly from 3D seismic, with coherence contributing to the identification of natural fracture density variations that dominate completion performance in WCSB tight reservoir plays.

Coherence Imaging Guiding WCSB Duvernay Horizontal Well Placement

A WCSB Duvernay shale operator in the Kaybob area of west-central Alberta used coherence volumes from a 340 km2 3D seismic survey to guide the trajectory selection for a 6-well horizontal drilling program targeting the Upper Duvernay condensate-rich interval at 3,400 m depth. C3 eigenstructure coherence was computed using a 16 ms window and 5x5 trace aperture. Lineament extraction from the coherence volume identified three dominant NE-SW trending fracture corridors at 400 to 600 m spacing, with coherence values of 0.55 to 0.70 within the corridors versus 0.90 to 0.95 in the intact matrix. Four wells were oriented east-west (perpendicular to the NE-SW fracture corridors) to maximize fracture intersection, while two offset wells drilled north-south (parallel to corridors) served as natural experiments. After 12 months, east-west wells averaged 2,450 m3 condensate equivalent per well versus 1,380 m3 for north-south wells, a 78 percent production difference consistent with the fracture intersection model. The 3D coherence lineament map was also used to identify a 2 km section of high-coherence, apparently unfractured rock in the central part of the survey that was avoided in well planning; post-drilling microseismic from the nearest well confirmed hydraulic fractures did not propagate into the high-coherence zone, validating the coherence-based geomechanical model.

Related Terms

Seismic attribute is the broader category; coherence is the most widely used discontinuity attribute in WCSB 3D interpretation, complementing amplitude, curvature, and impedance in multi-attribute structural and stratigraphic workflows. Coherence filtering uses the local dip field from coherence analysis to orient noise-suppression filters along reflector surfaces, preserving fault discontinuities while enhancing continuous reflections in WCSB 3D volumes. Fault detection is the primary coherence application in WCSB seismic interpretation; faults appear as linear lows on time slices and horizon extractions, enabling automated fault extraction across hundreds of km2. Fracture corridor characterization in WCSB Montney and Duvernay uses coherence lineament density and orientation to guide horizontal well trajectories; fracture-parallel wells produce 30-50% less than fracture-perpendicular wells. Seismic interpretation in WCSB 3D programs uses coherence in Petrel, Kingdom, and GOCAD, co-rendered with amplitude and curvature to distinguish faults, channels, and diagenetic boundaries.