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Musial, Geoffray, Richard Labourdette, Jessica Franco, and Jean-Yves Reynaud,
Modeling of a Tide-influenced Point-bar Heterogeneity Distribution and Impacts on Steam-assisted Gravity Drainage Production: Example from Steepbank River, McMurray Formation, Canada
Geoffray Musial,1 Richard Labourdette,2 Jessica Franco,3 Jean-Yves Reynaud4
1BEICIP-FRANLAB 232 Ave. Napoléon Bonaparte, 92500 Rueil-Malmaison, France (e-mail: [email protected]); Previous address: Institut des Sciences de la Terre, Université Pierre et Marie Curie, Unité Mixte de Recherche Centre National de la Recherche Scientifique, 4 Place Jussieu, 75005 Paris, France.
2Total, Geosciences Technologies, Ave. Larribau 64018 Pau Cedex, France (e-mail: [email protected])
3Total, Geosciences Technologies, Ave. Larribau 64018 Pau Cedex, France (e-mail: [email protected])
4Université de Lille 1, UFR de Sciences de la Terre, Cité Scientifique-Bat. SN5, F-59655 Villeneuva d' Asca Cedex, France (e-mail: [email protected]); Previous address: Muséum National d'Histoire Naturelle, Département Histoire de la Terre, Bâtiment de Géologie-CP 48 43, rue Buffon F-75005 Paris, France.
The authors thank Total EP Canada for their technical assistance in this study. Thanks are extended particularly to all Total field workers who offered their support: Patrice Imbert, Fernand Segura, Rebecca Haspel, Alexis Licht, Olivier Parize, Remy Karle, and Remi Rateau.
Outcrops and subsurface investigations emphasize that the main bitumen reservoirs of the McMurray Formation are large point-bar deposits. Sedimentological studies performed on these reservoir objects have shown that tidal currents occurred in the meandering paleoriver system. These tidal inputs increased reservoir heterogeneities primarily because of successive mud decantation periods and the many reactivation or erosion surfaces.
Five main reservoir heterogeneities have been described on Steepbank River outcrops: mud accumulation during channel abandonment, mud drapes along accretion surfaces that are downward interfingered into cleaner sands, flood-plain deposits on top of the point bar, reactivation surfaces typically associated with mud-clast deposits, and mud-clast breccias accumulated at the base of the channel. At the same time, five main facies have been emphasized on these studied tide-influenced point bars: mud-clast breccias, cross-stratified sands, slightly heterolithic rippled sands, highly heterolithic burrowed sands, and thick mudstones. For each of these facies, petrophysical properties have been established, enabling their application as rock types for the Steepbank River outcrop modeling. This deterministic method of modeling, improved by light detection and ranging (LiDAR) data, used truncated Gaussian simulations constrained by the proportion cube, sedimentological logs corresponding to hard data, and adequate variograms. The resulting facies and heterogeneity distributions conform closely to the outcrop reality, lending support for the modeling method.
This deterministic sedimentological model is at the root of steam-assisted gravity drainage (SAGD) simulation tests performed for a water-steam injector horizontal well underlain by a fluidized-bitumen horizontal producer well. Results of the simulation boxes filled by this sedimentological modeling more closely match outcrop analogs than results obtained by the more commonly used purely stochastic models. This is caused by the occurrence of large-scale inclined heterolithic stratification (IHS), which is generally overlooked in stochastic models, or alternatively is replaced by horizontal heterogeneities, which would be highly detrimental for bitumen production from SAGD horizontal wells. Thus, in purely stochastic modeling, bitumen recovery prospects tend to be underestimated, or permeability heterogeneity is overestimated.
Finally, a comparison was made between SAGD simulation tests performed in the direction of point-bar lateral accretion versus tests performed parallel to the paleoriver flow direction. The comparisons show stronger bitumen recovery for the SAGD simulation tests performed parallel to the paleoriver thalweg. In this case, parallel to paleoriver flow direction, a better conformance of the steam chamber along the trajectory of the horizontal injector well is observed; and the steam chamber rises more slowly toward the ground surface. This is because in the SAGD simulation tests performed in the direction of point-bar lateral accretion, major reservoir heterogeneities exist as thin low-permeability mud beds within the large, low-angle, IHS. Such mud bed reservoir heterogeneities are less prevalent, and less restrictive, in the direction parallel to the paleoriver flow.
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