Five-spot Flooding (M=1)

Objective

The following experiment aims to demonstrate the effects of mobility ratio on areal sweep efficiency of a five spot waterflood.  This was achieved by determining the displaceable fluid volume, the efficiency of areal sweep as a function of produced fluid volume and finding the breakthrough point.  In other words, the main goal of this experiment was to determine the mobility ratios at different points and determining the breakthrough points in an ideal five spot waterflood. 

Description

The experiment consisted of a square sandstone core which was initially flooded with clear naphtha and sealed on the top, bottom, sides, and two corners with epoxy to prevent fluid escape. The sandstone also had one free corner attached to a pipe that simulated the production of reservoir and injected fluids. The other free corner was attached to a pump that was used to deliver dyed naphtha at a constant pressure. 

Experimental Apparatus Diagram

Experimental Procedure

The dyed naphtha was injected at a constant pressure drop until it began to forma a displacement pattern. A tracing paper was used to record this pattern and reported as a function of time. The time and produced fluid volume was recorded at each tracing, a process that continued until injected fluid breakthrough was observed. Several additional reading were taken after fluid breakthrough was observed , which was used to create plots showing the areal sweep efficiency versus injected fluid, and areal sweep efficiency versus a normalized fluid injection volume. The data obtained from this experiment was used to demonstrate the effect of mobility on sweep efficiency and fluid conductivity.

Data of the Experiment

Front	Time (sec)	Cum. Volume	Area Swept	%		SPE Paper
1	32	4	5.31	5.31	0.02631579	0	0
2	131	19	13.84	13.84	0.125	0	0
3	309	39	26.55	26.55	0.25657895	0	0
4	586	68	42.79	42.79	0.44736842	0	0
5	832	92	56.89	56.89	0.60526316	0	0
6	1030	112	70.17	70.17	0.73684211	0.15	0.73
7	1238	132	78.06	78.06	0.86842105	0.45	0.85
8	1414	150	82.24	82.24	0.98684211	0.62	0.91
9	1616	172	87.36	87.36	1.13157895	0.7	1.1
10	1906	200	90.11	90.11	1.31578947	0.81	1.23

Results and Discussion

Green circle indicates the water breakthrough at 78.06 cc while the black circle indicates the displaceable pore volume, (Vd).

The experimental data obtained decently agrees with the data obtained from the original SPE paper. The experiment indicates a linear increase in the area sweep efficiency up to a point of water breakthrough at 78.06 cc. At this point, the sweep efficiency starts leveling off, and therefore indicating that the reservoir is no longer producing reservoir fluids only. The curvature in the graph after the breakthrough indicates the production of injected fluids. Extrapolation from the linear segment of the graph helps to determine the total volume of displaceable fluids to be 152 cc.  Using this value, the injected volume was normalized to total pore volume, and areal sweep efficiency was plotted against the normalized axis. The graph formed shows behave linearly, with its slope approximately similar to the first graph. The unity slope indicates that no injection fluids are being produced. As the breakthrough starts, the slope approaches zero, showing that the injected fluids are growing in terms of produced volume fraction. The slopes were determined using a first order backward difference formula. Results indicate that the reservoir will begin to produce mostly injected fluids after breakthrough. 

Conclusion

The experimental setup produces results that are comparable to each other. Both show a linear trend in areal sweep efficiency versus normalized injected fluid volume prior to water breakthrough. Both begin to show curvature in the graph after water breakthrough occurs. Using these results, it is possible to determine the fraction of produced fluids that will be injected fluids. For a unity mobility ratio, this can be used to predict the point of water breakthrough after extrapolating the total volume of displaceable fluids. Consequently, these plots can be used to evaluate the economics of an injection technique.