Reduction of Light Oil Usage as Power Fluid for Jet Pumping in Deep-Heavy-Oil Reservoirs

Chen, Shengnan (U. of Regina) | Li, Heng (U. of Regina) | Yang, Daoyong (U. of Petroleum E. China) | Zhang, Qi (Tarim Petroleum Ltd) | He, Jun


Jet pumping has been considered as an efficient artificial lifting technique for deep oil production due to its simplicity and lack of moving parts. If light oil is used as power fluid, jet pumping becomes one of the preferred artificial lift methods for the deep-heavy-oil reservoirs by dramatically reducing both viscosity of the reservoir fluid and the pressure loss along the production string. In practice, the amount of light oil required as the power fluid can be as high as three times of the reservoir fluid, among which only a small portion of the light oil is actually needed for viscosity reduction. In this paper, a novel technique has been developed and successfully applied to significantly reduce the amount of light oil usage in a deep-heavyoil reservoir. More specifically, two approaches are developed and compared. As for Approach A, the oil well is produced with jet pumping driven by light oil first, and then the produced fluid is reinjected into the well as the power fluid. This process keeps circulating until viscosity of the produced fluid is too high to be utilized for jet pumping. As for Approach B, partial produced fluid is combined with the light oil at any reasonable ratios, and subsequently the produced fluid-light oil mixture is reinjected into the well as the power fluid. In the latter approach, viscosity of the mixture keeps increasing and will reach its equilibrium value in a few days, and thus, stable production will be achieved as well. Theoretic models are developed to determine the viscosity of the power fluid for each circulation and the maximum cycle number for the former approach as well as the equilibrium viscosity of the mixed power fluid and the optimum ratio of light oil to the produced fluid-light oil mixture for the latter approach. Field applications show that the reservoir fluid produced from deep heavy oil wells is increased by three times and that the amount of light oil can be reduced by more than 60% for either approach.

1. Introduction
Deep-heavy-oil reservoirs, usually referred to those with depth of more than 3000 m (Christ and Petrie 1989), are different from the conventional heavy oil reservoirs. In general, reservoir fluid can flow more easily in the formation as well as around the bottomhole in a deep heavy oil well at a higher temperature. However, during its path along the production string, viscosity of the reservoir fluid increases dramatically due to heat loss and release of the dissolved gas, which results in great pressure drop along the wellbore. Thus, artificial lifting methods need to be adopted to pump the reservoir fluids to the surface.

Among the artificial lifting techniques, jet pumping has been proven to be an efficient method in producing oil from deep heavy oil reservoirs (Cunningham 1957; Petrie et al. 1983a; Petrie et al. 1983b; Petrie et al. 1984; Tjondrodiputro et al. 1986; Tjondodiputro et al. 1987). Jet pump is a venturi-type device where a high-pressure power fluid is used to accelerate to reach a higher velocity and thereby create a lower pressure area into which reservoir fluids will flow (Mueller 1964). Because of its small size, simplicity, lack of moving parts, a jet pump can be installed in the wellbore at a deep location. It also has a strong ability to pump fluids with high viscosity and/or serious corrosivity (Petrie et al. 1983c). For heavy oil production, light oil can be used as the power fluid because it reduces viscosity of the reservoir fluid and the pressure drop in the production string as well (Qu et al. 2000). The reduction of the pressure drop is mainly ascribed to instantaneous and thorough blending of the light oil and the reservoir fluid in the jet pump throat (De Ghetto et al. 1994).