Effects of Oil-Water Mobility on Injectivity Impairment due to Suspended Particles

Abstract

Injectivity decline during sea/produced water injection is a wide spread phenomenon in offshore and onshore waterflood projects. It happens due to solid and liquid particles suspended in the injected water; their capture by the rock results in the hydraulic resistivity increase. The field injectivity decline history is used for characterisation of the formation damage system and consequent well behaviour prediction. The injectivity index increases M times during the damage-free displacement of oil by water (M is the water-oil mobility ratio). It affects the well injectivity prediction during poor quality water injection and changes the results of injectivity decline curves interpretation. We study the combined effect of the particle suspension injection and of the total oil-water mobility variation on well injectivity. An explicit formula for injectivity decline due to both effects was derived. The effect of the total oil-water mobility variation on injectivity is particularly significant for cases of heavy oil and relatively low formation damage. The injectivity decline formula derived allows for determination of filtration and formation damage coefficients and filter cake permeability from the well injectivity history. Two examples of well data treatment for the deep-water offshore reservoir A (Campos Basin, Brazil) are presented.