Sensitivity Study of Flow Unit Definition by Use of Reservoir Simulation

Abstract

Abstract The concept of flow units has been developed to integrate geological and petroleum engineering data. A flow unit is defined as a group of reservoir rocks with similar properties that affect fluid flow. Different methods can be applied for the definition of flow units and their corresponding petrophysical properties. The amount of information required by each method varies depending on the data and the tools available. This leads to different flow unit interpretation of the same reservoir. The objective of this study is to compare seven methods for flow unit definition to a known answer using numerical simulation to predict the flow performance of the reservoir. The data set corresponds to the research well CSM Strat Test #61, which is located near Dad, Wyoming, and belongs to the Lewis Shale of the Greater Green River Basin. Conventional and specialized well log information is available for the 1700-ft deep well, in addition to petrophysical measurements on approximately 170 selected core plug samples taken from 600 ft of core. The data for the well includes: gamma ray log, bulk density log, caliper, sonic log, compensated neutron log, nuclear magnetic resonance, air permeability (Klinkenberg-corrected), helium core porosity, minipermeameter readings, capillary pressure analysis, and neural network synthetic permeability. A simple simulation model is developed using the software ECLIPSE 100, Black Oil. Fluid properties, dimensions of the reservoir, grid size, pressure and production data are the same for all the runs. A waterflood of an oil-water system is simulated as a means of best observing how flow unit delineation affects the results. The results of the reservoir simulation indicate that predicting flow performance varies depending on the flow unit model used. The flow performance is a strong function of the average permeability, and therefore of the flow unit definition method used. Interpretation of flow units based on petrophysical properties, logs, and stratigraphy are routinely done for characterization of a reservoir. Unless numerical simulation is carried out to confirm the flow unit assignment, errors occur. The use of erroneous flow models leads to incorrect prediction of flow performance in the reservoir.