Stochastic and upscaled analytical modeling of fines migration in porous media induced by low-salinity water injection

Fines migration induced by injection of low-salinity water(LSW) into porous media can lead to severe pore plugging and consequent permeability reduction. The deepbed filtration(DBF) theory is used to model the aforementioned phenomenon, which allows us to predict the effluent concentration history and the distribution profile of entrapped particles. However, the previous models fail to consider the movement of the waterflood front. In this study, we derive a stochastic model for fines migration during LSW flooding, in which the Rankine-Hugoniot condition is used to calculate the concentration of detached particles behind and ahead of the moving water front. A downscaling procedure is developed to determine the evolution of pore-size distribution from the exact solution of a large-scale equation system. To validate the proposed model,the obtained exact solutions are used to treat the laboratory data of LSW flooding in artificial soil-packed columns. The tuning results show that the proposed model yields a considerably higher value of the coefficient of determination, compared with the previous models, indicating that the new model can successfully capture the effect of the moving water front on fines migration and precisely match the effluent history of the detached particles.

Hydro-mechanical analysis of rainfall-induced fines migration process within unsaturated soils

Seepage-induced fines migration under rainfall infiltration is a main cause leading to shallow failures in loose colluvial slopes. To describe the full process of fines migration within unsaturated soils during rainfall infiltration and the associated hydromechanical behaviors, a seepage-erosion-deformation coupled formulation is proposed in this paper. The governing equations proposed are implemented into a finite element code and used to investigate the influences of skeleton deformation on the rainfall infiltration process through unsaturated soil columns.The numerical results were presented in detail for a better understanding of the rainfall-induced fines migration process within unsaturated soils. Further,the obtained results are integrated into an infinite slope model for slope stability analysis. The results show that, the skeleton deformation will affect the rainfall infiltration rate and hence the timing of slope failures; meanwhile their influences are more evident if the fines deposition process is taken into account.Moreover, the slope stability could be reduced gradually due to the soil strength loss along with loss of fine particles. Therefore, particular attentions should be paid to analyzing the stability of soil slopes susceptible to internal erosion.

Two-dimensional finite element modeling of seepage-erosion coupled process within unsaturated soil slopes

Fines migration along with rainfall infiltration is a possible cause of failures of slopes composed of loose deposits.To investigate the intrinsic mechanisms,a rigid mathematical model which can fully capture the multi-phasic and multiphysical process is necessary.In this research,the macro and micro physical phenomena of fines migration process within deposited soil slopes under rainfall infiltration were summarized.Based on the mixture theory,a seepage-erosion model for unsaturated erodible soils capable to capture these phenomena mathematically was built based on a rigid theoretical framework.The model was used to simulate a set of rainfall flume tests involving fines migration phenomena with the finite element method.Two distinct slope failure modes observed experimentally,which were induced by the soil erosion-deposition properties,can be well reproduced by our numerical model.The seepage-erosion coupled process during the rainfall infiltration,as well as the intrinsic mechanism responsible for the slope failures,was illustrated in detail based on the numerical results.It was shown that the fines migration process can affect the hydro-mechanical response within unsaturated slopes significantly,and therefore special attention should be paid to those soil slopes susceptible to internal erosion.

Using nanotechnology to prevent fines migration while production

Formation damage due to fines migration is a major reason for well productivity decline for oil and gas wells.Formation fines are small enough to pass through pore throats causing pore plugging and permeability decline.Different factors affect fines migration such as flow rate,salinity,pH value,reservoir temperature and oil polarity,as well as changes in chemical environment induced by Enhanced Oil Recovery(EOR)agents.This paper focuses on the effect of flow rates on fines detachment from the grain surfaces,which causing permeability reduction.As the fluid inside the reservoir moves towards the wellbore,the fluid velocity increases,when the fluid reaches the critical flow rate these fines can be picked up into the fluid.These fines captured by thinner pore throats causing pore plugging and permeability reduction.Different concentrations of nanoparticles were used to fix these fines on their sources and prevent their mobilization at high flow rates.The unique technique used in this study is changing the potential surfaces between fines and grain surfaces to prevent fines movement above the critical flow rate.SiO_(2)and MgO NPs used in this study can be adsorbed on the pore surfaces and reduce the repulsion forces between fines and pore surfaces.SiO_(2) and MgO nanoparticles at different concentrations(0.25,0.50 and 0.75 g/L)were used on treating the Abu-Rawash sandstone reservoir using Formation Damage System Cell FDS-350.The experimental studies showed that using MgO NPs would prevent fines detachment from the pore surfaces and decrease the reduction of permeability at high flow rates more than SiO_(2) NPs.The optimum concentration of MgO NPs was at 0.5 g/L as the permeability remediation at this concentration reaches to 64.83%.