An Integrated Approach of Reservoir Prediction in a Structurally and Stratigraphically Complex Area — A Miocene Example from Eastern Deepwater Gulf of Mexico

Wu, Xinxia; Mornet, Christopher; McGilvery, Mac; Blackerby, Jim

Reservoir prediction is a key factor in evaluating exploration risk in the deepwater Gulf of Mexico (DWGOM), where both structure and stratigraphy are very complex. In the eastern DWGOM, we applied an integrated approach to understand Miocene reservoir presence, distribution, thickness, continuity, etc., and to assess potential prospect /field economics. A predictive sand thickness map and a detailed depositional facies map were constructed subregionally for the Miocene to reflect our confidence of reservoir presence, quantity and connectivity. The map construction followed a few key steps. Step 1: regional understanding of the depositional and structural setting to provide context for subregional mapping. The eastern DWGOM was dominated by an extensive sand-rich turbidite and submarine fan complex at the toe of a dip-elongate sediment dispersal system during early Miocene time. That system was mainly supplied by a broad, progradational shelf margin delta and linked gravitational down-slope transport system from north-northwest. It deflected around and between salt structures, and ultimately deposited in the salt-modified paleo-toe of slope minibasins in the eastern DWGOM. Step 2: calculation of net sand thickness and net/gross ratio for available wells in the subregion. Step 3: subregional correlation, interpretation and mapping of key surfaces from 3-D (or 2-D) seismic data to construct isochore /gross interval thickness map, which was further used to identify paleo-depocenters and extract structure framework to confine minibasins. Step 4: calibration of seismic with well data and Identification sand-rich seismic facies. Step 5: calculation/estimation of sand thickness with a simplified equation: estimated sand thickness = calibrated sand-rich seismic interval thickness X net/gross ratio of correlative interval in nearby correlative wells. Here, "correlative" means similar depositional and structural setting. Step 6: integration of net sand from wells, estimated sand thickness from seismic, log and seismic facies interpretation, as well as regional knowledge to construct a final predictive sand thickness map and a detailed depositional facies map.

The Miocene reservoir distribution in the eastern DWGOM was controlled by both salt tectonics and the locus of sediment input. Thick sand commonly accumulated along the axes of a sandy depositional fairway (on-axis) and in paleo-bathymetric lows within minibasins (high accommodation). Thin sand often times is associated with off-axes deposition along the margins of the sand fairways, paleo-bathymetric highs (low accommodation), or complication of mass transport deposits. The sand-rich turbidite and submarine fan complexes are characterized by sheet turbidite complexes (both layered and amalgamated), distributary channels, and imbricated mass transport complexes.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013