00075 Hydrothermal petroleum in the sediments of the Andaman Backarc Basin, Indian Ocean

02 Formation as a major source to the known oil discoveries in the study area, the contribution of the Enping Formation source to traps in the Huizhou Sag and surrounding area cannot be ignored. There is clear evidence for the recharge of Enping Formation derived oils into earlybiodegraded oil accumulations to form light oil accumulations. 04/00074 Geochemistry, grouping and origins of crude oils in the Western Pearl River Mouth Basin, offshore South China Sea Huang, B. et al. Organic Geochemistry, 2003, 34, (7), 99331008. Thirty-seven crude oils and 20 source rocks were selected for detailed molecular geochemical and isotopic analyses in order to establish the genetic relationships between the discovered oils and various petroleum source facies in the Western Pearl River Basin, offshore South China Sea. Four groups of oils were identified. The Group I oils, distributed in the southwestern WC19-1 field of Wenchang B sag, are characterized by high abundance of 4-methyl steranes relative to regular steranes, low abundance of bicadinanes and high 6i3C values, showing good correlation with the medium-deep lacustrine source facies in the Wenchang Formation. The Group II oils represent the majority of the discovered oil reserves in the study area, including those from the Qionghai uplift and the northeast block of the WC19-1 oil field. These oils have moderate concentrations of Caa 4-methylsteranes, abundant bicadinanes and low 613C values, and correlate well with the shallow lake source facies of the Wenchang Formation in the Wenchang B and A sags. The group III oils, found in the Wenchang A sag and surrounding areas, are devoid of Csa 4-methylsteranes, with abundant bicadinanes and similar Si3C values to those of the Group II oils. These characteristics show close affinity with the coal-bearing sequence in the Enping Formation, thus suggesting a coaly source for these oils. The Group IV oils, found only in the WC8-3 field, display intermediate chemical compositions between the Group II and Group III oils, most likely from mixed sources in the Wenchang A sag. These oil-source genetic relationships suggest dominantly short distance oil migration and thus strong source facies controls on the geographic distribution of oil and gas fields within the Western Pearl River Mouth Basin. 04/00075 Hydrothermal petroleum in the sediments of the Andaman Backarc Basin, Indian Ocean Venkatesan, M. I. et al. Applied Geochemistry, 2003, 18, (6), 845-861. Recent sediments of the Andaman Backarc Basin, Indian Ocean, between the Andaman Nicobar islands and the Malay Peninsula have been analysed for biomarker lipids. Three cores were selected: one each from the fault zone in a deep basin (a graben between two fault systems), another from a location adjacent to the fault, and the third from the topographic high in the rift valley. The molecular composition of the lipid classes (n-alkanes, isoprenoids, alkylbenzenes, alkylcyclohexanes, hopanoids, polycyclic aromatic hydrocarbons, steranes, alcohols, sterols and fatty acids) was examined by gas chromatography (GC) and GC/mass spectrometry to understand the nature and source of the hydrocarbons present and the processes of maturation of organic matter. The data show that the hydrocarbons are of hydrothermal origin, derived from thermal alteration of sedimentary organic matter, consisting of a mixture predominantly of marine-derived components with some terrestrial inputs. Normal alcohols and fatty acids also corroborate the distribution of rz-alkanes. The distribution profiles and various parameters computed from the concentration of the target compounds suggest that oxidative reactions and microbial degradation in this environment are insignificant. Triterpane and PAH compositions indicate that the thermal maturity of the bitumen in the samples is comparable to or lower than that found at other hydrothermal regions such as the Northern Juan de Fuca Ridge, Guaymas Basin and Escanaba Trough. 04/00076 Improving flow properties of heavy crude petroleum Khan, M. R. et al. PCT Int. Appl. WO 03 35,802 (Cl. ClOG9/00), 1 May 2003, Appl. 2001/US50~791. The flow properties of crude petroleum having an API gravity of -6 to 12 are improved by heating the crude petroleum to a temperature of x35-200’ and, in the presence of a suitable viscosity reducing additive, shearing the heated crude petroleum with a high shearing force sufficient to reduce the viscosity of the crude petroleum to a range of x250 cP (9 to =lOOO cP). Suitable viscosity reducing additives include gasoline, naphtha, butanol, petroleum ether, diesel fuel, citrus oil based cleansers and degreasers, and mixtures thereof. 04100077 Influence of biodegradation on carbazole and benzocarbazole distributions in oil columns from the Liaohe basin, NE China Huang, H. et al. Organic Geochemistry, 2003, 34, (7), 951-969.

Liquid

fuels

(sources,

properties,

recovery)

Alkylcarbazoles and benrocarbazoles in petroleum reservoir core extracts isolated from several oil columns within the Lengdong oilfield, Liaohe basin, China were studied to investigate their occurrence and the effect of biodegradation on their concentrations and distributions. Bulk petroleum composition and molecular data indicate the occurrence of systematic biodegradation gradients within the oil columns, the extent of biodegradation ranging from light (level 1) to moderate (level 4-5) in Es3 columns, and from moderate (level 5) to heavy (level 8) in Es1 columns. Whereas carbazoles and benzocarbazoles can be useful as migration markers in certain geological situations, the results presented here indicate that biodegradation also plays a significant role in controlling the distribution of carbazole compounds in reservoired oils. Alkylcarbazoles are generally regarded as resistant to biodegradation at low to moderate levels of biodegradation but at biodegradation levels greater than level 4 they may be microbially altered in a way similar to that observed for aliphatic and aromatic hydrocarbons. The concentrations of carbazole compounds in the oils increase slightly during the early stages of biodegradation and then sharply decrease after level 4, when preferential depletion of alkylated carbazoles compared to benzocarbazoles and dibenzocarbazoles or naphthocarbazoles is observed. The susceptibility of alkylated carbazole isomers to biodegradation decreases with increasing carbon number of the alkyl substituents. Furthermore, nitrogen (N-H) shielded or partially shielded compounds substituted in the one and/or eight positions seem more susceptible to biodegradation than their nitrogen-exposed counterparts. For example, biodegradation resulted in the preferential removal of l-methylcarbazole relative to the other methylcarbazole isomers and among the dimethylcarbazoles; 1,8-dimethylcarbazole seems more susceptible to biodegradation than other isomers, even though some exceptions do occur in the sample set. The benzocarbazole ratio decreased with increasing degree of biodegradation, Benzo[b]carbazole has the highest apparent ability to resist biodegradation among the benzocarbazole isomers.

04100078 Initial stages of asphaltene aggregation in dilute crude oil solutions: studies of viscosity and NMR relaxation Evdokimov, I. N. et al. Fuel, 2003, 82. (7), 817-823. In crude oil-toluene solutions dynamic viscosity 17 and spin-spin relaxation time T, were measured as functions of asphaltene concentration C in the range of lo-300 mg/l. The results were supplemented by studies of optical absorption. Extrema in the measured concentration dependencies are attributed to a transient predominance of specific asphaltene aggregates-from dimers to stacked molecular nanoclusters (MNCs) of four monomers. The strikingly nonideal properties of solutions with C below 150-170 mg/l are attributed to the strong interactions between asphaltene species. At higher C the solution properties are evidently determined by the weaker interacting MNCs and the concentration effects are closer to those in ideal fluid mixtures. The observed re-entrant n(T,) behaviour in asphaltene solutions hypothetically has the same origin as in supercooled or demixing molecular systems, where anomalous structural and dynamical features are often explained by emerging heterogeneity due to transient spontaneous clustering.

04/00079 Local rock mechanical drilling performance in fractured field Stjern, G. et al. Journal oj’Petroleurw (3-4),

knowledge formations Science

improves at the Heidrun

and Engineering,

2003, 38,

83-96.

Despite the use of inhibitive water-based mud (KC]), high pump rates to obtain good hole cleaning and relatively high mudweight, problems with cavings, pack-offs and lost circulation persisted when drilling Tertiary shale formations in the Heidrun field offshore Mid-Norway. A study was therefore initiated, including extensive data collection (logging and coring of the shale) and subsequent core testing, data analysis and evaluation of field experience. The study showed that the major problem zone was not the low-density zone as anticipated. However, the core revealed a fractured and crushed zone, which was eventually found to be the main source of the problem. The study has resulted in a new strategy. An improved borehole stability model has been established, and the mud and operational strategies have been revised. The mudweight has been reduced, the salt content of the mud has been reduced and good hole cleaning is obtained through a lowviscosity mud, which is kept close to turbulent flow. Furthermore, if possible, wells are now planned without steering in these formations. If steering cannot be omitted, 3-D rotary steerable systems are utilized. An economic evaluation of the study was also performed, showing a substantial benefit/cost ratio. So far, the cost reduction for an average well is close to 20 MNOK (ca. US$2.5 million). With more than 50 wells left to drill in the field, the potential for cost-saving is large. Additionally, there is a huge and non-quantified effect from accelerated production. Fuel

and

Energy

Abstracts

January

2694

I I