Hydrochemistry as a tool for interpreting brine origin and chemical equilibrium in oilfields: Zubair reservoir southern Iraq case study

Abstract

The oil reservoir brines are very common geological fluids coexisting with hydrocarbons. The chemistry of brines is a powerful tool for determining the brine evolution and its origin, constraining fluid flow at the basin and predicting reservoir scales. This study targeted the Zubair brines in seven oilfields and investigated the geochemical evolution of brine compositions. The composition of the Zubair brine is characterized by the high average of TDS (219,408 mg/l). The contribution of cations as epm% are Na (73.7), Ca (17.32), Mg (7.45), and K (1.27), while anions contribute as Cl (99.6), SO 4 (0.23), HCO 3 (0.08), and CO 3 (0.005). The Zubair brines are of Na-Ca-chloride type, whereas sodium content is 6.3 times greater than seawater; Ca and Mg contents are thirty-four and three times greater, respectively, while Cl is seven times greater. The SO 4 ion is depleted to 0.16, due to a biodegradation. The salinity of the Zubair brine is six times more than that of seawater. The Zubair brines are characterized by an acidic pH (5.24-5.68) with a specific gravity of 1.1436, hydrocarbon saturation in pore spaces of 39%, and water saturation of 61%. The mineral saturation model indicates that Zubair brines are unsaturated. The predicted hypothetical salts are NaCl (76%), CaCl 2 (15%), and MgCl 2 (7.5%). The salts Ca(HCO 3) 2 , CaSO 4 , and KCl together form only 1.6%. The Zubair brines are characterized by Cl/Br (305) in average, greater than that of seawater (289) confirming the fluids (brines and hydrocarbons) migrated upwards from Sargelu Formation to Zubair reservoir through fractures and cracks in Gotnia Formation.

Effect of Water Flooding on Oil Reservoir Permeability: Saturation Index Prediction Model for Giant Oil Reservoirs, Southern Iraq

“…The contact between pore fluids and pore-lining minerals that exist in pore spaces of a petroleum reservoir may lead to formation damage that happens due to rock-fluid interactions (Awadh et al, 2019). Pore-lining minerals do not enhance permeability.…”

“…Carbonate scales include calcite and aragonite formed by the combination of a calcium ion with a carbonate ion (Patton, 1977). Four main factors influence the calcium carbonate scale build-up (Awadh et al, 2019), namely partial pressure of CO 2 , pH, temperature and total dissolved salt. The CaCO 3 can be precipitated in an alkaline pH as:…”

Sequence Stratigraphy and Depositional Environment of the Zubair Formation in Rumaila Oilfields, Southern Iraq: Microfacies and Geochemistry

“…The Zubair Formation became very important and considered the most promising oil-bearing rock unit since 1948 when the international oil company (IOC) had drilled the first oil well in southern Iraq. The Zubair, Ratawi and Shuaiba Formations are part of the Thamama Group and belongs to the Late Barremian-Aptian sedimentary cycles in which, the Zubair units have heterogeneity of organic matter content that eventually affect permeability (Awadh, 2018;Awadh et al, 2019). The studied region is located in the Mesopotamian zone's southernmost unit within the Zubair subzone (Fig.…”

Structural Interpretation of Yamama and Naokelekan Formations in Tuba Oil Field Using 2D Seismic Data

“…There is through its high analytical capacity and ability to give a close picture to the subsurface geological situation, delineation the type of the oil traps (structural, stratigraphic) with a good estimation of the reservoir characterizations (porosity, lithofacies, fluid content and water saturation) (Telford et al, 1990;Lines and Newrick, 2004;Al-Sadi, 2017;Awadh et al, 2018;Awadh et al, 2019;Awadeesian et al, 2019). The main steps of the seismic reflection method are the acquisition field seismic data, processing then interpretation to get an image, which closes, to the real subsurface geology.…”