Preliminary geochemical characterization of saline formation water from Miocene reservoirs, offshore Niger Delta

Abstract

The Niger Delta is one of the most prolific hydrocarbon provinces in the world, but information on basinal hydrogeology is scanty. Oilfield brines from nine producer wells in the Miocene reservoirs (2,472.25–3,532.48 m.b.s.l.), offshore Niger Delta, have been investigated along with two seawater samples to understand their hydrogeochemical characteristics in relation to the host rock mineralogy. Chemical analysis revealed that the waters are slightly alkaline and can be generally classified as saline water of the Na–Cl type based on their total dissolved solids (TDS). On the basis of bicarbonate, chloride, and sulphate ions, they are shown to be of connate origin. Relative abundance of major ions is in the following order: Na > Ca > Mg > K and Cl > HCO 3 > SO 4 . Saturation indices (SI) of selected mineral phases calculated using PHREEQC indicate that the dissolution of iron oxide and carbonate minerals may contribute major ions in the formation water. The preponderance of alkali elements suggests the presence of feldspars, which could have resulted from sediments through which the water flows. An inverse relationship is observed between the resistivity of formation water and its TDS, which could be used to calculate resistivity values of formation waters in the area if the TDS contributions are known. Chemical data suggest that the formation waters were derived from seawater, dominantly altered by reverse ion-exchange processes and subsequently by water-rock interactions. Multivariate statistical analyses (correlation and factor analysis) indicate multiple sources of enrichment of ions in the formation waters.

Evaluation of modified cashew nutshell liquid as natural surfactants for chemical flooding in sandstone oil reservoirs

“…The brine contained varying concentrations of sodium chloride, calcium, and magnesium chloride with a total dissolved solids (TDS) of 30,000 ppm with 5000 mg/l being total concentrations of calcium and magnesium chloride (divalent ions). The composition of the brines as presented in Table 2 was formulated based on the report of [5] which noted that the TDS of most formation water in Niger Delta reservoirs vary between 14,537 and 31,761 ppm with its composition in the order of Na > Ca > Mg > K. The varied concentrations were mixed in a beaker containing one litre of distilled water, and this was placed on a magnetic stirrer at a temperature of 27 ˚C for 10 min. The solution was allowed to settle and then filtered using a filter paper.…”

Analysis of nutrient loads, heavy metals and physicochemical properties of wastewater, wetland grass, and papaya samples: Gondar Malt factory, Ethiopia with global implication

“…The possible reason might be due to their soluble salts in barley of malt and dust particles of the raw material. The dissolved solids in natural wastewater are mostly calcium carbonates, magnesium carbonates, sodium carbonates, potassium carbonates, iron carbonates, manganese carbonates, etc [9] .…”

Indication of Formation Water Geochemistry for Hydrocarbon Preservation: New Applications of Machine Learning in Tight Sandstone Gas Reservoirs

“…The concentration of SO 4 2– is related to the intensity of desulfurization and redox conditions, and desulfurization bacteria play a decisive role in controlling the concentration of SO 4 2– in formation water . In deep oil and gas reservoirs, sulfates are converted into sulfides by desulfurizing bacteria in water, so the content of SO 4 2– decreases and the desulfurization coefficient decreases.…”

“…The concentration of SO 4 2– is related to the intensity of desulfurization and redox conditions, and desulfurization bacteria play a decisive role in controlling the concentration of SO 4 2– in formation water. 49 In deep oil and gas reservoirs, sulfates are converted into sulfides by desulfurizing bacteria in water, so the content of SO 4 2– decreases and the desulfurization coefficient decreases. Theoretically, the smaller the desulfurization coefficient is, the better is the formation sealing, indicating a higher degree of formation water reduction, which is more conducive to the gas accumulation.…”