Near Real-Time Tracer Data from the Onsite Tracer Analysis in Nova Field

Abstract

This paper describes how near real-time tracer data from the onsite tracer analysis enabled the operator in the Nova field to interactively optimize two well clean-ups to the rig. The tracers provided key information on the clean-up progress in different zones which enabled the operator to make informed and fast decisions to maximize well clean-up efficiency while minimising rig time and cost. Verification of well clean-up to increase zonal productivity and to eliminate the risk of damage to the surface production unit with minimum rig time is always a challenge during well start-up. The conventional wellbore clean-up practices are to monitor surface parameters including produced mud volume and basic sediment and water (BS&W) in the production fluids until a certain criterion for these parameters are met. However, this method cannot confirm that all the zones are cleaned up and are contributing to the production. Having the right monitoring technology to confirm well clean-up at the zonal level is therefore essential to successfully clean up the entire reservoir section. Inflow tracers with onsite analysis provide near real-time data on clean-up efficiency in different zones. Unique tracer molecules are embedded into the polymer systems and permanently installed in the lower completion. Oil and water tracers remain dormant until they come into contact with their target fluids. Once activated, the tracers are released into the target fluid for a certain designed life period and can be sampled when the well is opened. The collected samples can be analysed onsite or offsite at a laboratory. The onsite analysis can provide near real-time data and is preferred for a fast decision-making process such as during the clean-up to rig. The Nova drilling plan consisted of three oil producers (two horizontal and one slanted). The onsite tracer analysis with fast analysis turnaround time was used for the two horizontal wells. For the first horizontal well (X-3H), the tracer data results confirmed a strong heel clean-up efficiency from the very beginning and a weak toe clean-up efficiency. The middle and toe zone tracers appeared 8 and 12 hrs after opening the well respectively, therefore confirming oil contribution from all zones. Due to weak clean-up at the toe, the operator decided to prolong the clean-up at maximum drawdown to improve the clean-up of the toe section. For the second well (X-4 AHT2), the toe section exhibited effective clean-up from the very beginning while the heel zone showed a gradual clean-up and started to clean up 10 hrs after opening the well. Monitoring well performance at the zonal level without any intervention and in a cost-effective manner is a challenge, especially during the initial opening of the well to the rig. In this case, the inflow tracer technology was successfully utilized to provide near real-time validation of clean-up and flow contribution. This enabled the operator to understand his wells’ behaviour and make real-time decision to increase the clean-up efficiency and zonal productivity while efficiently using the rig time during the field development phase.