When improving field production, the traditional focus on drilling activity means that the benefits from effective Well and Reservoir Management (WRM) are often overlooked. Within Sakhalin Energy’s Astokh area, an integrated field management approach has realized significant oil gains with minimal well interventions.

When phase 1 of the Astokh development was completed in 2001, only seasonal production via an FSO was available. Associated gas was re-injected into the crest of the reservoir, leading to a secondary gas cap. When this caused gas coning in updip wells, oil production declined because the gas handling equipment limits were exceeded. Pressure maintenance wells in 2004 helped to minimise associated gas levels, but it was not until the Sakhalin Energy Phase 2 project came on stream in 2009 that year round export was available, allowing gas injection to cease. With the drilling rig not available until Q4 2011, the application of effective well and reservoir management was the only way to address the declining field production.

The primary focus was the depletion of the secondary gas cap. The first decision was to open high GOR updip wells whilst managing others through downhole shut-off / choking of zones. Secondly, water injection well volumes were optimized depending on levels of gas cap depletion in various areas of the reservoir. Thirdly, the reservoir model was regularly updated, reflecting gas cap behaviour seen through GOR levels in updip wells. Executing this approach required the gas compression facilities to operate at > 100% efficiency and put strain on the equipment, so a significant effort to maintain the reliability of the surface facilities was pursued.

Within a year of implementing this multi disciplinary approach, three wells more than doubled their oil production rates.

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