EOR screening: the right method for the right reservoir.
Chemistry, steam or gas? Before injecting anything, you interrogate the reservoir. Gravity, viscosity, depth, temperature, permeability: five measurements that decide the method — and avoid costly mistakes.
Enhanced oil recovery promises striking numbers — up to 17 more points of OOIP per reservoir — but it cannot be ordered from a catalogue. Injecting steam into a field that calls for chemistry, or polymers where gas is needed, means spending a lot to recover little. Everything therefore starts with a quiet, decisive exercise: screening — matching each method against the measured properties of the reservoir.
This article explains the logic of that grid — the very one we detail on our Enhanced recovery page.
Three families, three logics
EOR methods fall into three families. The chemical route — polymers, then alkali-surfactant-polymer (ASP) — thickens the injection water for a better sweep and lowers interfacial tension to unstick trapped oil. The thermal route — cyclic steam stimulation (CSS) — heats the reservoir to thin a viscous crude. The gas route — water-alternating-gas injection (WAG) — brings gas back into contact with the oil to swell and remobilise it.
Each attacks a different lock: chemistry fights the capillary trap, steam fights viscosity, gas fights the reservoir’s lack of energy. Hence the golden rule: you do not pick a method, you diagnose a field.
The grid, line by line
API gravity and viscosity describe the crude: light and mobile suits gas; moderately heavy suits chemistry; very viscous suits steam. Depth arbitrates between steam and gas: too deep and steam loses its heat on the way down; too shallow and gas cannot be compressed to the point of mixing with the oil. Reservoir temperature bounds the chemical route — beyond a threshold, polymers and surfactants degrade. Permeability, finally, governs polymer injection: the molecule must fit between the grains.
None of these criteria is a verdict on its own. It is their intersection that eliminates dead ends and leaves, for each field, one or two candidate routes — no more.
The Doba sandstones
Applied to the mature fields of the Doba basin, the grid speaks clearly. Crude of 21 to 24° API, shallow sandstones, moderate temperatures: the sweet spot of the chemical route. Better still: the crude’s naturally high acidity — the TAN that complicates refining — becomes an asset, because the injected alkali saponifies those acids and manufactures surfactant in situ. The molecule’s flaw works for recovery.
Steam remains a card to play on the shallowest, most viscous pockets; WAG will wait for a gas source — one of the stakes of the sleeping Sédigui field.
Screening does not say "which method is best" — it says "which one has earned the right to be tested here". It is a filter, not an oracle.
What the grid does not say
Passing the screen is only an entry ticket. There remain laboratory core floods, compatibility with the formation water, the availability of inputs — where Chad holds cards of its own, from Kanem natron to gum arabic — and then a pilot on a few wells before any rollout. And of course the economics: an additional barrel is only worth recovering if it costs less than it sells for — the whole point of our Barrel calculator.
EnerTchad is a company in formation: these methods are study and pilot programmes, dated in our 2030 targets, not processes in operation. But the approach is settled: measure first, choose second, pilot before promising.