Conventional downhole dynamic characterization generally consists of fluid typing and profiling by means of standard production logging strings, which include pressure, temperature, hold-up and spinner probes. This approach cannot be applied in challenging environments characterized by asphaltenes, waxes and solids presence inside the completion that prevent any reliable measurements. This paper discusses the use of advanced and alternative techniques aimed at properly describing the dynamics of such complex scenarios and based on tools without mechanical components.
Fiber-optic distributed sensing conveyed through coiled-tubing is used to monitor in real time well completion integrity, post-stimulation job efficiency and fluid flow behavior by means of temperature (DTS - Distributed Temperature Sensing) and acoustic (DAS - Distributed Acoustic Sensing) measurements. Moreover, the acquisition of eccentralized oxygen activation (OA) and noise log data in a wide frequency range (WFN - Wide Frequency Noise) complements the dynamic characterization from a quantitative standpoint. In details, OA logging, based on pulsed neutron technology, identifies the water entry points and can be used to estimate the water velocity. On the other hand, the WFN log records the noise generated by the fluid flow and allows a direct understanding of bulk flow path in the near wellbore region. Finally, an in-house methodology provides the relative allocation of the produced fluids, both in wellbore and reservoir, after a quantitative spectral analysis of noise log data.
The added value of the innovative technologies is demonstrated by means of a study performed on different wells drilled in a naturally fractured carbonate reservoir. The long and horizontal drains are completed with slotted liners, are stimulated with acid treatment and are characterized by fast asphaltenes deposition. In particular, the outcomes of the enhanced interpretations of retrievable fiberoptic DTS and DAS, OA and WFN log data have been successfully used for production optimization purposes. This fact illustrates the reliability of mentioned technologies and suggests a robust modus operandi as alternative to conventional production logging techniques.
Generally, cased-hole (CH) analyses are aimed at understanding well and reservoir behavior in order to optimize lifetime production. In particular, specific tools have been developed to address wellbore integrity issues, such as sonic/ultrasonic cement logs, and for the reservoir dynamic characterization, mainly with conventional production logging tool (PLT) strings [1].
However, these standard techniques utilize mechanical components and may have some operative limitations in challenging environments characterized by asphaltenes, waxes and solids depositions that can prevent well accessibility and/or any reliable downhole measurements.
