Variability of petroleum inclusions in vein, fossil and vug cements—a geochemical study in the Barrandian Basin (Lower Palaeozoic, Czech Republic)

Although no commercial oil or gas occurrences have been found in the Barrandian Basin, residual oils and petroleum inclusions give evidence about the petroleum history of this Lower Palaeozoic Basin. Petroleum inclusions are hosted in six generations of calcite and quartz cements that can be attributed to different stages of a basinal cycle and associated diagenetic events. They were analysed using an on-line crushing and an off-line crush-and-leach approach. Five different groups (PI-A to PI-E) and intermediate mixtures (PI-M) could be differentiated based on the relative distribution of n-alkanes. All oils had a calculated aromatic maturity R_c ranging between 0.9 and 1.6%. PI-A shows a molecular weight maximum in the range of n-C_8–11 with a constant attenuation towards higher carbon numbered n-alkanes. This distribution is interpreted as the pristine precursor oil for other petroleum inclusion groups. PI-B has a maximum weight abundance at n-C_15–20. The genetic relationship between PI-B and PI-A can tentatively be explained by mixing effects or by gas stripping. PI-C is bimodal and characterised by a molecular weight maximum at n-C_32–34, and also a molecular weight maximum at n-C_15–20 similar to that of group PI-B. PI-D shows a normally distributed molecular weight maximum in the range n-C_25–28 and is interpreted as a wax precipitate from ascending gas saturated in n-alkanes. PI-E contains predominantly gaseous compounds with only a few higher hydrocarbons. Thompson's aromaticity values are elevated for condensates of group PI-E, and also for group PI-C that is dominated by long-chained n-alkanes. This gives evidence that fault-bound petroleum migration in the Barrandian Basin was associated with evaporative fractionation for group PI-C and PI-E. Samples of group PI-E yielded gas-range compounds only, and all come from a last generation of vein-filling whitish calcite that was formed in a late uplift phase of the basin. For other petroleum inclusion groups, only a vague preferential occurrence in specific mineralisation phases or stratigraphic intervals of the host rock has been found. This reflects the predominance of fracture-bound migration in the Barrandian Basin. Aromatic maturity values also showed no correlation between either crystal type or PI-group. In six of the investigated petroleum inclusion samples alk-1-enes are present. These terminal olefins are interpreted to be the result of the natural pyrolysis of petroleum due to the intrusion of volcanic dykes or hydrothermal processes. An artificial generation of olefins during sample work-up and analysis is unlikely. The preservation of alk-1-enes from Palaeozoic times was possible due to the protecting environment of petroleum inclusions.     

Accumulation Mechanisms and Evolution History of the Giant Puguang Gas Field, Sichuan Basin, China

Solid bitumens were found throughout the carbonate reservoirs in the Puguang gas field,the largest gas field SO far found in marine carbonates in China,confirming that the Puguang gas field evolved from a paleo-oil reservoir.The fluid conduit system at the time of intensive oil accumulation in the field Was reconstructed,and petroleum migration pathways were modeled using a 3-D model and traced by geochemical parameters.The forward modeling and inversion tracing coincided with each other and both indicated that oils accumulated in the Puguang-Dongyuezhai structure originated from a generative kitchen to the northwest of the Puguang gas field.The deposition of organic-rich Upper Permian source rocks dominated by sapropelic organic matter in the Northeast Sichuan Basin, the development of fluid conduit system that was vertically near-source rock and laterally near-generative kitchen,and the focusing of oils originated from a large area of the generative kitchen,were the three requirements for the formation of the giant paleo-oil reservoir from which the giant Puguang gas field evolved.The Puguang gas field had experienced a three-stage evolution.The post-accumulation processes,especially the organic-inorganic interaction in the hydrocarbon-water-rock system,had not only profoundly altered the composition and characteristics of the petroleum fluids,but also obviously changed the physicochemical conditions in the reservoir and resulted in complicated precipitation and solution of carbonate minerals.     

Accumulation Mechanisms and Evolution History of the Giant Puguang Gas Field,Sichuan Basin,China

Solid bitumens were found throughout the carbonate reservoirs in the Puguang gas field, the largest gas field so far found in marine carbonates in China, confirming that the Puguang gas field evolved from a paleo-oil reservoir. The fluid conduit system at the time of intensive oil accumulation in the field was reconstructed, and petroleum migration pathways were modeled using a 3-D model and traced by geochemical parameters. The forward modeling and inversion tracing coincided with each other and both indicated that oils accumulated in the Puguang-Dongyuezhai structure originated from a generative kitchen to the northwest of the Puguang gas field. The deposition of organic-rich Upper Permian source rocks dominated by sapropelic organic matter in the Northeast Sichuan Basin, the development of fluid conduit system that was vertically near-source rock and laterally near-generative kitchen, and the focusing of oils originated from a large area of the generative kitchen, were the three requirements for the formation of the giant paleo-oil reservoir from which the giant Puguang gas field evolved. The Puguang gas field had experienced a three-stage evolution. The post-accumulation processes, especially the organic-inorganic interaction in the hydrocarbon-water-rock system, had not only profoundly altered the composition and characteristics of the petroleum fluids, but also obviously changed the physicochemical conditions in the reservoir and resulted in complicated precipitation and solution of carbonate minerals.     

叠合盆地油气富集/贫化机理的思考

对四川盆地和准噶尔盆地2个油气藏的成藏机理和成藏模式进行了解剖,以此为基础,探讨了叠合盆地油气成藏与分布的控制因素。从油气成藏的角度,叠合盆地的主要特征是多生烃凹陷与多层位源岩、多元(干酪根、储层和源岩沥青、已聚集油气)、多期生烃、输导体系和能量场的时空差异性和复杂的聚集后过程。多期构造控制下的成藏过程的叠加方式控制油气的富集和贫化,多灶、多源汇聚性叠加和同源多期继承性、强化性叠加是叠合盆地油气富集的重要机制,而多灶、多源离散性叠加、同源多期调整改造性叠加可导致油气的贫化。     

Supergene transformed naphthides: Peculiarities of trace-element composition

Available data on the transformation of naphthides (oils and bitumens) in various petroleum basins (PB) during supergene processes were generalized to reveal their characteristic features for more accurate prediction of pool preservation and commercial quality of oils as hydrocarbon raw material enriched in economically significant toxic metals. Using petroleum basins of the United States, Canada, Brazil, Venezuela, Nigeria, Russia, Kazakhstan, and Turkmenia as examples, itwas demonstrated that trace-element concentrations and ratios as well as metalloporphyrin complexes (MPC), including vanadium (Vp) and nickel (Nip) ones, which are associated with heavy resinous-asphaltene components of oils, serve as geochemical criteria of supergene transformed fluids. During supergenesis, oils show differential enrichment in metals. Considerable enrichment in V, Ni, Co, Mo, Cr, and other trace elements as well as MPC were found in oils generated by sapropel organic matter (OM) and initially enriched in metals (deposits of the South Tatar arch of the Volga-Urals, Buzachi arch, Afghan-Tajik Basin, and Marakaibo petroleum province of Venezuela). Oils initially depleted in trace elements and usually generated by humic OM also show increase in trace elements, but their concentrations are 1–3 orders of magnitude lower than those in enriched oils (oil fields in the coastal basins of Nigeria and Brazil). It was shown that supergene transformed fluids are well deciphered on the basis of a complex use of hydrocarbon and trace element criteria.     

Geochemistry and episodic accumulation of natural gases from the Ledong gas field in the Yinggehai Basin, offshore South China Sea

The Ledong gas field, consisting of three gas pools in a shale diapir structure zone, is the largest gas discovery in the Yinggehai Basin. The gases produced from the Pliocene and Quaternary marine sandstone reservoirs show a considerable variation in chemical composition, with 5.4–88% CH₄, 0–93% CO₂, and 1–23.7% N₂. The CO₂-enriched gases often display heavier methane δ¹³C values than those with low CO₂ contents. The δ¹⁵N values of the gases range from −8 to −2‰, and the N₂ content correlates negatively with the CO₂ content. The high geothermal gradient associated with a relatively great burial depth in this area has led to the generation of hydrocarbon and nitrogen gases from the Lower–Middle Miocene source rocks and the formation of abundant CO₂ from the Tertiary calcareous-shales and pre-Tertiary carbonates. The compositional heterogeneities and stable carbon isotope data of the produced gases indicate that the formation of the LD221 gas field is attributed to three phases of gas migration: initially biogenic gas, followed by thermogenic hydrocarbon gas, and then CO₂-rich gas. The filling processes occurred within a short period approximately from 1.2 to 0.1 Ma based on the results of the kinetics modeling. Geophysical and geochemical data show that the diapiric faults that cut through Miocene sediments act as the main pathways for upward gas migration from the deep overpressured system into the shallow normal pressure reservoirs, and that the deep overpressure is the main driving force for vertical and lateral migration of the gases. This gas migration pattern implies that the transitional pressure zone around the shale diapir structures was on the pathway of upward migrating gases, and is also a favorable place for gas accumulation. The proposed multiple sources and multiple phases of gas migration and accumulation model for the Ledong gas field potentially provide useful information for the future exploration efforts in this area.     

The occurrence of norlupanes and bisnorlupanes in oils of Tertiary deltaic basins

Lupanoid hydrocarbons are known to occur in several petroleum systems, and lupane (C₃₀) has recently been confirmed to exist in several crude oils. In contrast, norlupanes (C₂₉) and bisnorlupanes (C₂₈) are rarely observed in oil. All of these compounds are considered to derive from natural products of angiosperms, and numerous examples of their functionalized analogs are known. The occurrence of C₂₈ and C₂₉ lupanoids in biochemical and geochemical systems is reviewed here, and the presence and origin of their hydrocarbon analogs in crude oils are examined in detail. Although direct biochemical precursors for the lupane of crude oil are evident, such precursors for norlupane and bisnorlupane are not obvious. Nor is it clear if the C₂₈ and C₂₉ analogs are diagenetic descendants from the lupane structure. Adding additional confusion is the occurrence of these analogs in oils which show numerous indications of post-source molecular addition during migration and entrapment, making it unclear if they originate from a conventional source rock or from carrier or seal rock. Despite these uncertainties, there is extensive potential – some of which has already been realized – to use these compounds in oil–oil and oil-source rock correlations, particularly in instances where extensive biodegradation has occurred. Deconvolution of the time(s) of introduction of norlupane and bisnorlupane into the fluid – as well as various other hydrocarbons, including olefins – also provides great potential as a tool for mapping the migration history of an oil.     

The bituminous mixtures of Tall-e Abu Chizan: A Vth millennium BC settlement in southwestern Iran

Various bituminous artifacts were excavated from the Tall-e Abu Chizan, a late prehistoric (Middle Susiana to Middle Uruk) settlement on the middle of the Curvy plain, between the Karun River and the Ram Hormoz Plain. All samples dated from the Vth millennium BC and cover three periods: 5000–4700 BC (Late Middle Susiana), 4700–4200 BC (Late Susiana 1) and 4200–3900 BC (Late Susiana 2). The bitumens were studied using the techniques of petroleum geochemistry and were compared both to the unaltered crude oils produced from the main oil fields in the area and to the famous Mamatain oil seeps. All samples are very rich in bitumen (average 46 wt%) which has been biodegraded and oxidized. Despite these alteration phenomena, δ¹³C of asphaltenes occur within a narrow range of less than 1‰ PDB. Biodegradation affected the steranes, terpanes, dibenzothiophenes and mono- and triaromatic steroids. Molecular characteristics of terpanes, especially the occurrence of 18α (H)-oleanane, suggest that the bitumen from Tall-e Abu Chizan is a mixture generated from Cretaceous Kazdhumi and Eocene Pabdeh petroleum source rocks. In that respect, bitumens from Tall-e Abu Chizan belong to the same oil family as oil from the Naft Safid field, which is in the vicinity of the archaeological site. In fact, the bitumen at Tall-e Abu Chizan likely originated from oil seepages at Naft Safid. These oil seeps have not yet been sampled or analysed.     

Origin of sulfur rich oils and H2S in Tertiary lacustrine sections of the Jinxian Sag,Bohai Bay Basin,China

Very high S oils (up to 14.7%) with H₂S contents of up to 92% in the associated gas have been found in the Tertiary in the Jinxian Sag, Bohai Bay Basin, PR China. Several oil samples were analyzed for C and S stable isotopes and biomarkers to try to understand the origin of these unusual oil samples.The high S oils occur in relatively shallow reservoirs in the northern part of the Jinxian Sag in anhydrite-rich reservoirs, and are characteristic of oils derived from S-rich source rocks deposited in an enclosed and productive stratified hypersaline water body. In contrast, low S oils (as low as 0.03%) in the southern part of the Jinxian Sag occur in Tertiary lacustrine reservoirs with minimal anhydrite. These southern oils were probably derived from less S-rich source rocks deposited under a relatively open and freshwater to brackish lake environment that had larger amounts of higher plant inputs.The extremely high S oil samples (>10%) underwent biodegradation of normal alkanes resulting in a degree of concentration of S in the residual petroleum, although isoprenoid alkanes remain showing that biodegradation was not extreme. Interestingly, the high S oils occur in H₂S-rich reservoirs (H₂S up to 92% by volume) where the H₂S was derived from bacterial SO₄ reduction, most likely in the source rock prior to migration. Three oils in the Jinxian Sag have δ³⁴S values from +0.3‰ to +16.2‰ and the oil with the highest S content shows the lightest δ³⁴S value. This δ³⁴S value for that oil is close to the δ³⁴S value for H₂S (∼0‰). It is possible that H₂S was incorporated into functionalized compounds within the residual petroleum during biodegradation at depth in the reservoir thus accounting for the very high concentrations of S in petroleum.     

Hydrocarbons and water in the Western Canada Sedimentary Basin — A tale of two fluids

Detailed petroleum system analysis allows the direction and extent of hydrocarbon flow to be assessed. In most parts of the Western Canada Sedimentary Basin, the major pulse of hydrocarbon generation and migration occurred as a result of the Laramide Orogeny in Late Cretaceous–Early Tertiary time. The distribution and chemistry of oils provide a detailed picture of fluid flow at this time with oil migration up to hundreds of kilometres observed. Hydrocarbon generation and migration mostly ceased once uplift of the basin commenced during Eocene time. As the basin evolved so did the hydrodynamic regime reflecting changes in topography, glaciation and other factors. This indicates possible problems with using present day hydrogeology to determine oil migration pathways although hydrogeology can help explain petroleum alteration.     

Delineating compositional variabilities among crude oils from Central Montana, USA, using light hydrocarbon and biomarker characteristics

Three compositionally distinctive groups of oils identified in central Montana by biomarker analyses are also recognized by the unique compositions of their light hydrocarbon (gasoline range) fraction. The majority of oils produced from Paleozoic pools (Pennsylvanian Tyler–Amsden interval) group into one broad category based on the distribution of C₂₀–C₄₀ biomarkers. These oils not only have the lowest Paraffin Indices and relative concentrations of normal heptane, but are readily distinguishable from the other compositional groups by using selected “Mango” parameters. However, the biomarker-based subdivision of this group into at least two sub-families is not reflected in the gasoline range fraction, suggesting little effect of source rock host lithology on the distribution of C₅–C₈ hydrocarbons. Oils occurring predominantly in Jurassic–Cretaceous reservoirs display different biomarker and gasoline range characteristics, including Paraffin Indices, K1 parameter and relative concentrations of C₇ compounds, and are classified in two separate compositional categories. In contrast to oils from the Tyler–Amsden interval, the oils produced from the Mesozoic strata are amongst the most mature oils in the study area. The unique biomarker/light hydrocarbon signatures are likely due to different source organic matter. Secondary alteration of oil due to biodegradation and migration, although recognized, appears less significant. The results indicate the overall usefulness of gasoline range compositions in delineating compositional affinities of crude oils in central Montana, clearly suggesting that the oils found in Paleozoic and Mesozoic reservoirs belong to different petroleum systems.     

Geosteranes: Identification and synthesis of a novel series of 3-substituted steranes

A novel series of 3-alkyl and 3-carboxyalkyl-5β(H)-steranes 7–10 along with a full homologous series of carboxyalkyl-sterane (C₁ to C₆) 4–6 with 3α(H)5α(H) configuration have been identified in marine-evaporitic oils from Fazenda Belém, Potiguar Basin (Brazil) on the basis of mass spectral interpretation. The synthesis of enantiomerically pure 3α-alkyl-5β(H)-cholestane and 3β-alkyl-5α(H)-cholestane standards and their coinjection with petroleum fractions confirmed the structural assignments.     

酒西盆地石油非均质性的控制因素

运用先进的分析测试手段对来自酒西盆地六个油田的 2 0多个油样进行了全油碳同位素、饱和烃气相色谱与质量色谱及正构烷烃分子碳同位素等较为全面的分析与研究。确定源岩相、水洗、生物降解作用与成熟度不是酒西盆地石油非均质性的控制因素。最后选取 1 5个油样进行中性吡咯氮化合物分析,用中性吡咯氮中的咔唑类化合物作为运移参数,较为详细地研究原油的运移分馏作用。此类化合物作为运移参数的基本原理是石油运移过程中,不同结构的咔唑类化合物与水及岩石中矿物发生吸咐作用的强烈程度不同,导致不同的运移分馏作用。根据咔唑类化合物的变化得出控制酒西盆地石油组成非均质性的主要因素是油气运移分馏作用,证实酒西盆地石油运移方向主要是从西至东,青西凹陷是其油源区。     

C24–C27 Degraded triterpanes in Nigerian petroleum: novel molecular markers of source/input or organic maturation?

The analyses, by gas chromatography and gas chromatography/mass spectrometry, of the triterpane concentrate of crude oils sampled from various oil fields of the Tertiary Niger delta have revealed the ubiquitous presence of a series of C₂₄–C₂₇ tetracyclic alkanes likely to be novel degraded triterpanes. The presence in the crude oils of a C₂₅ tricyclic alkane, apparently structurally related to the tetracyclanes, seemed consistent with the hypothesis of sequential cleavages of the terminal rings of precursor pentacyclic triterpenoid derivatives with increasing thermal transformation of the respective petroleums.The degraded triterpanes might be useful for assessing the stages of thermal evolution of petroleum in the reservoir. A possible application, to oil exploration, of the expected variations in the concentration of the polycyclanes in crude oils with different thermal histories would be in distinguishing primary (immature) oils from mature but biodegraded oils.     

Asphalts, heavy oils, ozocerite and gases in the Dead Sea Basin

Solid, liquid and gaseous hydrocarbons occur throughout the Dead Sea Basin (Israel and Jordan) both in surface exposures and in drillings. The unaltered asphalts and heavy oils are characterized by very high sulfur content (ca. 11%) with δ³⁴S = +5% and δ¹³C = −28% to −29%, low content of n-paraffins, pristane to phytane ratio of 0.5 and by containing almost exclusively VO-porphyrins. The distribution of n-paraffins in samples from deep sources shows a smooth enveloped miximizing at C_15–20. Surface and shallow samples show clear evidence of biodegradation. The ozokerite, known only from the east side of the basin, is composed primarily of long chain n-paraffins with a maximum at C₃₉. The gases known from the southern margin of the basin are composed mostly of methane.The source for the bitumens is unknown. Two hypotheses are discussed. The first is that the asphalts and heavy oils represent an alteration products of crude oil which migrated into the basin or which might have been generated in the basin itself. The second hypothesis favors an origin from low temperature alteration of organic matter from a thermally immature source.     

Fractionated aromatic petroleums and the generation of gas-condensates

Based on experimental and observational evidence, a mode of origin involving evaporative fractionation is proposed for a class of petroleums enriched in light aromatic and naphthenic hydrocarbons (benzene, toluene, meta-xylene, para-xylene, methylcyclopentane, cyclohexane, and methylcyclohexane). Progressive gas loss from gas-saturated oil is suggested as the causal mechanism, with simultaneous loss of light ends in gaseous solution, and accompanying fractionation. These processes were simulated experimentally.Residual oils exhibit the following changes in their remaining light hydrocarbons, <C₉: (1) increase in aromaticity (in aromatic hydrocarbons relative to normal alkanes of molecular weight); (2) increase in “normality” (in unbranched alkanes and naphthenes relative to branched isomers), and (3) decrease in paraffinicity (in paraffins relative to naphthenes). Retrogressive changes in maturity indicators take place leading to spurious evidence of immaturity in residual oils and the derived evaporative condensates.The phenomena occur in many basins, and are a key to understanding major aspects of petroleum variability. On the basis of aromaticity and paraffinicity relationships, evaporative gas-condensates are distinguishable from those generated by thermal cracking. Unfractionated thermal gas-condensates are rare. Evaporative condensates are the daughter products of oils which have suffered evaporative fractionation.     

Carbon isotopic composition of individual n-alkanes in asphaltene pyrolysates of biodegraded crude oils from the Liaohe Basin, China

Biodegraded oils are widely distributed in the Liaohe basin, China. In order to develop effective oil-source correlation tools specifically for the biodegraded oils, carbon isotopic compositions of individual n-alkanes from crude oils and their asphaltene pyrolysates have been determined using the gas chromatography–isotope ratio mass spectrometry technique. No significant fractionation in the stable carbon isotopic ratios of n-alkanes in the pyrolysates of oil asphaltenes was found for anhydrous pyrolysis carried out at temperatures below 340°C. This suggests that the stable carbon isotopic distribution of n-alkanes (particularly in the C₁₆–C₂₉ range) in the asphaltene pyrolysates can be used as a correlation tool for severely biodegraded oils from the Liaohe Basin. Comparison of the n-alkane isotopic compositions of the oils with those of asphaltene pyrolysates shows that this is a viable method for the differentiation of organic facies variation and post-generation alterations.     

Metal enrichments in solid bitumens: A review

The association of oils and solid bitumens with ore deposits is widely recorded. The oils and bitumens may actually be enriched with metals. Unlike oils, metal enrichments within bitumens do not reflect the role of petroleum as a transporting agent for metals. By contrast, they may be a result of the reduction of metal ions on contact with bitumen, and may reach levels so high that ore mineral inclusions are precipitated. Metal determinations of British bitumens suggest that new metal anomalies can be detected by this approach, that some metal anomalies within bitumens may be related to ore mineralization, and that bitumens from different sources may be distinguished by their metal contents. The potential use of bitumen distribution and/or metal enrichment within bitumen for ore exploration is dependent on the metal concerned, and in particular whether the metal is transported by association with organic materials or reduced in the presence of organic materials.     

Changes of acoustic emission and strain in hard coal during gas sorption–desorption cycles

The cylindrical coal samples were subjected to three successive cycles of sorption–desorption processes of a single gas (CO₂, CH₄). Acoustic emission (AE) and strains were simultaneously recorded during the sorption and desorption processes.Tests were conducted on medium-rank coal from the Upper Silesia Basin, Poland. Follow-up tests for gas sorption–desorption consistently showed significant changes of AE characteristics for re-runs on the same sample. The AE level decreased in each successive test. The most spectacular differences were observed between AE generated during the first cycle of gas sorption and the subsequent cycle. This phenomenon could be due to structural changes in the coal taking place substantially on its first exposure to the sorbate. The AE results indicate, that each cycle of gas sorption–desorption was run on the same coal though with a somewhat different structure.In those tests, the swelling of coal by CO₂ or/and CH₄ was anisotropic (greater in the direction perpendicular to the bedding plane than parallel) in each cycle of the gas sorption–desorption process.     

Source Rocks for the Giant Puguang Gas Field, Sichuan Basin: Implication for Petroleum Exploration in Marine Sequences in South China

Detailed geochemistry studies were conducted to investigate the origin of solid bitumens and hydrocarbon gases in the giant Puguang gas field. Two types of solid bitumens were recognized: low sulfur content, low reflectance (LSLR) solid bitumens in sandstone reservoirs in the Xujiahe Formation and high sulfur content, high reflectance (HSHR) solid bitumens in the carbonate reservoirs in the Lower Triassic Feixianguan and Upper Permian Changxing formations. Solid bitumens in the Upper Triassic Xujiahe Formation correlate well with extracts from the Upper Triassic to Jurassic nonmarine source rocks in isotopic composition of the saturated and aromatic fractions and biomarker distribution. Solid bitumens in the Feixianguan and Changxing formations are distinctly different from extracts from the Cambrian and Silurian rocks but display reasonable correlation with extracts from the Upper Permian source rocks both in isotopic composition of the saturated and aromatic fractions and in biomarker distribution, suggesting that the Permian especially the Upper Permian Longtan Formation was the main source of solid bitumens in the carbonate reservoirs in the Feixianguan and Changxing formations in the Puguang gas field. Chemical and isotopic composition of natural gases indicates that the majority of hydrocarbon gases originated from sapropelic organic matter and was the products of thermal cracking of accumulated oils. This study indicates that source rock dominated by sapropelic organic matter existed in the Upper Permian and had made major contribution to the giant Puguang gas field, which has important implication for petroleum exploration in marine sequences in South China.