An offshore customer was reaching the final stages in the development of an offshore sub-sea well that was to be stimulated using hydrochloric acid as part of the completion process. As the well was serviced by a mobile drilling rig the client wished to determine relative flow contribution from each of the stimulated zones that were isolated from each other using packers and sliding sleeves without the costly use of a Production Logging Tool (PLT). The Tracerco Acid tagging technology was selected to meet their requirements.
The horizontal oil well was drilled to a TVD of 3902 meters. It consisted of a 7" casing with seven unique zones along its horizontal length each completed using a sliding sleeve arrangement on 51/2" base pipe. The total horizontal section was 1,050 meters with each of the seven isolated zones with a length of around 150 meters each.
Application of the Technology
The technique involved the injection of seven water based chemical tracers during the acid stimulation program. At a specific time during each stimulation stage, water based chemical tracer was added at the suction side of the acid pumps directly into the flowing liquid. A unique water tracer was used for each stage of the operation. The activity did not have any operational impact during the stimulation.
Sampling and Analysis
After the stimulation was completed and during well cleanup operations, commingled oil and water samples were taken on a regular basis. The samples were sent to the specialist Tracerco laboratory. The water was separated from the oil. Analysis was carried out on each sample to measure the presence and quantity of each of the unique chemical tracers added during the stimulation treatment. Measurement of the presence and amount of each chemical gave an indication of whether each zone was contributing to the overall production. The amount of tracer returning from each of the zones was used to gain an understanding of the proportion of well-bore flow contribution from each.
Results of the analysis revealed that only three of the seven water based tracers were detected in surface samples (see figure 1). These tracers were positioned in zones one, three and seven. Integration of the tracer response showed a relatively even contribution from the three zones of 34, 29 and 37% respectively. As the well was showing weak production the customer decided to enter the well and check to make sure that all the sliding sleeves were open. As part of the intervention, they also decided to run a PLT to better understand why flow was so weak. During the intervention it was confirmed that all sleeves were open. The PLT run (figure 2) showed that most of the production was originating from zones one, three and seven with some contribution from zones four and five.
Tracerco offers water, oil and gas based in-flow chemical tracer technology during stimulation activities.
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