From hot water to working water: observations from the geothermal industry
Waterflooding in mature fields can offer significant recovery factor increases and extend the economic life of an asset. However, often the level of detail dedicated to understanding how the reservoir(s) will react to injection at the initial stage is not sufficient to realize the full potential of this optimization technique.
From the earliest stages of modern geothermal developments, optimizing re-injection of spent fluid is usually essential to the life of the development. To help ensure effective management of thermal breakthrough and field connectivity risks, operators must incorporate a high level of detail regarding the placement and management of injection volumes in different areas of the reservoir. These factors can have a large impact on the fluid enthalpy and electricity generation potential. Similarly, applying this level of early-stage detail to waterflood techniques application can help achieve the greatest possible recovery potential for mature fields. Not properly understanding the reaction of the reservoir-to-water injection can, in some cases, be detrimental to oil production.
For geothermal developments, an understanding of local groundwater aquifers and the ability of the reservoir to pull on cooler peripheral fluids is essential. Output can drop due to peripheral fluid or injection breakthrough, requiring production modification or a new injection strategy to curtail the impact. Ohaaki (New Zealand) experienced an output drop from ~100MW to ~40MW due to peripheral fluid influx. Tiwi (Philippines) experienced reservoir temperature drops from infield injection breakthrough, also impacting output. The correlative point is that with waterflooding—as with geothermal techniques—your injection is almost as important as your production.
Based on experience and learnings, the geothermal industry now works to help ensure full injection optimization at the earliest stage possible to maximize field performance over time. From the outset, the same discipline should be applied to waterflooding techniques.
Not optimizing waterflood techniques at an early stage can result in a significant effort later in achieving a satisfactory result. This was the case in the Maracaibo Basin (Venezuela) where multiple waterflooding efforts were unsuccessful in optimizing recovery over a period of 40 years. A considerable reassessment was then required to find an optimal solution.
While watered out or non-producing wells can be attractive candidates for injection offering easy access to the reservoir, insufficient planning can result in waterflooding less than optimal locations. As in modern geothermal developments, waterflood techniques should include upfront adequate effort to understand fluid flow dynamics, meaning a strong, integrated, resource conceptual model encompassing both geoscientific and reservoir engineering data. This effort is important because it forms the basis for numerical simulation of the reservoir, which will help govern the location and volumes of injection.
The impact of injection might change with time; therefore, frequent reviews of the strategy as more information becomes available are critical—the model is only as good as its input. Operators must understand how the changing physics underground affect the simulation. No two reservoirs are the same.
If operators implement an early-stage, detailed approach to waterfloods the results can offer prolonged, increased recovery and the ability to better understand and adapt to changes in the reservoir. The approach requires a subsurface understanding focusing not only on the oil but on the nature of the hydrology of associated aquifers and permeable pathways. Running multiple scenarios for the subsurface and economic constraints will help ensure the appropriate plan is in place.
|Treat water injection as seriously as you treat production.|
|Make sure you have an integrated understanding of the subsurface.|
|Ensure your dynamic simulation represents the physics of what is occurring in the reservoir and the surrounding aquifers.|
|Every reservoir is different and requires a unique injection strategy.|