Liangmiao (Scott) Ye¹, Beverly A. Burns², Rick Levinson²
(1) ARCO EPT, Plano, TX
(2) ARCO Alaska, Anchorage, AK

Abstract: Scales of Heterogeneities in Braided Fluvial Reservoirs: A Case Study of the Tango Interval, Prudhoe Bay Field, North Slope of Alaska

The Triassic-age Tango reservoir in Prudhoe Bay Field is a braided fluvial deposit with subtle marine influences. In support of reservoir simulation studies, a detailed study integrating core, wireline log, seismic and outcrop analog data was undertaken to determine fieldwide vertical and lateral variations in reservoir properties of the Tango interval.

Sequence stratigraphic and sedimentological analyses conducted at the macroscopic scale delineated three major facies tracts occurring field-wide. Correlation of facies with core-derived petrophysical properties established seven modeling objects at the mesoscopic scale, which are characterized by distinctive lithologic and petrophysical properties and predictable spatial geometries and stacking patterns. Intra-channel baffles, such as inch-thick bar-drape shales, were identified as heterogeneity at microscopic scale. These analyses were used as the basis for reservoir zonation, determination of the lateral continuity of shales and mapping of lithofacies proportions and net:gross ratios across the field.

Spatial distribution of reservoir properties for numerical reservoir models also requires quantitative data about the geometries of the constituent lithofacies associations. This type of data were not obtainable from existing well or seismic control. Thus, it was necessary to obtain this critical data from appropriate outcrop analogues. A detailed compilation of braided fluvial lithofacies, from both in-house and published literature, provided this necessary data. The resulting comprehensive subsurface and analog databases provide the basis for both site-specific and field-wide reservoir simulation models. These databases are consistent with a regional geological model and our best understanding of the length scales of sand and shale body types associated with this reservoir.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana