ABSTRACT

Selective shutoff of undesired water influx by nonselective (fullbore) placement of treating chemicals has been successfully demonstrated in production wells of the Prudhoe Bay field. This was accomplished through:

  1. careful choice of candidates with known high conductivity water influx pathways (fault, hydraulic fracture, thief),

  2. placement that exploited conductivity differences without zonal isolation, and

  3. use of established polymer gel chemistry with previously demonstrated ability to shut off water preferentially to oil.

INTRODUCTION

Waterflooding at Prudhoe Bay was initiated in 1983. Currently there are more than 160 water or water-alternating. gas injection wells in operation, supporting, in inverted nine-spot patterns, 480-plus producers. Due to waterflood maturity, a significant number of producers have watercuts of 90% or higher. While most of the water produced is necessary for oil recovery, there are a number of occurrences of influx from watered-out zones or from the underlying Sadlerochit aquifer that contribute to water cut, but not to oil production.

Wellbore treatments with cement (coiled tubing perforation squeezes) have been successfully used to shut off unwanted water influx from cement channels or from hydraulically isolated zones in unfractured production wells.1,2 Similar treatments have been employed to delay coning from bottom water caused by movement of water-oil-contact. However, wellbore shutoff has been only partially successful at controlling water influx from offending zones that are not hydraulically isolated from desired producing intervals. Furthermore, in cases where influx is via a segment of a hydraulic fracture that has inadvertently penetrated a water zone, a wellbore treatment is not expected to have much, if any, effect on water cut, without sacrifice of the entire fracture's connectivity to the wellbore, with corresponding loss of oil rate.

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