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Asphaltene precipitation (AP) is recognized as a complicated occurrence that results in weakening reservoir characteristics and subsequent considerable decline in oil production rate. Asphaltene instability occurs due to variations in thermodynamic properties such pressure, temperature, and mixture composition. AP prediction is an important design factor in implementation of any enhanced oil recovery (EOR) process. In this study, experiments were conducted using some light oil samples to measure important phase behavior properties such as the bubble point pressure (BPP) and the amount of precipitated asphaltenes. A thermodynamics model was also developed to determine equilibrium compositions of the oil samples, considering AP. Then, potential application of a feed-forward artificial neural network (ANN) model, optimized by the imperialist competitive algorithm (ICA), was proposed to estimate BPP and the amount of AP. Comparison between the ICA-ANN predictions and the experimental data shows that the average absolute error between data originated from these two different approaches is less than 5%. In addition, it was found that temperature and pressure have the greatest impacts on AP during natural depletion. Employing laboratory PVT data, the thermodynamics framework resulted in construction of an asphaltene precipitation envelope. This study implies that utilization of an appropriate PVT model along with the ICA-ANN approach in the investigation of AP leads to more reliable predictions compared to the conventional ANN and also a scaling model. The outcomes of this study appear to be useful in the design stage of more-efficient EOR processes.

The impact of reservoir heterogeneities in terms of wettability at the macroscopic scale on the recovery efficiency of the gravity-assisted inert gas injection (GAIGI) process was investigated through a systematic experimental study for tertiary recovery of waterflood residual oil. Isolated inclusions of oil-wet consolidated glass beads were embedded in a continuum of unconsolidated water-wet glass beads to create heterogeneous packed columns. In comparison to water-wet homogeneous porous media, such heterogeneous media allowed us to establish higher waterflood residual oil saturation whose amount varied linearly with the volume fraction of oil-wet heterogeneities in the packing. Experimental results obtained from tertiary gravity drainage experiments demonstrated that the continuity of water-wet portions of the heterogeneous porous medium facilitates the tertiary oil recovery through the film flow mechanism, provided that the oil-spreading coefficient is positive. In addition, owing to the high waterflood residual oil content of the heterogeneous media tested, the oil bank formation occurred much earlier and grew faster, resulting in a higher oil recovery factor. However, having favorable wettability conditions in homogeneous porous media resulted in slightly lower reduced residual oil saturation after the GAIGI process compared to that in the heterogeneous media with the same condition of withdrawal rate. A relationship between the oil recovery factor at gas breakthrough and gravity number was developed for the heterogeneous and homogeneous media. The recovery factor at gas breakthrough versus gravity number in homogeneous media follows a similar trend as that of homogeneous water-wet porous media. However, at a given gravity number, the recovery factor of heterogeneous media was greater than that of the homogeneous media.

Naturally fractured reservoirs (NFRs) contain a significant amount of the world’s oil reserves. Oil recovery by gravity drainage in a NFR strongly depends on the capillary height of the porous medium. Capillarity and gravity forces are usually the major driving forces in NFRs. To address this issue, a series of flow visualization experiments were performed using unconsolidated packed models of rectangular geometry with two fractures on the side. Parametric sensitivity analyses were performed considering effects of different system parameters such as fracture aperture, matrix height and permeability, and fluid viscosity on liquid drainage rate. These experiments enabled us to capture some aspects of the flow communication between matrix block and fracture during gravity drainage. Results from this study showed that the rate of liquid flowing from matrix to fracture is proportional to the difference of liquid levels in the matrix and in the fracture (Hf– Hm). In addition, the characteristic rate and the maximum liquid drainage rate from these fractured models are determined for stable gravity-dominated processes. Also, it was concluded that the characteristic rate depends only on the dimensions of the fracture and properties of the test fluid, and not on the properties of the matrix. For a given fracture–matrix system with different initial liquid saturation conditions, it is observed that the production history can be correlated by plotting the fraction of recoverable liquid as a function of time. Furthermore, ultimate recovery factor and capillary threshold height can be correlated using dimensionless numbers such as the Bond number and the porosity ratio.

Growth of a new phase is experienced in several chemical engineering processes/operations such as polymer foaming, oil/gas transportation, bubbly columns, distillation towers, and petroleum recovery. Thus, it seems vital to understand the dynamics of transport phenomena and new phase (e.g., bubbles) evolution over the corresponding processes to efficiently design and operate the plant equipment. The present study introduces new analytical and approximate solutions for the growth of a new phase in a medium of finite extent. The governing conservation equations are solved by an effective mathematical approach through combination of variables and enhanced homotopy perturbation method (EHPM) where it is assumed that the mass transfer controls the rate of growth through both convection and diffusion mechanisms. The modeling outcome confirms the importance of the convection mass transfer in growth of the new phase in finite extent. The results show that the radius of the new phase is strongly dependent on the diffusivity, temperature, and initial void fraction. It is also found that the bubble evolution follows the power-law model. To examine the practical effectiveness of the developed mathematical models, the growth of water bubbles, hydrate particles (as a new phase), and bubbles (or gas) growth in oil reservoirs are studied. The models’ results are compared with some experimental data, exhibiting a very good agreement (e.g., error percentage of <5%). This research work offers systematic strategies for investigation of bubble expansion/shrinkage phenomena where the bubble growth dynamics are observed in various processes/systems.