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The water shut off technique is applied in some wells as a remediation plan to restore their production after an early water breakthrough from U reservoir in the Iro field of the Oriente Basin, Ecuador. The production historical data, workovers and sandbodies correlation are compared among wells to understand the reservoir behavior, the shale baffle sealing continuity, the existence of different sand units and the impact on their production. Few years of heavy oil production with abrupt water increase conducted to squeeze perforations in the lower part of pay zones. Production behavior before and after water shut off is analyzed regarding water cut, formation water salinity, fluid provenance from the reservoir and its zone perforations setting during completions. The stratigraphic well correlation, reservoir properties and sealing shale layers explain the well production outcomes and geological patterns. Well intervention lessons learned and recent pulse neutron logs support additional water shut off proposals at current Iro producer wells. The U sandstone reservoir development was focused on the Lower U sequence while hydrocarbon potential was identified in Upper U sequence. Nevertheless, the geoscientist kept the main interest in Lower U reservoir development because of their oil in place volume. The strong water drive aquifer caused mostly a fast water cut increase achieving 90% in around three months and well’s production continued for few years until economical cut. In order to keep wells in active status, squeeze jobs were planned and executed, dropping the water cut to less than 10% followed by a gradual ramp up during many years of production. The fluid rates were reduced drastically from average 10000 bfpd to less than 1500 bfpd. The formation water salinity increased from 18000 ppm to 60000 ppm. These evidences advice of two different production behavior in the Lower U sandstone reservoir. The re-perforations were done above a shale layer seal which separates sandstone units. This seal is controlling the water breakthrough in many wells. However, there is evidence of sandstone units connection to the western area of the field, because of salinity decrease and pressure increase. After many years of production, pulse neutron logging was run showing flushed zone from former producing perforations as well as remaining hydrocarbons at thin sandstone layers deposited in the upper unit of Lower U sandstone reservoir. In addition, this document will allow reservoir engineers to forecast production behavior, to plan water shut off in analog fields, accordingly. |
