Effect of net confining pressure on formation damage in unconsolidated heavy oil reservoirs

Abstract

It has long been recognized that authigenic clay minerals of various kinds are present within the pore system of most hydrocarbon reservoirs. These clay minerals and other fines may be mobilized during field operations causing permeability reduction. In secondary and tertiary recovery, if the injectivity and productivity of wells are impaired as a result of permeability damage, sweep efficiencies and recovery factors will be adversely affected. The repair of formation damage is usually expensive and difficult; hence, the basic approach should be to prevent damage. To achieve this goal, how formation damage is affected by various system parameters should be known. One of the factors which effects fines migration is the overburden pressure. This is particularly true in the case of unconsolidated formations. However, the authors found no reported investigation of the effect of net confining pressure on fines migration in the literature. This paper presents the results of fines migration experiments carried out in unconsolidated cores from various heavy oil reservoirs in Alberta. The results show that the net confining pressure has a significant effect on fines migration. In particular, it has been found that the critical velocity, at which fines start to be dispersed and permeability starts to decline, decreases with increasing net confining pressure. The reasons behind this phenomenon together with implications for oil field operations are discussed and recommendations are made to prevent this type of damage.