Geochemistry and modification of oilfield brines in surface pits in Northern Kuwait

Oilfield brines (produced water) are produced as a waste product daily at the gathering centers (GCs) in Kuwait oilfields. The geochemical evolution of the water produced at the GC (fresh brine) to stagnant pit water (evaporate) has been investigated in the northern fields of Kuwait, and a model is presented showing time-dependent variations. Kuwait oilfield brines are globally similar to others in other large sedimentary basins (USA, Canada), but modifications have occurred due to seawater injection practices performed episodically during the oil extraction process. Brine water chemistry changes from generally average brine chemistry (based on cations and anions) to saturated mixture of seawater, oilfield brine, and anthropogenic chemical pollutants. The objective of this study was to harmonize the database of brine waters in terms of regional identity by comparison with oilfield brines elsewhere, identify water–rock interaction, and statistically treat daily recordings from the pits in order to identify injection peaks and troughs. Laboratory analysis of major and minor cations and anions from the Rawdatayn samples gave the following concentration ranges in parts per million (ppm): (Na + , 11,698–203,977), (Ca 2+ , 2,216–98,514), (Mg 2+ , 1,602–28,885), (K + , 1,528–16,573), (Sr 2+ , 70–502), (Ba 2+ , 0.01–18.04), (Fe 2+ , 0.01–8.93), (Li + , 0.09–6.48), (Si 2+ , 0.00–13.18), (B 3+ , 0.05–37.45), (SO 4 2+ , 330–3100). For the Sabriyah oilfield samples, the major and minor cations and anions concentration ranges in ppm are: (Na + , 9,807–274,947), (Ca 2+ , 2,555–77,992), (Mg 2+ , 1,415–28,183), (K + , 764–19,201), (Sr 2+ , 77.84–641), (Ba 2+ , 0.15–6.76), (Fe 2+ , 0.016–38.88), (Li + , 0.05–6.83), (Si 2+ , 0.0195–16.84), (B 3+ , 7.17–55.33), (SO 4 2+ , 44,812–135,264). The stable isotopic analysis of five samples indicates normal trends in oxygen and hydrogen isotopes that classify the waters as “connate” which follow an evaporation trend. Carbon isotopic signatures are normal for hydrocarbon fields and average out around GC15, δ 18 O‰ = 1.4, δD‰ = −10, δ 13 C‰ = −3.6; while for GC23, δ 18 O‰ = 2.3, δD‰ = −4, δ 13 C‰ = −2.5; for GC25, δ 18 O‰ = −2.0, δD‰ = −14, δ 13 C‰ = −4.6; for pit1, δ 18 O‰ = 2.3, δD‰ = −5, δ 13 C‰ = −18.3; and for pit 2, δ 18 O‰ = 2.5, δD‰ = −4, δ 13 C‰ = −17.8. Carbon isotope average values for all brine samples from the GCs is = −56 which falls within normal hydrocarbon formation water category. Data spikes coincide with injection