Fines migration and change in hydraulic conductivity caused by multiphase flows in sands

Abstract

When depressurization method is applied to the methane hydrate-bearing sediment, prediction of fluidly induced movement of particles plays an important role in methane gas production. The fine grains of the hydrate deposit layer are moved due to the flow of the fluid generated during the depressurization, and the movement of such fine grains is the main reason for the shear failure of the well and the decrease in productivity. Movement of particles induced by fluid flow is influenced not only by characteristics of fine particles but also by characteristics of fluid and characteristics of host network. These characteristics are combined to determine the nature of the fines migration. Those combinations of properties determine the nature of fines migration, and that makes difficulties in predicting the movement of fine particles and its generalizations. The aspect of particle movement at the present time is not yet fully considered in both the simulation and the field. In this study, it is designed to see migration and pore blockage behavior of fine grains by multiphase fluid flowing through sand network using 1D flow cell. Ottawa 20/30 sand is used as a host sediment and for the fines both kaolinite clay and silica silt are used. Two samples with high and low fines content are used for the sample. The single phase flow test conduct by making water flow, and multiphase fluid test conduct by mixing air bubbles to this. The pressure gradient during the experiment is monitored, and collect the sample in 5 parts after the experiment. The final fines content is obtained as the average value of the sampling result after experiment. Factor that have the greatest influence on the movement of fine granules have been revealed to the type of fine granules through experiments. In all cases, the movement of the clay was smaller than the silt. This is explained with two properties of clay particles. One is the effect of surface charge and the other is flocculants structures when they flow through the network. In the sample mixed with the same particles, the amount of initial fine particles does not have a large influence. The results show that fine grains are produced at a constant rate regardless of the amount of initial fine grains. The presence or absence of air greatly affect the movement of particles. It is considered that the effect of the capillary effect and the surface charge acting on the particle at the air-water interface increased the movement of the particle. Based on the permeability measured through the experiment and the fines content, it is compared with the permeability predicted using the Kozeny-Carman model. The Kozeny-Carman model well predicts the change in permeability according to the fines content of silt mixed samples, but the result of clay mixture did not match with the Kozeny-Carman model. This discrepancy is caused by the local fines migration in the mixed sample of clay greatly affects the water permeability but the local fines content is not displayed in the section fines content.