Biogeochemical Analyses of Four Crude Oil Samples to Confirm the Presence of Terrestrial-organic Matter, Collected from the Murzuq Basin- Libya

Abstract

The Murzuq Basin, in Southwestern Libya, is one of Libyan’s most productive petroleum basins, with reserves estimated at 23 billion barrels recoverable of hydrocarbon equivalent within giant oil fields. Four crude oil samples collected from A1-NC186, E1-NC101, E2-NC101, H10-NC115 wells from Murzuq Basin, Libya, were suggested for bulk analysis and physical proprieties, alkane distribution and isoprenoids and the hopane, tricyclic terpane and sterane distributions of the oils, to confirm the presence of non-marine organic matter sources and/or any evidence of its existence. The oils show no significant variation in the ratios of the carbon, hydrogen, nitrogen and sulfur content (CHNS) composition. All samples recorded high to very high API° gravity, ranges 33.8 to 40.3; the sulfur values ranged from 0.31 to 0.45%, the wax ratio in crude oils is showing a great variety, E1-NC101and E2-NC101 oils show higher wax content, ranging from 6.1 to 6.7%. Pristine to Phytane ratios (Pr/Ph) range from 1.61 to 2.22 and the Pr/n-C17, Ph/n-C18, n-C17/n-C27 and CPI values determined as indicators of the depositional environment of the crude oils. The data of search confirmed that the crude oils were derived from marine, mixed and terrestrial sediments.

Geochemical Characteristics of Crude Oils From the Sharara‐c Oil Field, Murzuq Basin, Southwestern Libya

“…The interpretations of source rock depositional environment and lithology of the Sharara-C oils analysed in this study agree well with previouslypublished results for oils from this part of the Murzuq Basin (Hodairi and Philp, 2012;El Diasty et al, 2017;Aboglila et al, 2020). They also agree with literature data describing the Tanezzuft "hot" shales, the main source rock for the oils found in this region, as a marine shale rich in clays (Hallett and Clark-Lowes, 2016).…”

“…Ratios of pristane to phytane for the Sharara-C oils (Table 3) indicate derivation from a source rock which was deposited in intermediate (suboxic) conditions (Murray and Boreham, 1992). The pristane/ phytane ratios of the Sharara-C oils analysed in this study agree well with those of previous studies on oils from other Sharara fields in the Concession NC-115, indicating a possible common source for all the oils (Hodairi and Philp, 2012;El Diasty et al, 2017;Aboglila et al, 2020). However, these results which indicate an intermediate (suboxic) environment for the source rock of the oils are not consistent with published data for the Tanezzuft "hot" shale source rock which is interpreted to have been deposited under anoxic conditions (Hallett and Clark-Lowes, 2016 and reference therein).…”

“…In general, the results of this study regarding the maturity of the source rocks of the Sharara-C oils agree well with maturity assessments for source rocks of oils from other Sharara fields (Hodairi and Philp, 2012;El Diasty et al, 2017;Aboglila et al, 2020) which found that the source rocks were medium to highly mature. However, after comparison of the results for the individual maturity parameters of the Sharara-C oils with those of oils from the Sharara-A, -B, and -H fields (Hodairi and Philp, 2012;El Diasty et al, 2017), some differences were noticed.…”

“…In other studies, crude oils from the Sharara-A, -B, and -H fields have been investigated for their biomarker characteristics and stable carbon isotope compositions (Hodairi and Philp, 2012;El Diasty et al, 2017;Aboglila et al, 2019;Aboglila et al, 2020). The results showed that these oils originated from a siliciclastic marine source rock containing mixed aquatic and terrigenous material deposited under weakly reducing to suboxic conditions.…”

“…It should be emphasized that although some parts of Concession NC-115 are well described in the literature, this area has not been fully explored. Crude oils from the A-, B-and H-oils fields have been thoroughly characterized in terms of their organic-geochemical composition (Hodairi and Philp, 2012;El Diasty et al, 2017;Aboglila et al, 2019;Aboglila et al, 2020), and organic geochemical data are also available for core and cutting samples from the A-field (Hodairi and Philp, 2011;El Diasty et al, 2017;El Diasty et al, 2017). However, for other fields in the Concession NC-115 area, little organic geochemical data has been published.…”