Effective Cross Flow Diagnostic by Pulse Neutron, Cement Logs and Fluid Production: Water Shut Off Well Case in Amo Field

Abstract

The high water cut 98,5% caused the abandonment of a directional well, which was reactivated after 3 years using a water shut off technique. Offset wells production behavior, stratigraphic seal layers distribution, reservoir properties, and cased hole logging data played a relevant role for the well planning, reactivation and production success of heavy oil from the mature Amo field in the Oriente Basin of Ecuador. The Lower U reservoir production screening from neighbor wells and stratigraphical well correlation supported a rigless acquisition plan of pulse neutron logs to diagnose the fluid flow patterns after 5 years of production and 3 years of a well abandonment. Further corrosion and cement log was run to check the well integrity and compared it with initial cement log to discard possible cement channeling suspicion behind casing. Finally, water shut off well program was carried out. The acquired neutron logs showed flushed zone from two former producing perforations as well as remaining hydrocarbons in the upper perforated zone. The gamma ray log activation was detected just below the oil water contact while the oxygen activation log "OAI" was highlighted just above the gamma ray activation at the same depth where CBL log experienced picks perturbations suggesting bad cement an possible channeling behind casing. The OAI ended just in the upper unit perforations where another CBL pick was recorded. These evidences supported possible cross flow hypothesis from the bottom to the top producing zones. The water shut off job squeezed the lower perforation zone and re-perforated the upper unit to reactivate the abandoned well. The cement and corrosion logs suggested a good conditions of casing and zone isolation from aquifer. The well reactivation produced 700 bbl/d of water formation (100% BSW) during a month, the water salinity gradually increased from 16000 ppm to 45000 ppm NaCl. Likewise water cut diminished to 17% and 170 bbl of oil was pumped daily after voiding the cross flowed fluid (44000 bbl). Furthemore, the unknown productivity index for ESP pump design was unveiled. Stratigraphic well correlation indicated the shale layer continuity and thickness variability, which in combination with shale buffers occurrence were controlling the production behavior in offset wells. These aspects led to get updated cased hole logging data to identify opportunities for re-activation of abandoned well unlocking by-passed oil reserves after successful water shut off job execution.