Design of Laboratory Models for Study of Miscible Displacement

Abstract

Scaled laboratory-model studies provide a powerful method for evaluation of a proposed oil-recovery process. In recent years, models have been used extensively to evaluate processes in which solvents displace oil, both for general cases and for specific reservoir conditions. Since the performance of a miscible flood in a horizontal reservoir can be significantly affected by transverse mixing between solvent and oil, this displacement mechanism must be accurately simulated in the scaled model studies. Unfortunately, precise scaling of transverse dispersion coupled with the requirement of geometric similarity requires impractically large laboratory models and long times for experiments.If scaling requirements for miscible displacements could be relaxed while accurate simulation of essential displacement mechanisms is maintained, the utility of model studies would be greatly enhanced. The purpose of the work reported herein was to evaluate the relative importance of various mechanisms affecting miscible displacement and to ascertain whether the essential features of the displacement process can be simulated even though some scaling groups are not satisfied. These studies were performed with completely miscible systems in linear, horizontal models packed with unconsolidated media.From the experimental results, a set of relaxed scaling criteria was formulated which allows the requirements of geometric similarity and equality of the ratio of viscous to gravity forces to be omitted for specified conditions. The relaxed criteria are valid whether transverse mixing is by molecular diffusion or by convective dispersion.Correlations which permit prediction of vertical sweep efficiencies in linear, horizontal reservoirs were developed from the experimental data when transverse mixing is by molecular diffusion, These same correlations may be used when transverse mixing is by convective dispersion if an empirically defined, effective, transverse dispersion coefficient is used in the description of the mixing process. The effective transverse dispersion coefficient correlation essentially duplicates the dispersion coefficient correlation for equal-viscosity, equal-density fluid systems. Experimental values for the effective transverse dispersion coefficient can be measured readily. Introduction One of the most effective methods for evaluation of miscible-displacement oil-recovery processes is that of displacements in laboratory models scaled to simulate reservoir conditions. For these laboratory studies to be meaningful, however, the essential displacement mechanisms affecting reservoir performance must be accurately simulated.Since the performance of a miscible flood in horizontal reservoirs, or in dipping reservoirs at high rates, can be significantly affected by transverse mixing of solvent and oil, this mechanism must be considered in the design of laboratory experiments. Unfortunately, precise scaling of transverse dispersion coupled with the requirement of geometric similarity requires impracticality large laboratory models and long experiment times. This difficulty seriously limits the utility of laboratory model studies.Craig, et al, demonstrated that geometric similarity is not required when mixing is unimportant. Their experimental data indicate, for the cases studied, that the displacement is sufficiently characterized by scaling the ratio of viscous-to-gravitational forces. This work suggests that relaxation of the requirement of geometric similarity and, possibly, other criteria might also be permissible when mixing is important, provided suitable groups describing the mixing process are scaled.The purpose of the work reported here was to evaluate the relative importance of various mechanisms affecting miscible displacement and to ascertain whether the essential features of the displacement process can be simulated even though some scaling groups are not satisfied. SPEJ P. 28^

Dispersion measurement as a method of quantifying geologic characterization and defining reservoir heterogeneity. Final report

“…A beam current between 200 to 400 nA and an average dose of about 100 pC on target was used. The targets were prepared by anodizing pure tantalum metal foil at a constant applied voltage of 100 V and an initial current density of 10 mA/cm2 in 2 cc of the effluent fluid mixture for 10 minutes of oxidation time.…”

Effects of Physical Parameter Range on Dimensionless Variable Sensitivity in Water Flooding Reservoirs

“…π 20 , π 21 , π 22 and π 23 denote the respective ratios of the reference pressure of oil and water, the bottom pressure of the production well, and the initial pressure to the reservoir pressure difference. π 24 is the dimensionless capillary force function.…”

“…Moreover, it is often very hard or sometimes even impossible to keep all of them in the laboratory experiment identical to the field test. For example, the precise scaling of both transverse dispersion and geometry may impractically require a huge model and an extremely long time interval in tests [21]. At the same time, modeling the ratios of the capillary and the driving forces to the gravitational force can induce a considerably high permeability, which can scarcely be realized in laboratory [4].…”

Scale-up of miscible flood processes

“…401-7. In that simulation, the dispersion and longitudinal dispersion coefficients were set from the correlations of Pozzi and Blackwell (1963) as Dt = 0.15x103 cm2/s and DI = 3,6x 103 cm2/s. The finger growth mechanisms identified in the experiment were also seen in the simulations.…”