Abstract
The advantages of WAG (water-alternating-gas) injection compared to gas injection and waterflooding, from technical and economical points of view, are results of creating a mixed zone in which both water and gas are flowing simultaneously. Previously, an analytical model was developed in the literature to evaluate complete segregation distance and zone distributions for horizontal miscible WAG injection models. Even though this analytical model is derived using simplifying assumptions, it still gives good insight into the design of new projects when the lack of data does not allow a detailed full field reservoir simulation to be carried out. On the other hand, the advantages and disadvantages of applying WAG injection in dipped reservoirs, and up-dip or down-dip patterns are still in question while there isn’t any analytical model available for analyzing process in this type of reservoir. This paper develops analytical equations for a non-horizontal model and investigates the effect of dip angle on segregation effects in miscible WAG injection process. Up-dip versus down-dip WAG injection is another subject which will be discussed in this paper.
Highlights
This paper develops analytical equations for a non-horizontal model and investigates the effect of dip angle on segregation effects in miscible WAG injection process
For several decades, enriched or high-pressure gas injection and injection of miscible slug of liquefied petroleum gas (LPG) chased by lighter hydrocarbon gases as methane have been in the spotlight for enhanced oil recovery, as secondary and tertiary methods, due to their excellent displacement efficiency
It is obvious that saturation distribution of an element in the mixed zone (Figures 1 and 2) will be similar to the horizontal model of Stone (1982) with a minor difference in the heights of different zones, and, for up-dip or down-dip WAG injection, caused by accelerated gravity effect
Summary
For several decades, enriched or high-pressure gas injection and injection of miscible slug of liquefied petroleum gas (LPG) chased by lighter hydrocarbon gases as methane have been in the spotlight for enhanced oil recovery, as secondary and tertiary methods, due to their excellent displacement efficiency. Using a high-pressure glass micromodel, Sohrabi, Danesh, Tehrani and Jamiolahmady (2008) confirmed that near-miscible gas injection gives good recoveries both as a secondary recovery technique and in waterflooded of reservoirs These contradictory results happen mostly because of poor gas sweep efficiency and there are more examples of this mechanism explained in the literature. Stone (1982) believes that injection rate, vertical permeability and density difference between water and gas are the main parameters affecting this distance He used analytical equations to predict complete segregation distance and other boundaries for this process in a homogeneous horizontal reservoir, and compared the prediction with reservoir simulation results. Increased injectivity lets one to inject with higher rates, i.e. higher viscous force, improved sweep and recovery
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