Enhanced oil recovery rises or falls on three unglamorous steps: fine filtration, near-zero oxygen, and a disciplined biocide program. Field and lab data show microns of solids and tens of ppb oxygen decide injectivity, corrosion, and uptime.
In modern waterfloods, “all suspended solids” must be removed before injection, dissolved oxygen has to be driven to near zero, and microbes kept nominally sterile. That is not rhetoric; it’s backed by experiments, models, and standards such as NACE SP0499–2012.
Surface waters can carry tens to thousands of milligrams per liter (mg/L) of suspended solids — rivers: 100–1,000 mg/L; deep seawater: ~5–50 mg/L (SPE PetroWiki). Even tiny particulates plug pores: models show increasing injected total suspended solids (TSS) from 10 mg/L to 100 mg/L doubled the near‑well damage radius over three years and cut the “safe” damage time by ~30% (ResearchGate).
Corrosion risk is equally unforgiving. Seawater injection guidelines target dissolved oxygen (DO) in the tens of parts per billion (ppb), with NACE SP0499–2012 recommending ≤50 ppb to achieve a 5–7‑year tubing life (ResearchGate). And microbes — notably sulfate‑reducing bacteria (SRB) — routinely reach >10^3–10^6 cells/mL in produced water versus <1/L in surface seawater (MDPI), driving microbially influenced corrosion (MIC) that accounts for ~20–50% of corrosion‑related costs (MDPI).
Suspended solids control and filtration targets
Industry practice uses multi‑stage filtration: hydrocyclones or strainers remove >50 μm solids, followed by media or cartridge filters down to a few microns. Designs often aim for turbidity <1 NTU (nephelometric turbidity units) and TSS in single‑digit mg/L (SPE PetroWiki; ResearchGate). Minerals (silica, iron, clays) and organics in particulates are frequent plugging agents (SPE PetroWiki; ResearchGate).
Coarse capture typically starts with 50–250 μm devices; in high‑pressure service, operators pair fine elements with industrial strainers and steel filter housings. For depth filtration, dual‑media beds such as sand and silica media remove ~5–10 μm particles, with polishing via cartridge filters at ~5–10 μm or membranes. In some designs, ultrafiltration/μm membranes are added as a “polishing” step (SPE PetroWiki; ResearchGate), where packaged ultrafiltration systems serve as pretreatment to membrane trains.
The stakes are visible in the near‑wellbore. Modeling shows most particle retention occurs within <5 meters of the wellbore (ResearchGate). An Indonesian lab study found that injecting water containing 25% produced‑water (with high bacteria/solids) cut rock permeability by ~80%; adding an 11 μm filter and 2000 ppm biocide halved the damage to a 47% permeability loss (LEMIGAS; LEMIGAS). Without polishing filtration, produced‑water solids (>10 μm) caused near‑complete injectivity loss at only 25% dilution (LEMIGAS).
Typical solids‑removal trains include hydrocyclones, platelet filters, and cartridge filters (SPE PetroWiki). Operators track filter differential pressure and replace cartridges regularly; the cost of fine filtration is justified by avoiding formation permeability loss or well kill (ResearchGate). In short, “all suspended solids” must be removed before injection; incremental treatment costs are far cheaper than re‑drilling or downhole remediation of plugged wells.
Oxygen control and deaeration standards
Injected water must be nearly oxygen‑free to prevent corrosion of carbon steel. Targets are in the tens of ppb — operators monitor DO (dissolved oxygen) with sensitive analyzers and hold 10–50 ppb (0.01–0.05 mg/L), with NACE SP0499–2012 recommending ≤50 ppb for a 5–7‑year tubing life (ResearchGate). Practically, O₂ is driven to ≪0.05 mg/L via vacuum degassers or oxygen scavengers (ResearchGate).
One experiment underscores the effect: degassing freshwater from ~6–9 mg/L down to ~0.5 mg/L O₂ dropped pipe corrosion rates from 3–18 mm/yr to <1.5 mm/yr, and with stronger scavenging to near 0.1 mm/yr (University of Baghdad repository). For chemical polishing, upstream dosing of trace sulfate‑based scavenger is common; facilities deploy oxygen/H₂S scavengers with accurate dosing pumps. Injecting inert gases like N₂ or ammonia can also strip O₂ (ResearchGate).
The penalty for missing these targets is severe: even a few ppm O₂ can shift carbon‑steel attack from <0.5 mm/yr to several mm/yr (University of Baghdad repository). Oxygen also promotes bio‑crust formation; in practice, a rise in injection‑line pressure or corrosion‑product fouling often flags O₂ breakthrough (ResearchGate). Effective deaeration — vacuum towers, membrane degassers, or chemical scavengers — extends equipment life by years; NACE predicts 5–7 years with <50 ppb O₂ (ResearchGate), and the cost of O₂ removal is minor compared to replacing corroded tubing or downhole failure.
Microbial control and biocide dosing
Produced water is nutrient‑rich, supporting iron‑, sulfur‑, and slime‑forming microbes. Unchecked, these create biofilms, generate H₂S, and induce severe biocorrosion or pore plugging. Counts often exceed 10^3–10^6 SRB cells/mL in produced water versus <1/L in surface seawater (MDPI), and MIC can account for ~20–50% of corrosion‑related costs (MDPI).
Reinjection schemes apply continuous or pulse biocide dosing — glutaraldehyde, THPS, quaternary amines, or oxidizers (MDPI). A formal target is “nominally sterile” injection water: operators aim for very low CFU (colony‑forming units, e.g., <10^2/mL) and H₂S ≪1 ppm while maintaining free‑biocide residuals often 5–50 mg/L after dilution. In situ nitrate dosing can outcompete SRB; in one field, nitrate cut SRB counts 1000× and halved corrosion rates (MDPI). Programs commonly deploy broad‑spectrum biocides with controlled injection via dosing pumps, and — where oxidizers are preferred — on‑site generation through electrochlorination.
The permeability stakes mirror the solids story: in an Indonesian case, adding 2000 ppm biocide and sub‑11 μm filtration cut microbial plugging dramatically — permeability loss fell from 80% to 47% (LEMIGAS; LEMIGAS). Untreated microbes lead to souring (H₂S rises) and metal failure; bacteria‑coated sands or black slime can irrevocably foul reservoirs. Surges in H₂S or sulfate often signal biogrowth, and entire injection strings have failed due to SRB; suppressing SRB can reduce corrosion by ~50% (MDPI; MDPI).
Operationally, a robust biocide program safeguards injectivity and infrastructure. Periodic “shock” sulfur‑residual or continuous ultra‑low‑level prevent colonization; the data‑driven result is fewer H₂S shutdowns and extended pump life. Investing in biocide — and confirming efficacy via regular bacteria counts/H₂S levels — provides high ROI in reliability (LEMIGAS).
Operating outcomes and economic rationale
Well‑designed filtration yields stable injection rates; unfiltered solids cause rapid pressure rise and filter‑cake formation (ResearchGate). In practice, operators track filter differentials and replace cartridges; pairing fine elements with rugged steel housings supports high‑pressure duty. The cost of fine filtration is justified by avoiding formation permeability loss or a well kill.
For corrosion, effective deaeration — down to ≲50 ppb O₂ — extends tubing life by 5–7 years under NACE SP0499–2012 guidance (ResearchGate), and the cost of oxygen removal is minor compared to replacing corroded strings (University of Baghdad repository). These practices are now standard and underpin the economics of large‑scale water reinjection projects (ResearchGate).
Summary of requirements and sources
Fine filtration to sub‑10 μm — often <5 μm — is mandatory to protect reservoir permeability (SPE PetroWiki; ResearchGate). Dissolved O₂ must be near zero (≲50 ppb) to prevent corrosion (ResearchGate; ResearchGate). Biocide (and/or nitrate) is routinely applied to suppress microbial growth (ResearchGate; LEMIGAS), with operators in Indonesia and globally drawing on SPE, NACE, and peer‑reviewed literature — including local SKK‑Migas experience (ResearchGate).
