An operator was developing an oil field using sliding sleeve completions. Hydraulic packers were used to isolate specific sections of the well. During previous well completions there was uncertainty on oil contributions from each zone. In addition, there was uncertainty where injection water would breakthrough into the well. It was determined that the use of controlled release chemical tracer technology would provide the operator valuable inflow data without the need for well intervention.
In total six sliding sleeves were run across an 1,800 feet horizontal production zone with packers set every 300 feet. A number of unique oil and water soluble tracers were added to the production string using pup joints with an external shroud containing the tracer material. The shroud was sized to ensure that its outer diameter (O.D.) was slightly smaller than the packer O.D. Running in hole. Figure 1 shows the modified pup joint design and figure 2 how each oil and water tracer was positioned in the production tubing.
Tracerco manufactured the pup joints using customer base pipe to meet all necessary technical and quality requirements. These were delivered to the field directly from Tracerco. The customer integrated each pup joint into the completion design such that it was located close by each sliding sleeve inlet position to maximise flow rate across their surface. No additional rig time or man time was required as part of this process.
Sampling and Analysis
Tracerco field technologists took the samples, due to the importance of sampling over short time periods at the beginning of first oil during the clean up and production. Samples were taken at very regular intervals after displacement of completion fluid and first oil was detected for the first 24 hours. This allowed the initial concentrated pulse of oil tracers to be measured accurately. After two days of sampling, when their frequency had reduced to four samples per day, Tracerco handed responsibility for sampling to site staff. Samples were taken on a regular basis and sent to Tracerco for analysis.
Results and Interpretation
Tracer response data is shown in figure 3. It can be seen that five of the six tracer positions were flowing. The position closest to the toe of the well showed zero flow throughout the sampling time period. No water was present within the well. Water tracer analysis shall begin as soon as water breakthrough occurs in the well to determine where it is flowing into the wellbore.
A comparison was made between expected tracer response timing (figure 4) based upon production tubing volumes and flow rate from the well during clean up and actual tracer data (figure 3). This allowed a semi quantitative analysis of relative oil flow contribution from each of the sliding sleeves. Table 1 shows results of data analysis showing the contributions from each sleeve section.
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