Foam, a dispersion of gas in liquid, has been investigated as a tool for gas-mobility and conformance control in porous media for a variety of applications since the late 1950s. These applications include enhanced oil recovery, matrix-acidization treatments, gasleakage prevention, as well as contaminated-aquifer remediation. To understand the complex physics of foam in porous media and to implement foam processes in a more-controllable way, various foam-modeling techniques were developed in the past 3 decades.This paper reviews modeling approaches obtained from different publications for describing foam flow through porous media. Specifically, we tabulate models on the basis of their respective characteristics, including implicit-texture as well as mechanistic population-balance foam models. In various population-balance models, how foam texture is obtained and how gas mobility is altered as a function of foam texture, among other variables, are presented and compared. It is generally understood that both the gas relative permeability and viscosity vary in the reduction of gas mobility through foam generation in porous media. However, because the two parameters appear together in the Darcy equation, different approaches were taken to alter the mobility in the various models: only reduction of gas relative permeability, increasing of effective gas viscosity, or a combination of both. The applicability and limitations of each approach are discussed. How various foam-generation mechanisms play a role in the foam-generation function in mechanistic models is also discussed in this review, which is indispensable to reconcile the findings from different publications. In addition, other foam-modeling methods, such as the approaches that use fractional-flow theory and those that use percolation theory, are also reviewed in this work. Several challenges for foam modeling, including model selection and enhancement, fitting parameters to data, modeling oil effect on foam behavior, and scaling up of foam models, are also discussed at the end of this paper.

Wax removal by pigging is costly in sub-sea oil production. Cost-effective scheduling of pigging can be achieved based on the deposition rate predicted by wax deposition models. Conventional wax deposition models predict wax deposition rates on the basis of Newtonian fluid mechanics. Such an approach can become invalid for highly waxy crude oils with non-Newtonian rheology. In this investigation, different simulation techniques, including large eddy simulation, Reynolds-averaged Naiver–Stokes equations, and the law of the wall, were applied to model non-Newtonian pipe flow. It was discovered that the law of the wall method is the best method to calculate the velocity profile, shear stress and the turbulent momentum diffusivity in turbulent non-Newtonian pipe flow of waxy oil. An enhanced wax deposition model considering the non-Newtonian characteristics of waxy oil using the law of the wall method was developed and applied to predict wax deposition rates in a field-scale pipeline.

Wax deposition poses severe risks to crude oil production systems. In order to remediate wax deposition, pigging operation is performed routinely to scrape wax deposits from the pipe wall. Proper determination of the pigging frequency is crucial to estimating the operating costs associated with the pigging operations as well as the risks of pipeline blockage by wax deposit. In order to predict the wax deposition rate and the deposit thickness to be pigged, existing wax deposition models simulate the hydrodynamics, heat and mass transfer of oil pipe flows based on Newtonian fluid mechanics. However, when temperature of the oil drops below the wax appearance temperature (WAT), wax molecules precipitate to form a suspension of wax crystals in oil, resulting in non-Newtonian fluid characteristics. In order to generate more reliable wax deposition predictions, the methodology to model the hydrodynamics, heat and mass transfer as well as deposit growth considering the non-Newtonian fluid characteristics needs to be developed. In this study, we present an improvement of the existing university-developed wax prediction model1 by incorporating the non-Newtonian fluid characteristics of waxy crude oil described by the suspension of fractal aggregates (SoFA) model. This enhancement is first presented for laminar flow regime. This improved model is then applied to provide insights on 1) the impacts of non-Newtonian characteristics on the heat and mass transfer aspects of wax deposition, 2) the effect of shear on wax deposition and 3) the role of wax inhibitors on wax deposition.

Summary Oil recovery in heterogeneous carbonate reservoirs is typically inefficient because of the presence of high-permeability fracture networks and unfavorable capillary forces within the oil-wet matrix. Foam, as a mobility-control agent, has been proposed to mitigate the effect of reservoir heterogeneity by diverting injected fluids from the high-permeability fractured zones into the low-permeability unswept rock matrix, hence improving the sweep efficiency. This paper describes the use of a low-interfacial-tension (low-IFT) foaming formulation to improve oil recovery in highly heterogeneous/fractured oil-wet carbonate reservoirs. This formulation provides both mobility control and oil/water IFT reduction to overcome the unfavorable capillary forces preventing invading fluids from entering an oil-filled matrix. Thus, as expected, the combination of mobility control and low-IFT significantly improves oil recovery compared with either foam or surfactant flooding. A three-component surfactant formulation was tailored using phase-behavior tests with seawater and crude oil from a targeted reservoir. The optimized formulation simultaneously can generate IFT of 10−2 mN/m and strong foam in porous media when oil is present. Foam flooding was investigated in a representative fractured core system, in which a well-defined fracture was created by splitting the core lengthwise and precisely controlling the fracture aperture by applying a specific confining pressure. The foam-flooding experiments reveal that, in an oil-wet fractured Edward Brown dolomite, our low-IFT foaming formulation recovers approximately 72% original oil in place (OOIP), whereas waterflooding recovers only less than 2% OOIP; moreover, the residual oil saturation in the matrix was lowered by more than 20% compared with a foaming formulation lacking a low-IFT property. Coreflood results also indicate that the low-IFT foam diverts primarily the aqueous surfactant solution into the matrix because of (1) mobility reduction caused by foam in the fracture, (2) significantly lower capillary entry pressure for surfactant solution compared with gas, and (3) increasing the water relative permeability in the matrix by decreasing the residual oil. The selective diversion effect of this low-IFT foaming system effectively recovers the trapped oil, which cannot be recovered with single surfactant or high-IFT foaming formulations applied to highly heterogeneous or fractured reservoirs.

Modeling foam flow through porous media in the presence of oil is essential for various foam-assisted enhanced oil recovery (EOR) processes. We performed an in-depth literature review of foam-oil interactions and related foam modeling techniques, and demonstrated the feasibility of an improved bubble population-balance model in this paper. We reviewed both theoretical and experimental aspects of foam-oil interactions and identified the key parameters that control the stability of foam lamellae with oil in porous media. Upon reviewing existing modeling methods for foam flow in the presence of oil, we proposed a unified population-balance model that can simulate foam flow both with and without oil in standard finite-difference reservoir simulators. Steady-state foam apparent viscosity as a function of foam quality was used to evaluate the model performance and sensitivity at various oil saturations and fluid velocities. Our literature review suggests that, among various potential foam-oil interaction mechanisms, the pseudo-emulsion-film (gas/aqueous/oil asymmetric film) stability has a major impact on the foam-film stability when oil is present. Based on the pseudo-emulsion-film mechanism, we therefore developed a new foam-coalescence function in the population-balance model using the gas-water capillary pressure (Pcgw) in oil-free cases and the pseudo-emulsion capillary pressure (Pcpf) when oil was present. The respective critical values Pcgw * and Pcpf * can be estimated through disjoining pressure measurements. A smooth transition, from no foam destabilization at zero or substantially low oil saturations to no foam beyond a critical oil saturation, was considered for this purpose. The new model was able to handle the extent of the detrimental effect of oil on foam with one adjustable parameter k-2. This work consolidated various findings of foam-oil interactions based on pseudo-emulsion films in the past through a comprehensive literature survey. We have developed a unified model to simulate foam flow in porous media with and without oil using the mechanistic population-balance approach for the first time. This model can therefore be used in foam EOR simulations both in the oil-bearing zones as well as zones with no oil or residual oil present.