Modeling point bars using a grid transformation scheme

Point bars, formed from meandering rivers, exhibit distinct heterogeneities. Modeling these heterogeneities is essential because of the presence of mud/silt layers that impede steam chamber rise in Steam-Assisted Gravity Drainage (SAGD). Previous point-bar models rely heavily on outcrops for geology. Such models may have difficulty extending to subsurface reservoirs where geological data is minimal. This paper details the modeling of point bars using geological trends and well data to supplement geostatistical simulation. The modeling processes in this paper capture the internal geometry of the accretions layers as well as geological trends. Curvilinear grids are constructed between major erosional surfaces where a grid transformation scheme is used to transform the curvilinear coordinates into orthogonal coordinates for geostatistical simulation. The grid transformation allows flexibility of performing statistical simulation in rectangular coordinates while honoring the curvilinear geometry of the point bar. An entire point bar model contains a series of accreting curvilinear grids. Geological modeling is done independently for each grid. The geology captures key trends that make up the heterogeneities in the model. The point bar model created is based on a modern point bar in the Brazos River. Data from thirty-three wells are used in creating the reservoir model. Several distinct trends are observed. There is an upward decrease in sediment size in the point bar. An overall fining downstream trend is observed in the vertical slices of the point bar. Heterolithic bedding is observed where frequent layers of silt extend from the top to near the base analogous to outcrops. Mud and silt dominate the upward regions of the point bar while conglomerate and cobble are mainly present at the base. This paper presents a reservoir modeling process that properly define point bar geology using only well data and geological trends. Without reliance on outcrops, modeling of point bars can be applied to subsurface reservoirs. A detailed geologic model provides greater insight to the heterogeneities seen in point bar reservoirs. Well defined heterogeneities in point bar models is critical to any SAGD simulation.