Exploring the Downhole Waterways: Identification of the Sneaky Path of Water Through the Well Completion

Abstract

In highly deviated/horizontal wells, understanding the downhole water entry points and the effectiveness of the completion barriers are paramount challenges for a proper production management and for a prospective water shut-off design. The integration of hybrid cable with a mono-conductor and optical fiber (Distributed Temperature/Acoustic Sensing, or DTS/DAS), pulsed neutron-based Water Flow Log (WFL) and Production Logging (PL) can provide information about the downhole flow profiling, the water producing zones and the failures of the completion hydraulic seals. This paper discusses an optimized data acquisition and interpretation workflow tailored for such highly complex well scenarios. The reference case study is Well A, an onshore horizontal oil producer intercepting a naturally fractured carbonate reservoir. The horizontal drain was completed with slotted liners in front of faults and fractures identified as the main oil entry points. Fast asphaltenes deposition makes this environment challenging for tool stuck risks, hence conventional PL tool strings are not usable during production. After initial outstanding performances, Well A started to suffer from a huge water-cut with consequent impact on production and surface facilities. The acquisition and the interpretation of a combo DTS and WFL conveyed via coiled tubing provided a clear picture of the downhole flow profile highlighting a strong water production in the shallower part of the drain. The horizontal drain was then temporary excluded with a bridge plug and a batch of specific sealant polymer in order to hydraulically isolate inside and behind the pipe. A new interval was then opened to production with through-tubing perforations. Unfortunately, at the well restart, the production performance was similar to pre-isolation and perforation, still with an important water contribution. Hence, a spinner-based PL string, combined with an inverted WFL, was utilized to investigate the new perforated interval and the isolation of the bottom of completion. The log acquisition was performed during brine injection to overcome the risk of tool stuck due to the asphaltene deposition during production. It is well-known that collecting reliable data is the starting point for the design of a proper operation aimed at excluding hydraulic communication with an abandoned drain. This experience confirmed the possibility to acquire strategic information in challenging producer wells during brine injection and using a combo PL-WFL for fluid path discrimination inside and outside the completion environment. Auxiliary pulsed neutron log outcomes, such as the Compton ratios, can be used to define the actual region of the communication behind casing.