Streamlines are the paths that fluid particles follow when they move from the injector to the producer a streamtube is the region between two streamlines. In the 1960s, Higgins and Leighton published a technique for analyzing waterfloods using what has been termed streamtubes, or stream channels, and using the concept of streamlines. When the oil is less viscous than the water, the water areally displaces the oil very efficiently. When the oil is more viscous than the water, the water areally displaces the oil less efficiently. 2 through 4 show that the water/oil viscosity ratio is critical to the efficiency of the waterflood displacement. The horizontal lines indicate what the range of mobility ratios M would be if it were calculated using the water mobility at floodout conditions (the right extremity of the horizontal bar) or using the water mobility at the flood front (the left extremity of the bar), with the arrows indicating that the values were off the scale of this plot.įigs. On this figure, the mobility M has been calculated using the average water saturation in the water-contacted portion of the reservoir. 4 – Correlation of areal sweep efficiency at breakthrough with mobility ratio for miscible and immiscible displacement in five-spot-pattern floods.
4 plots the breakthrough areal-sweep efficiency as a function of M for a five-spot-pattern flood.įig.
3 shows the X-ray shadowgraphs of a waterflood of two five-spot homogeneous sandpacks, one whose mobility ratio is favorable ( M = 0.40) and one whose mobility ratio is unfavorable ( M = 1.43). 2 plots the waterflood performance of a five-spot experimental homogeneous sandpack for range of water/oil viscosity ratios from 0.83 (slightly favorable) to 754.0 (very unfavorable). 1) provides an effective review of the areal aspects of waterflooding. Waterflood displacement in a five-spot patternīecause it has been studied extensively, taking a look at the five-spot pattern ( Fig. 4 Horizontal wells, multilateral wells, and fracture orientation.3 Waterflood pattern and well spacing considerations.1 Waterflood displacement in a five-spot pattern.
For offshore oil fields where the maximum number of wells is limited, the optimal waterflood injection-well/production-well layout is best determined by the use of 3D numerical reservoir simulation. This has been particularly true for onshore oil fields in the US in which a significant number of wells were drilled for primary production. Maximizing the ultimate oil recovery and economic return from waterflooding requires making many pattern- and spacing-related decisions when secondary recovery is evaluated. The primary areal considerations for a waterflood involve the choices of the pattern style (see Fig. To simplify 3D to 2D areal, either the reservoir must be assumed to be vertically a thin and homogeneous rock interval (hence having no gravity considerations) or one of the published techniques to handle the vertical heterogeneity and expected gravity effects within the context of a 2D-areal calculation must be used. Before computer modeling was common, the 3D aspects of a waterflood evaluation were simplified so that the technical problem could be treated as either a 2D-areal problem or a 2D-vertical problem.
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