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The Influence of Intra- and Inter-Channel Architecture in Selecting Optimal Gridding for Field-Scale Reservoir Simulation

Abstract

Sub-seismic scale heterogeneity in channelized deep water reservoirs can lead to significant uncertainty in reservoir connectivity and predicted performance. Though bed-scale heterogeneity can influence reservoir performance, reservoir simulation typically requires cell sizes much greater than the scale of internal channel architecture. Simple fine-scale sector modeling studies can be used to investigate the influence of bed-scale architecture and channel stacking on flow and connectivity and to identify optimal gridding and effective property modeling for field-scale volumetrics and flow simulation. Fine-scale simulations were performed using sector models developed from an outcrop analogue in the Tres Pasos Formation of the Magallanes Basin in Chilean Patagonia. These models represent a 550 m long segment of a single channel element, then two stacked channel elements. The influence of intra-channel architecture within a channel element was investigated using three different channel fills, each with an increasing level of detail: 1) single homogenous fill populated with average reservoir properties, 2) three depositional facies (axis, off-axis and margin) characterized by vertical boundaries and distinct average reservoir properties, and 3) distributed reservoir properties populated according to observed facies proportions, architecture, and trends. Reservoir performance testing was performed using a single injector-producer pair at a constant well spacing. The impact of well placement on reservoir performance was tested by systematically moving each well through a range of locations from the axis to margin of each channel. The influence of inter-channel architecture was investigated using stacked channel segments. The experiment above was repeated on the stacked segments by varying both internal channel fill and well placement. Variations in channel stacking were tested by changing the offset angle and distance between the two channel segments. End members of the stacked channel simulations were selected to identify an optimal cell size and effective properties for building coarse grid models. Primary conclusions include: 1) reduced detail in the representation of intra-channel architecture, including upscaling, tends to under-emphasize the critical role marginal facies play in inter-channel connectivity 2) error introduced by flow-averaged properties decreases as stacked channels become more vertically aligned.