Experimental PVT data needed to develop EoS Model for EOR Projects
- Jawad Azeem Shaikh (Calsep A/S) | Pashupati Sah (Calsep A/S)
- Document ID
- Society of Petroleum Engineers
- SPE Enhanced Oil Recovery Conference, 19-21 July, Kuala Lumpur, Malaysia
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 4.1.5 Processing Equipment, 5.2.1 Phase Behavior and PVT Measurements, 5.2.2 Fluid Modeling, Equations of State, 5.2 Reservoir Fluid Dynamics, 5.5 Reservoir Simulation, 4.1.2 Separation and Treating, 5.4.2 Gas Injection Methods
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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.
A miscible drive develops after numerous (several thousands) contacts between gas and the in-situ reservoir fluid. Such contacts result in a multitude of phase transitions and the intermittent existence of widely varying oil-gas mixture compositions. Reservoir engineers carry out compositional reservoir simulations to somehow recreate such phase behavior in order to study its effect on the ultimate recoveries. Compositional simulators require EOS models tuned to data representing the individual miscible processes.
EOR PVT experiments need to provide data points that can ensure the validity of the EOS models for the particular gas-oil fluid interactions. While the validity of the EOS models depends on the quality of the experimental data, the PVT data itself will be valid if and only if the fluid samples are representative of the in-situ reservoir fluid and the injected gas respectively.
A variety of factors come into play during the fluid sampling process including, but not limited to, sampling locations, sample volumes and the specific applicability of the sampling method used.
Fluid samples taken to the PVT laboratory need to be validated prior to initiating the full experimental program to ensure the samples received are consistent with those sent out from the field and hence still representative.
Finally, the samples are analyzed for their compositions as well as for their behavior under various pressure and temperature conditions. In EOR PVT experiments, the sample fluid phase behavior is additionally studied post mixing with the proposed injection gas composition through a variety of tests as described in this paper.
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