I.5.3.I. Tracer recovery

Among the ten wells monitored for a year, three wells (W2R3D, 214 and 202) yielded positive results for tritium tracer. These same wells also yielded positive returns with NDS. These returns confirmed the communication between the injector well 1R8D and the nearby production wells.

Figure 68 shows the results of the NDS tracer test. Among the wells in Tongonan-1 nearest to 1R8D, wells 2R3D and 2R4D showed NDS breakthrough starting about 19 d after injection. Well 214 manifested breakthrough 40 d after injection, while breakthrough in well 202 occurred much later, at 131 d.

202

FIG 68. Plot showing the breakthrough of wells from NDS tracer injected into well 1R8D.

The wells which showed NDS breakthrough also showed positive returns with tritium; among the wells monitored, these are the only wells which gave tritium breakthrough. Tritium in well 2R3D appeared 28 d after injection; while it appeared in wells 214 and 202, 61 D and 189 d after injection, respectively. The vapour rich wells (i. e. 101, 105 and 109D) did not show a positive manifestation of tritium, even after six months of monitoring, thus analysis in these wells was terminated after December 2006 (Fig. 69).

Tritium and NDS returns in wells 2R3D and 2R4D exhibit sharp breakthroughs at the start and gradually tapered off over time. This is opposed to the relatively semi-broad nature of the graphs for wells 214 and 202. Figure 70 shows the processed curve for well 2R3D for both tritium and NDS tracers. The plots show that there are two pulses of tritium and NDS that entered the well.

Well 214 showed two pulses of HTO breakthrough, while only one pulse was detected for NDS (Fig. 71).

Reduction of HTO and NDS curves in well 202 showed only one pulse for both (Fig. 72). Further, the recovery yield for both NDS and tritium were different. Using the Anduril software, the tracer recovery for tritium was 0.4% for well 2R3D, while wells W214 and W202 both gave yields of 0.1%. NDS recovery, on the other hand, was 1.3% for well 2R3D, 0.2% for well 214 and 0.1% for well 202. On the basis of these results, NDS recovery was higher by almost 100% for wells 2R3D and 214, while recovery was the same for well 202, the well furthest from the injector.