Journal of Petroleum Geology最新文献

The Chang 7 member of the Upper Triassic Yanchang Formation is an important source rock in the Ordos Basin, NW China. Previous studies of the unit have in general focused on the relatively deep-water (∼25 m) anoxic, OM-rich lacustrine mudstones which form the main Mesozoic source rock at fields in the south of the basin. However, this paper presents an integrated geochemical investigation of the relatively shallow-water Chang 7 facies in a study area around Jiyuan field in the western part of the basin in order to evaluate its source rock potential. The results show that the Chang 7 source rock in the study area has a high content of Type II OM, and is interpreted to have been deposited in a suboxic-anoxic lacustrine setting with a mixed input of aquatic and terrigenous organic matter. The results of 1D modelling of a well in the study area showed that the Chang 7 member entered the oil generation window from the Middle Jurassic. Oil-oil correlations based on hierarchical cluster analysis and correspondence analysis showed that crude oils generated by deep-water Chang 7 source rocks from wells in the south of the basin can be distinguished from Soxhlet-extracted petroleum from reservoir sandstones in the study area. The compositional differences are inferred to be due to variations in source rock facies compositions. An oil – source rock correlation study showed that the shallower-water Chang 7 source rock in the western part of the basin generated the hydrocarbons in core extracts of reservoir sandstones from wells in this area. The shallow-water Chang 7 facies may therefore constitute an effective oil-prone source rock in the western Ordos Basin.

The recent discovery of surface oil seeps in the Tamerza area in the west-central Gafsa Basin (southern Tunisia) has prompted a re-evaluation of the hydrocarbon potential of the region. In this paper, we report the results of analyses of seep oils by Rock-Eval pyrolysis (n = 6) and gas chromatography – mass spectrometry (n = 4). The goals of the study were to assess the composition of the seep oils, to investigate the relationship between the seep oils and potential source rocks, and to highlight the significance of the seep oils for oil exploration in the region.

In the Tamerza area, surface oil seeps have been recorded in numerous formations ranging between the Upper Cretaceous Abiod Limestone Formation and the lower Miocene Sehib Siltstone Formation. The results of this study showed that all the seep oil samples analysed in general had a similar geochemical fingerprint: for example, Pr/Ph values are lower than 1; a plot of Pr/n-C₁₇ (0.27- 0.36) versus Ph/n-C₁₈ (0.3-0.8) indicates a marine source rock deposited under reducing anoxic conditions; and Ts/(Ts+Tm) ratios indicate that the source rock was thermally mature. Correlation studies suggest that the oils originated from Cenomanian-Turonian shales corresponding to the informally-named Bahloul equivalent formation. Oil expulsion from this source rock at the seep locations is inferred to have ended by middle Miocene time. However the main phase of folding occurred here in the Pliocene – early Quaternary, and the resulting anticlinal folds are not therefore prospective structural traps for hydrocarbons because they developed after migration had already ceased. Stratigraphic traps and salt structures in the region may be of greater exploration interest.

A surface oil seep sample was also recovered from the Quaternary upper Segui Formation at Jebel Orbata in the east of the Gafsa Basin. Analysis of this oil sample showed that it has similar geochemical characteristics to the seep oils from the Tamerza area, but that it appears to have had a much more recent migration history. In the eastern Gafsa Basin, Pliocene – early Quaternary anticlinal structures could therefore constitute effective structural traps charged by the same Bahloul equivalent formation source rock.

Background: : Since its declaration as a global pandemic on March11^th 2020, COVID-19 has had a significant effect on solid-organ transplantation. The aim of this study was to analyze the impact of COVID-19 on Liver transplantation (LT) in United States.

Methods: : We retrospectively analyzed the United Network for Organ Sharing database regarding characteristics of donors, adult-LT recipients, and transplant outcomes during early-COVID period (March 11- September 11, 2020) and compared them to pre-COVID period (March 11 - September 11, 2019).

Results: : Overall, 4% fewer LTs were performed during early-COVID period (4107 vs 4277). Compared to pre-COVID period, transplants performed in early-COVID period were associated with: increase in alcoholic liver disease as most common primary diagnosis (1315 vs 1187, P< 0.01), higher MELD score in the recipients (25 vs 23, P<0.01), lower time on wait-list (52 vs 84 days, P<0.01), higher need for hemodialysis at transplant (9.4 vs 11.1%, P=0.012), longer distance from recipient hospital (131 vs 64 miles, P<0.01) and higher donor risk index (1.65 vs 1.55, P<0.01). Early-COVID period saw increase in rejection episodes before discharge (4.6 vs 3.4%, P=0.023) and lower 90-day graft/patient survival (90.2 vs 95.1 %, P<0.01; 92.2 vs 96.5 %, P<0.01). In multivariable cox-regression analysis, early-COVID period was the independent risk factor for graft failure at 90-days post-transplant (Hazard Ratio 1.77, P<0.01).

Conclusions: : During early-COVID period in United States, overall LT decreased, alcoholic liver disease was primary diagnosis for LT, rate of rejection episodes before discharge was higher and 90-days post-transplant graft survival was lower.

Crude oil reserves in tight Middle and Lower Jurassic reservoirs are of increasing exploration interest in the central Sichuan Basin, SW China. However, the origin of these “tight oils” is poorly understood. In this study, sixteen samples of light oils/condensates from tight Middle and Lower Jurassic reservoir rocks were analysed using gas chromatography (GC) and isotope ratio mass spectrometry to investigate the oils’ origin and to classify them into genetic families. The tight oils can be divided into two families. Family I oils occur in the Gongshanmiao oilfield where reservoir units comprise the Da'anzhai Member of the Lower Jurassic Ziliujing Formation, the Lower Jurassic Lianggaoshan Formation, and the First Member of the Middle Jurassic Shaximiao Formation. Family I oils are characterized by relatively low values of the methylcyclohexane (MCH) and cyclohexane (CH) indexes, low values of Mango's parameter K₂ for light hydrocarbon composition, and relatively negative δ¹³C values ranging from -30.8‰ to -28.9‰. Family I oils are inferred to be self-sourced by lacustrine shales in the Da'anzhai Member and the Lianggaoshan Formation in the study area, both of which are rich in sapropelic organic matter. These source rocks also charged reservoirs in the First Member of the Shaximiao Formation. By contrast, the newly discovered Family II oils, which occur at the Jinhua oilfield and the as-yet undeveloped Qiulin and Bajiaochang structures, are reservoired in the Second Member of Shaximiao Formation. Family II oils have higher values of the MCH index, CH index and Mango's K₂ parameter, and δ¹³C values varying from -27.5‰ to -25.4‰. These oils have similar light hydrocarbon compositions and δ¹³C values to oils derived from source rocks in the Upper Triassic Xujiahe Formation which contain dominantly humic organic matter. Family II oils are therefore inferred to be derived from the coaly mudstones in the Xujiahe Formation.

The different compositions of the tight oils in the First and Second Members of the Shaximiao Formation appear to be controlled by the distribution and thickness of source rocks in the study area. Thus, the Gongshanmiao oilfield where Family I oils occur in the First Member is close to the depocentre of source rocks in the Da'anzhai Member and Lianggaoshan Formation. These source rocks are inferred to have charged the First Member reservoirs which may also be present in nearby oil- and gas-bearing structures such as Nanchong and Yingshan. By contrast, Family II oils occur in tight reservoirs in the Second Member in areas with thick successions of Upper Triassic Xujiahe Formation mudstone source rocks, such as the Jinhua oilfield. In areas where both source rocks are present such as the Zhongtaishan and Lianchi oilfields, Shaximiao Formation reservoirs appear to contain both Family I and Family II oils.