Some Old Oil and Gas Fields Have Lithium Rich Water• https://www.nextbigfuture.com, by Brian Wang
This depends on the basin, since produced water mineral presence and concentrations can vary widely play-by-play, and even within the basins themselves, depending on the geology.
Subsurface or deep aquifer brines are abundant in Alberta and Saskatchewan oil and gas field and some of those have elevated lithium concentrations and are potential resources. Brines can have about 10000 times higher concentrations of lithium than in seawater. The best brine sources (notably the Salar de Atacama in Chile) can reach 5000 parts per million (ppm) lithium. As a rough rule of thumb, brines with less than 400 ppm lithium may not be economical to recover with today's tech. The world's oceans contain an estimated 180 billion tons of lithium. But it's dilute, present at roughly 0.2 parts per million. Marginal brines have 2000 times the concentration of lithium compared to the oceans.
One tonne of lithium content is obtained from 5.3 tonnes of lithium carbonate (Li2CO3).
One tonne of lithium can be obtained from ~37 to 43 tonnes of spodumene concentrate.
The brine process involves drilling wells and pump the brine from underground into a series of evaporation ponds. In dry desert climates, the water in the brine evaporates, leaving behind a brine with even higher mineral content (basically a salty mud). Once the lithium content reaches target levels (up to 6% by weight), the highly concentrated brine is sent via pipeline or tank truck to a lithium processing facility.