Summary
Jet pumping driven by light oil is one of the preferred lift methods for
producing heavy oil in a deep heavy-oil reservoir. Generally, the amount of
light oil required is too large to be acceptable. One solution which reduces
the amount of light oil required is to blend light oil with a portion of the
produced fluid at a reasonable ratio. Then, the produced fluid/light-oil
mixture is reinjected into the well as the power fluid. In this case, the
viscosity of the blended power fluid keeps increasing and eventually reaches
its equilibrium value, which has been found to be a function of reservoir-oil
viscosity, light-oil viscosity, the ratio of light oil to blended power fluid
(volumetric percentage), and the ratio of well rate to diluent rate (M
ratio). Moreover, an optimal ratio of light oil to blended power fluid can be
determined by using an iterative algorithm developed in this study. Variations
in any of the previously mentioned parameters, especially the viscosity of
light oil and the ratio of light oil to blended power fluid, result in a
significant change in both the viscosity of the blended power fluid and the
pressure loss in the production string. It has been shown in a field
application that the amount of light oil used for driving the jet pumping
operation can be reduced by more than 50%.
Introduction
It is difficult to produce heavy oil from wells deeper than 3000 m using
conventional artificial lift methods (Christ and Petrie 1989). When pumping oil
from a deep heavy-oil reservoir, the sucker rod-pump method undergoes rod
stretch and breakage. The submersible-pump method suffers from high temperature
and thrust-bearing loads at high discharge pressures; furthermore, pump
efficiency is greatly reduced at low production rates. The gas lift method
requires a sufficient and sustainable gas source. In addition, it is expensive
to compress the gas to high pressure and difficult to achieve low submergence.
Therefore, more efficient methods must be sought for producing oil from deep
heavy-oil reservoirs.
The jet pumping method has been proposed as an efficient artificial lifting
technique for heavy-oil production (Cunningham 1957; Petrie et al. 1983a;
Petrie et al. 1983b; Petrie et al. 1984; Tjondrodiputro et al. 1986;
Tjondodiputro et al.1987). In principle, a low-pressure fluid in the reservoir
is boosted and produced by blending it with a high-pressure fluid pumped
downhole from the surface (Fig. 1). Furthermore, the jet pumping method has
advantages for producing oil in deep wells because of its simplicity, lack of
moving parts, small size of pump required, and ability to pump fluids with high
viscosity and/or strong corrosivity. In addition, light oil can be used as the
power fluid in deep heavy-oil wells because it reduces the produced fluid
viscosity and the pressure loss in the production string. The reduction of the
pressure loss can be mainly ascribed to the instantaneous and thorough blending
of the power fluid and the reservoir fluid in the jet pump throat (De Ghetto
and Giunta 1994).
A jet pump is a dynamic pump with a performance curve similar to that of a
centrifugal pump (Brown and O’Brien 1980; Zhang 2000), as shown in Fig. 2. When
light oil is used as the power fluid, the amount of light oil should be enough,
not only to reduce the viscosity of the reservoir fluid in the production
string, but also to provide sufficient energy to lift the reservoir fluid to
the surface.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
25 August 2005
- Meeting paper published:
1 November 2005
- Revised manuscript received:
28 April 2006
- Manuscript approved:
9 May 2006
- Version of record:
20 February 2007
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