Regional
Tectonic Controls on Reservoir and Seal Quality of Mio-Pliocene Fluvial-Channel
Sandstones, Bohai Basin, Eastern China
Castellanos, Hugo A.1,
Paul Mann2 (1) The University of Texas at Austin, Austin, TX (2)
Jackson School of Geosciences, The University of Texas at Austin, Austin, TX
Subsidence analysis of 10 wells from the
200,000 km2 Bohai basin, eastern China; reveals an
acceleration of subsidence from rates of 13 m/my during
the Miocene to 53 m/my during the Pliocene. The zone of rapid subsidence occurs
in a 200-km-wide belt flanking the presently active, right-lateral Tan-Lu fault
zone that traverses the entire Bohai basin in a NNE
direction. The mechanism for rapid subsidence flanking the Tan-Lu fault can be
related to displacements along east-west-striking, secondary normal faults. We
describe the stratigraphic effects of this tectonic
event on non-marine, fluvial sedimentation using an integrated well log and
seismic data set. The Miocene and Pliocene fluvial sag deposits of the western
offshore portion of the Bohai basin have been
subdivided into ten regional correlatable
accommodation/supply cycles using well logs and seismic data. Fluvial-channel
sandstones of the Guantao Formation older than 5.1 my
laterally and/or vertically contact one another or are separated by a few feet
of floodplain facies suggesting deposition under
lower accommodation/supply conditions. Erosion usually preceded channel-fill
deposition therefore only the lowermost elements of channel successions were
typically preserved resulting in a high sand to mud ratio. Fluvial-channel
sandstones of the Pliocene Minghuazhen Formation
younger than 5.1 my are isolated and encased within
floodplain facies and show well developed splays
suggesting deposition under higher accommodation/supply conditions. Pre-5.1 my
sandstones form better oil reservoirs than the younger unit due to their
greater degree of continuity with adjacent sandstone bodies and the higher
degree of sorting of the fluvial sand itself.