Modeling of point bar geology using a grid transformation scheme and geostatistics
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Point bars, the convex inner banks of meandering rivers, exhibit distinct heterogeneities. Modeling these heterogeneities is essential because of the presence of mud/silt layers in point bars impede the flow of fluids in processes strongly controlled by buoyancy or gravity such as the steam chamber rise during Steam-Assisted Gravity Drainage (SAGD). This thesis details the modeling of point bars using geological trends and well data to supplement geostatistical simulation. The modeling processes in this thesis capture the internal geometry of the accretion 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 in performing statistical simulation in rectangular coordinate while honoring the curvilinear geometry of the point bar. An entire point bar model contains a series of accreting curviplanar 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. The flow simulation model investigated the effect of mud drapes and fining heterogeneities on the development of steam chamber in SAGD recovery. The mud drapes impeded the steam chamber rise. The steam chambers were initially divided into pockets based on the flow barriers present. After 1 years of production, the steam chamber reaches the top of the reservoir but continued to be separated by the mud/silt barriers. Comparing to the homogeneous case, the point bar model exhibited lower oil recovery.