iOne number hides seven streams
Operators talk about water capacity as if it were a single quantity. It is at least seven: water generated and separated by train; water treated or transferred to disposal; water injected into disposal wells; water re-injected for pressure support; water sent to evaporation ponds; oil-in-water excursions and recycles; and outages, pump availability and disposal pressure. Each has its own capacity, reliability and way of failing. A plan that respects the headline number and ignores the routes will be surprised by a pump trip.
iiInjectivity is not nameplate
A disposal well has a nameplate injection rate from its design, and an available injectivity at the actual wellhead pressure and formation condition today. The two diverge with time and with solids and oil in the injected water. Capacity planning that uses nameplate overstates disposal headroom by the amount that matters.
iiiPonds are not disposal
Routing water to an evaporation pond relieves the facility today and creates a recovery, environmental and oil-loss problem that comes back later. It belongs in the balance as its own stream, drawn in a different colour, never summed into disposal. On the field in our selected work the agreed convention was disposal and re-injection in two blues and ponds in red.
ivThe oil consequence
Every water limit has an effect upstream: which wells, at which facility, would be cut back if this pump tripped or that well lost injectivity. Writing that consequence next to the limit turns a water balance into a production decision. It also shows which water investment buys the most oil, which is rarely the one closest to the oil.
Water capacity is not one number. It is a set of routes, each with a pressure, a pump and a way to fail.