Petroleum geochemistry of oil samples from shallow boreholes at Sakran site,western Iraq

Findings of the oil source affinity for oil sample collected from shallow borehole already drilled for ground water purposes at the Sakran area, NE Haditha city, western Iraq, is performed in this study by biomarker studies with addition to the analysis of gravity map. Petroleum geochemistry study is carried out on oil sample. The terpane and sterane biomarker distributions, as well as the stable isotope values, are used for determining the validity of oil to correlate its source. The results showed that the oil belongs to the Jurassic age, with high sulfur content (2.75 %) and value of C28/C29 up to 0.75. The tricyclic terpanes values as well as hopanes indicated a source rock affinity of carbonates, whereas the pristine/phytane ratio indicated marine algal source of kerogen type II. All these information could confirm that the source rock affinity was the Sargelu Formation (Jurassic), in which their age’s equivalent to the source in East Baghdad Oil Field and Tikrit Oil Field, with a difference from the oil family near the Akkas field, located to the west of the area. Chemical analyses of water sample collected from the borehole showed the following results: TDS?=?12,700 mg/l, EC?=?215,900 μs/cm, pH?=?6.8, DO?=?28 mg/l, and temperature?=?24 °C. Hydrochemical functions such as rNa/rCl (<1), (rNa–rCl)/rSO₄ (<0) and rSO₄/rCl (<1) indicate that the water is of marine origin, partially mixed with meteoric water. Analysis of the gravity map revealed two anomalous areas; the western one represents large anomaly with EW trend similar to the Anah graben to the north. The second one consists of many anomalies trending N–NW direction. The main local anomaly is identical with the seeps from the drilled borehole covering large area. The boundaries and trends of the main geological structures have been defined by gradient analysis procedure to the gravity data. The closed gravity anomalies with their large extensions reflect the importance of the results for further studies and promising area for oil reservoirs.