An oil field operator wished to better understand communication pathways within an inverted nine spot waterflood operation. This was to establish:
The pattern area under investigation consisted of four injection wells and associated producers.
Tracerco selected a unique chemical tracer for each injection well out of their 20+ proven chemical tracer portfolio. Using reservoir and fluid flow data a project plan was developed. As there was uncertainty with respect to fracture as well as matrix flow, the injection and sampling strategy was designed with the expectation that rapid breakthrough could occur.
Tracerco injected two kilos of each of the unique tracers into the wells over one day with no disruption to normal operations. Alongside injection, other Tracerco crew sampled production wells on a regular basis for the first three days. As planned sampling frequency reduced over time, the sampling program was handed across to operator staff to continue.
Sampling and Analysis
Tracer was detected in a number of production wells. The field map in figure 1 shows the communication pathways between injection and production wells.
The tracer elution curve from one of the wells, S-10-03, together with recovery over time is shown in figure 2. Further analysis of each recovered tracer type allowed a normalisation calculation to determine the percentage of injection water flowing to producing wells and the source of produced water to be calculated for each production well. Figure 3 shows the percentage split of injection water for each of S-10-08I and S10-15I as well as the percentage production water originating from the two injectors at producer S10-03.
Interpretation of Results
Results proved a preferential flow trend in an East North East to West South West direction within the field and showed significant none contacted areas within the pattern flood. This will allow the operator to better balance flood throughout the area and consider in-fill drilling improving efficiency and ultimately production.
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