Unitization of the Minneola field was completed in August 1994 and water flooding started in December 1994. Plots were constructed for each well to trace the monthly production of oil and water at them along with the volume of water injected per month from the nearest injector. These production/injection profiles are presented in Appendix C. Analyses of these production/injection profiles were carried out to determine the influence of permeability distribution and connectivity between the sands on the performance of the waterflood.
As mentioned earlier, storativity and the transmissibility
maps indicate that most of the water injected at well #7-1 is
invading sand #2. Figure 1 shows
that the wells located near injector #7-1 include #9-1, #8-1,
and #6-1. Table 4 lists the producing
sands in each of the wells and it shows that wells #9-1 and #8-1
are both open in sand #2, while well #6-1 is open in both sand
#2 and #3. Well #10-1B is almost equidistant from both the injectors
and its perforation interval is not available. However, production
records show that it has been kept closed through out the water-flooding
period and thus this well was not analyzed in this study.
The production/injection profile for well #9-1 (Figure C1) demonstrates the restriction of the fluid movement in areas of low permeability (obtained from DST) around well #9-1. This results in the dying out of the oil production after the immediate area around the well has been drained. By the time this well is reopened at later date, oil recharges the sand around the well and the well produces for a while again. Production during the second opening of the well exceeds that of the first possibly because some of the injected water at well #7-1 build an oil bank in the direction of this well. The low permeability around the well may also have prevented a breakthrough of injected water. The high permeability around well #8-1 and its proximity to the injector #3-1 resulted in early break through (Figure C2) of injected water. Rapid short-circuit of the injected water may be due to high permeability streaks, and in such a case most of the secondary oil reserves remain unswept in the reservoir. The response to the water flooding becomes apparent in well #6-1 at a later date, than well #8-1, because of its greater distance from the injector and also perhaps due to the lower permeability of sand #2. Only a small oil bank is recovered prior to water breakthrough.
The wells around this injector #3-1 include #3-2, #2-2, #4-1, #5-2, #11-4, #12-2, #13-1, and #1-1. A comparison (Table 4) of the sand interval/s present at the wells and the perforated interval/s in the same well reveals that wells #3-3, #2-2, #4-1, #11-4, and #1-1 produce from sand #2, while wells #5-2 and #13-1 produce from sand #1, and that the perforations in well #12-2 extend through sand #2 on to the top of sand #3. In the vicinity of injector #3-1, both storativity and transmissibility of sand #3 are more than three times those of sand #2. The result is that most of the water is injected into sand #3 in preference to sand #2. However, as none of the wells around this injector is perforated in sand #3, any flood response in these wells will be attributable to hydraulic communication between the sands #2 and #3 in the inter-well region.
Figure C4 shows that well #3-2 had been kept shut for all but 4 months during the waterflood and the reasons are not known. This profile shows some oil production but due to the very short period of flow it is difficult to interpret the performance of this well. Well #2-2 shows a very good response (Figure C5) to the waterflood with no observed water cut. Though this well is perforated in sand #2 only, its oil production closely traces the injection volumes at well #3-1. As most of the injected water is expected to travel into sand #3 from well #3-1, it appears that the flood response in well #2-2 is due to hydraulic communication between sand #2 and #3. The high permeability of sand #2 around well #2-2 must have also helped to maintain performance. Oil and water production curves (Figure C6) of well #4-1 show a response between June to July '97, with the production of a small oil bank being followed by water breakthrough. This well is also completed only in sand #2, and thus hydraulic communication between the sands, good permeability of sand #2 around the well, and its proximity to the injection well may be the factors that attribute to water breakthrough. The first response to the waterflood occurs in well #11-4 between July to August '97 (Figure C7). This well is open only in sand #2 and behaves in manner similar to well #4-1, with water breakthrough following the production of a small oil bank. Such a behavior suggests hydraulic communication between sand #2 and #3 in the region between the injector and the producer. The permeability value in sand #2 for this well is modest (49.2 md) and is lower than that of well #4-1 (88 md). Thus while well #4-1 showed insignificant oil production after water breakthrough, well #11-4 shows continuing oil production even after breakthrough. Performance profile of well #1-1 is traced in Figure C8. Here the response to the flood appears as early as between June and July '95 and suggests communication between the sands #2 and #3. The erratic behavior of the water production suggests that significant reservoir heterogeneity exist between well #1-1 and the nearest injector. Wells #5-2 (Figure C9) and #13-1 (Figure C10) have remained open for short intermittent periods during the course of the waterflood and thus it is difficult to interpret their performance. Also, both of these wells are open in sand #1 and thus may not feel the effects of waterflooding in sand #3. Well #12-2 is perforated in sand #2 primarily with the bottom-most perforation touching the top of sand #3. In spite of low permeabilities both in sand #2 and #3 at the well, water breakthrough occurs as early as Jan '96. However, these low permeabilities might also have resulted in some oil production along with water during the life of the flood.
Production data analysis reveals that response to the water flood is present in most of the wells in the unit plus Hall area. However, reservoir heterogeneity in the form of high permeability streaks appear to short circuit the injected water to the producing well leaving behind significant unswept secondary reserves.
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