Compositional reservoir simulations for fields undergoing gas injection are dependent on an Equation-Of-State (EOS) model that will correctly simulate the reservoir fluid phase behavior independent of concentration of injection gas. Such an EOS model will require extensive Enhanced Oil Recovery (EOR) PVT Experiments. It is important at the start of an EOR PVT project to define what experiments need to be undertaken. Only then will it be possible to define the sample volume needed to carry out all the EOR PVT experiments. The reservoir type will determine whether the samples can be taken from bottom hole or from the separator. Fluid samples at atmospheric conditions also need to be taken to carry out Carbon Number (True Boiling Point) distillation test. Different samples will generally have to be comingled to avoid compositional variations between samples used for different experiments.
Gas injection is most efficient if the reservoir pressure is higher than the minimum miscibility pressure (MMP). Miscibility develops through a critical point and therefore in addition to routine PVT data it is also important to measure EOR PVT data that will provide information about MMP and near critical phase behavior. The MMP is measured in a Slim Tube test while a Solubility Swelling Experiment will give the Px-diagram including the critical conditions and composition. It is also recommended to perform the Equilibrium Contact Mix and Multi Contact Studies to measure properties inside the phase envelope at near critical conditions. These two experiments need to be carefully designed to ensure to get the most out of them in the EOS modeling work.
The paper will outline design of EOR experiments, details to be aware of when carrying out the experiments and key data to be matched by the final EOS model.