Interpretation of 3D multicomponent seismic data for investigating natural fractures in the Horn River Basin, northeast British Columbia

Abdallah A. Al-Zahrani

ABSTRACT

A 3D multicomponent seismic dataset from the Horn River Basin was assessed for mapping fractures. The data had good fold, offset and azimuth distributions and several approaches were used to interpret the distribution of natural fractures. In addition to amplitude mapping, PP and PS curvature maps enhanced the structural interpretation of the data and enabled the lateral continuity of faults and fractures to be mapped across the area of the seismic survey. Both horizon and volume based most negative curvature were effective in mapping fault and fracture trends within both Exshaw and Muskwa shale gas targets.

At the Exshaw level, the curvature shows one main fault trend: northwestsoutheast trending normal faults that dip toward the southwest. At the Muskwa level, the curvature image shows different major fault trends, namely north-south trending normal fault, northeast-southwest trending reverse fault, and northwest-southeast trending strikeslip fault. Fractures interpreted using curvature attributes are close to the major faults and their dominant trends are generally parallel to the major faults in the area.

The integration of curvature, interval Vp/Vs, scaled Poisson's ratio computed from the AVO analysis, instantaneous frequency and amplitude attributes yields an improved overall structural and rock properties interpretation. The most negative curvature map highlights the major fault and fracture trends and the Vp/Vs map, the instantaneous frequency map as well as the amplitude maps highlights potential highly fractured areas within the shale reservoir that have been induced by the major faults. The high spatial correlation of the scaled Poisson's ratio computed from the AVO analysis with interval Vp/Vs maps computed at the level of Exshaw and Muskwa reservoir suggest areas of possible increased reservoir potential from these maps. Areas of low interval Vp/Vs are interpreted to outline possible better porosity development within the Exshaw and Muskwa formations.

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