TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIt is essential that precipitation of "asphaltenes" is recognised early in the planning stage of any EOR project so that appropriate testing can be performed to evaluate whether there will be a negative impact on reservoir performance. This paper presents detailed evaluations of extended compositional and PVT data which were obtained during extensive EOR tests using a light Middle East crude and CO 2 . The compositional measurements clearly confirm that "asphaltene" precipitation occurs during gas injection and that the properties of the heavy end fraction are significantly reduced.Before the C36+ data could be successfully interpreted, it had to be "calibrated" with data from a true boiling point distillation; this is explained. Detailed evaluations of the C36+ concentrations in the normalised C11+ fraction during swelling, equilibrium contact and forward multiple contact tests are presented.The changes in the C36+ concentrations result in changes in the physical properties of the plus fraction. It is essential that these changes are reflected in the fluid characterisation and tuning of the EOS. Also included are detailed predictions from various EOS models with and without taking into account the alteration in the physical properties of the C+ fraction.Because minimal tuning is performed, predictions from the EOS models should be reasonably precise. The paper includes preliminary predictions of EOR behaviour using different injection gas compositions.The paper concludes with recommendations for modifications to analytical programs for investigating gas injection processes which would lead to a better understanding of the fluid behaviour. Also included are suggestions for future research to better characterise the deposited "asphaltenes" which will hopefully result in more accurate predictions as to whether these precipitated asphaltenes will negatively impact reservoir performance.

No abstract