INTERVENTION-LESS ZONAL
PRODUCTION INSIGHT

The initial development of inflow tracers was initially designed to provide qualitative information about identifying the location of water breakthrough in production wells. The proof of concept and application for water detection, initiated the development of oil tracers for oil inflow monitoring. Different approaches to install them permanently within a completion component were used, to provide risk free, reliable production monitoring without the need for intervention. Installing unique chemical tracers that are embedded in polymer materials in sand screens or pup joints, along select locations in the lower completion was to correlate where the oil and water is flowing along the production interval and how much. Innovation in the chemistry and materials designed to release to a target fluid (oil or water), enabled non electric wireless monitoring capabilities for many years of longevity in harsh well conditions, such as high temperature and highly acidic stimulation fluids. The evolution of inflow tracer signal interpretation, qualitative and quantitative interpretation workflows using models have also provided valuable insight to inflow characterisation. The latter can provide zonal rate information like wireline conveyed production logging tools, by inducing transients through shut in's or rate changes to create tracer signals that are transported by flow to surface and captured in sample bottles for laboratory analysis. A model based approach to match the measured signals with proprietary models through history matching workflow has also been developed. There are hundreds of well installations utilising inflow tracing monitoring technology today, where the majority have been in open hole completions in both sandstone and naturally fractured carbonate reservoirs on land, offshore environments in both platform and deep water sub-sea environments producing through long tie backs to FPSO's. The monitoring sensors are adaptable to most completion types in conventional and unconventional reservoirs. In most cases, inflow tracers can monitor clean-up efficiency, any subsequent restart and steady state production. Practical case studies will discuss the development of robust and reliable inflow tracer and technology and how operators have applied it over the past decade in a chronological order.

In order to quantify and monitor inflow along the deepest 5,000 ft of a 45,000 ft extended-reach drilling (ERD) well, a (non-radioactive) permanent inflow tracer system was installed, sampled, and analyzed. The tracer technology was piloted as a supplementary downhole data source to the existing practice of intervention-based production logging due to current limitations of intervention accessibility. This application aided in assessing contribution of the lateral segment within a 1-md reservoir quality rock and determining clean-up efficiency.

The deployed lower completion is a 6⅝-in limited entry liner, segmented by packers with design specifically optimized for bullhead stimulation. To meet well objectives, the design of lower completion, along with placement of tracer carrier subs, was geometrically optimized based on expected flow streams. Final deployment included 3 externally vented tracer carrier subs per compartment with optimized spacing, each mounted with a chemically different tracer for both oil and water. A total of 21 distinct signature tracers were deployed per phase within the 7 compartments with compartment length ranging from 681 to 782 ft. In addition, liner is equipped with dissolvable plugged nozzles for efficient mud cake breaker displacement.

Upon activation, the well was flowed for 2 weeks at maximum rate for efficient clean-up before shutting it for 1 week for tracer concentration build up. The well was then flowed, and 106 samples were taken in a decreasing sampling frequency. A subset of 17 samples were selected for analysis – the collected samples were oil with no traces of water. Analysis of the tracer concentration with time showed the arrival of all 21 oil tracer signals and peaks, followed by a decreasing trend towards steady state levels. Results indicate that all reservoir zones contribute to oil production and that all zones have responded similarly in terms of the tracer profiles. This suggests a homogenous reservoir pressure drawdown across all zones. Furthermore, this indicates that reservoir zones cleaned-up efficiently and demonstrates effectiveness of an applied mud cake breaker displacement technique. The tracer results indicate minimum formation damage – in line with expectations, as the target area is a homogeneous 1-md rock quality with uniform reservoir pressure. Using the tracer data, a quantitative interpretation was performed, by use of the so-called flush out tracer transport model. The methodology was successful in determining relative flow contribution per traced zone. Results shows a uniform relative inflow contribution ranging from 4 to 6% per zone. The chemical inflow tracers were deployed in a well with world-record length of 6⅝-in lower completion at 29,243 ft, beyond current accessibility limits of rigless intervention. Also, the well is ranked 5th worldwide (as of time of this writing) in terms of longest well at 45,000 ft, thus making it a world-record in terms of the deepest deployment of chemical inflow tracers.

When analyzing well performance in carbonate reservoirs, the traditional approach usually requires the best practices from pre and post stimulation analysis. Most techniques require an understanding of production performance, which can be divided into two categories. The first is related to reservoir performance away from the wellbore i.e. permeability, fracture network, reservoir pressure, boundaries and secondly, the near wellbore and zonal contribution i.e. permeability-thickness, skin, oil and water influx from individual producing zones. In order to develop a full picture of how these two categories contribute to production performance, a detailed analysis should be conducted to understand their interaction.

Low permeability carbonates and chalk fields often require long multi-stage frac'ed horizontal wells which further complicates the analysis due to lack of measured data in each stage.

The Ekofisk filed development is a mature water flood, which includes both deviated and horizontal wells. Deviated wells are placed in the more crestal location, while the horizontal wells are generally placed towards the flanks where reservoir properties are of lower quality as compared to the field's crest. Production performance and optimization is largely dependent on efficient zonal stimulation, well and reservoir management. Understanding the distribution of fluid phases along the well, especially the water influx, may enable timely executed water shut-offs to mitigate water breakthrough. The traditional technique of understanding where and how much oil and water are being produced, require well intervention through production logging (PLTs). Well interventions are often difficult to execute due to limited access to platforms, the high cost of wells and production deferments. All of these factors limit efficient production optimization due to the inability to collect data in a timely manner for analysis. Furthermore, experiences from the Ekofisk field indicate that PLT data often gives inconclusive results due to known challenges of interpreting PLT data from horizontal wells.

An intervention free and cost efficient approach using inflow tracers has been piloted to acquire early time data, in addition to acquiring well and reservoir understanding throughout the well life. This approach was successfully developed and tested in a newly drilled horizontal Ekofisk field producer. The well was equipped with inflow tracers permanently installed in the completion string to identify individual zone's production contribution including the split by oil, gas and water. In addition, unique intra well tracers were injected into each zone during stimulation to gain knowledge of the stimulation efficiency. During well start up, clean out, transient and post transient production periods extensive sampling programs were executed. As a result, sufficient data has been acquired in order to complete reservoir characterization analysis together with traditional Pressure Transient Analysis (PTA), and then followed by production optimization.

The acquired tracer data and interpretation has been compared with conventional PLT interpretation to verify the former.

This is the first integrated application using permanently installed inflow tracers, injected intra well tracers and pressure data interpretation solution for reservoir characterization and production optimization performed.