Abstract

The Yufutsu oil and gas field, located in Hokkaido, northern Japan, produces hydrocarbon from a typical fracture-type reservoir composed of very tight Cretaceous granitic basement and overlying conglomerate of the Eocene. Here, delineations of faults accompanying large open fractures are essential for optimal developments.

To capture fault distribution objectively, various seismic-attribute estimates ascribed to fault distributions are derived from three-dimensional seismic data by computational procedures. However, to use the estimates properly, calibrating them with independent observations other than seismic data is important. We present a calibration scheme by coupling seismic data with microseismic data and in-situ stress data to delineate active faults under a strike-slip faulting stress regime in the Yufutsu field. Active faults are interpreted to be fluid pathways formed by shear dilation. In the calibration, two kinds of parameter sets are tuned. One controls linkages of fault responses fragmented by artificial noises caused by seismic acquisition and processing to adjust spatial continuities of fault surfaces properly. Another limits extracted fault strikes with respect to Mohr-Coulomb failure criterion to highlight active faults. The calibrated seismic-attribute estimates show a qualitative consistency with the microseismic hypocenter distribution observed during a massive hydraulic stimulation. In addition, a large difference in gas productivity observed at four wells, from very high productivity to no gas flowing, is clearly related to an existence of distinct lineation with strong magnitudes of the calibrated seismic attributes. It suggests that the calibrated estimate becomes a criterion to judge an economic viability of a well.

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