Role of Compositional Grading in a CO2 Injection Project; A Case Study

In any comprehensive reservoir study the first step is an accurate assessment of the spatial distribution of the fluid components in both horizontal and vertical directions. Compositionalgrading, which refers to variation in fluidcomposition with depth, has been observed in many reservoirs. In most cases, the oil density andheavy components composition increase with depth while methane and other light components composition decrease with depth. Such acompositional grading can have a significant influence on various aspects of reservoir development. When considering gas injection, onemust be aware that compositional effects (such as the development of miscibility) change with depth. In this work one of the southwest Iranian oilreservoirs was selected. The reservoir under study was a low shrinkage undersaturated oil reservoir with the oil API gravity of 30. Two simulationmodels of CO2 injection for enhanced oil recovery (EOR) process were prepared, one with considering compositional grading, and the otherfor uniform fluid condition. Two models were compared and the effect of compositional grading on optimum injection rate and recovery factor wasstudied. Considering compositional grading results in a more realistic but more complex simulation model, and simulation run time would increase, but because of the drastic difference between the results of the two cases, it cannot be ignored.

Keywords:

compositional grading , enhanced oil recovery , carbon dioxide , optimization , field development , reservoir simulation