Interaction of Production Strategy with Stratigraphic and Sedimentologic Heterogeneity in Carbonate Reservoirs
Fitch, Peter; Jackson, Matthew D.; Hampson, Gary J.; John, Cedric M.
Previous studies have shown that geologic heterogeneity across all scales of observation can act individually, or in combination, to impact fluid flow in carbonate reservoirs during hydrocarbon production. However, few studies have examined how production strategy influences the interaction between heterogeneity and flow. We use flow simulation and experimental design techniques to investigate how production strategy influences the relative impact of stratigraphic and sedimentologic heterogeneities on recovery from carbonate reservoirs. Two waterflood production strategies are compared: (1) water injection using producer and injector wells completed over the whole reservoir interval, and (2) water injection into an underlying aquifer and producers completed in the upper reservoir interval. Three well placement schemes are investigated for each strategy: (1) single line drive with 4 km well spacing, (2) repeat line drive with 1 km well spacing, and (3) a 5 spot pattern with 500 m well spacing.
In the first production strategy, contrasts in environment-of-deposition (EOD) belt petrophysical properties, and stratigraphic heterogeneities that control the volume, geometry and lateral continuity of EOD belts, have the largest impact on recovery. Flow in this strategy is primarily horizontal (parallel to stratigraphy), and heterogeneities such as cemented hardground surfaces, fingering of depofacies within EOD belts, and bed-scale sedimentary structures within depofacies, have little impact. However, flow in the second production strategy is largely vertical, so the impact of these heterogeneities is more significant. Well placement does not affect the rank order of heterogeneity in the first strategy, but in the second strategy, decreased well spacing further promotes vertical flow, thus impacting the rank order of heterogeneity. Production with an unfavorable end-point mobility ratio yields lower hydrocarbon recovery, and changes the impact of heterogeneity slightly, but does not alter the rank order.
Our results demonstrate that production strategy affects the interaction of heterogeneity and flow in carbonate reservoirs. Thus, the results of studies that aim to quantify and rank the impact of heterogeneity on flow should be applied with caution. Further understanding of heterogeneity and flow has the potential to streamline the reservoir modeling process, by allowing the modeler to focus on those heterogeneities that are key in a given production context.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013