油气藏上方地层中不同赋存态微渗漏轻烃特征初步模拟实验研究

油气藏的微渗漏烃类在岩石和土壤中的赋存状态,现阶段都已经建立起相应的分析方法,包括酸解烃、热释烃、顶空气轻烃、游离烃等,但各方法分析的静态数据尚不能准确描述微渗漏烃类在上覆地层和土壤介质中的赋存状态及特征。以往对于微渗漏轻烃赋存机理大多数研究限于理论层面,一直缺乏可靠的模拟实验结果支持,导致化探工作者对上述各类轻烃指标在应用上存在不同认识,以及对指标具有独立性存在质疑,从而影响了方法的合理应用和化探异常的解释。针对上述问题,以烃类微渗漏的简化理论模型为基础,开展烃类通过盖层及上覆地层垂向微渗漏模拟实验,对实验后的模拟柱体进行解剖,根据不同类别样品（气、岩）的分析测试结果,对游离烃、顶空气轻烃、热释烃、酸解烃在地层中的赋存机理进行了初步研究。结果表明,游离烃指标最能反映烃类垂向微渗漏的现今面貌,酸解烃指标短期内不受气体运移的影响,热释烃指标短期内受到气体运移的影响,顶空气轻烃指标受气体运移影响最显著。不同相态的烃类在岩石和土壤中赋存机理不同,受到影响因素不同,能从不同侧面反映油气微渗漏特征。上述实验结果有助于加深对油气化探不同类型轻烃指标的认识,更好地解释地球化学异常的地质意义。      

一种物理吸附烃解吸密封罐及其化探应用效果

油气藏中的轻烃可以以微弱但可检出的量近似垂直地渗漏到地表土壤中,其中一部分烃类以物理吸附态赋存在土壤或岩石颗粒表面。物理吸附烃是反映现今油气藏是否存在的最直接指标之一,因此在油气地球化学勘探中得到了广泛的重视和应用。以往对于提取土壤物理吸附烃的方法主要有密封盐水瓶顶空间轻烃技术和物理吸附气技术,在方法手段上存在一定的缺陷。针对以往技术存在的问题,自行设计、研制一种新型土壤物理吸附烃真空解吸密封罐,集样品全密封、移动活塞负压脱气、正压抽气,能够充分提取土壤、岩石、水介质样品中物理吸附烃组分和含量,装置小巧,操作简单,方便实用,适合批量样品的气体解吸实验。经过对济阳坳陷惠民凹陷南坡临南油田上方野外现场采集的新鲜土壤样品进行处理,获得的烃类组分含量远远高于传统顶空气技术所提取的烃类含量的3～4倍,且C₁-C₅组分齐全,所反映的油气微渗漏异常区与背景区分离明显,先验效果显著,为预测地下油气藏提供了有效的技术指标,具有良好的推广应用前景。     

EVALUATION OF HYDROCARBON PROSPECTS USING SURFACE GEOCHEMICAL DATA WITH CONSTRAINTS FROM GEOLOGICAL AND GEOPHYSICAL OBSERVATIONS: SAURASHTRA BASIN,INDIA

The Saurashtra Basin in western India is considered to have significant hydrocarbon potential. However conventional exploration methods, particularly for Mesozoic prospects, have been hampered by the thick basalt cover. In this study, near‐surface geochemical methods are used to investigate the generation of thermogenic gaseous hydrocarbons in the basin. Shallow soil samples were collected from favourable locations identified by integrated geophysical and geochemical studies. The compositional and isotopic signatures of adsorbed gaseous hydrocarbons (methane through pentane) together with soil iodine concentrations were used as surface indicators of petroleum micro‐seepages. High concentrations of adsorbed thermogenic methane (C₁= 518 ppb) and ethane plus higher hydrocarbons (ΣC₂₊= 977 ppb) along with iodine concentrations up to 68.5 ppm were observed. Total organic and inorganic carbon (TOC and TIC) measurements, fluorescence and X‐ray diffraction (XRD) studies showed that the near‐surface hydrocarbon occurrences were seepage related. Elevated hydrocarbon and iodine concentrations were coincident with dykes and lineaments in the study area, which probably served as conduits for the micro‐seepage of hydrocarbons.     

LIGHT HYDROCARBONS IN SOIL GAS ABOVE PROSPECTIVE OIL‐ AND GAS‐BEARING STRUCTURES: POMERANIAN SYNCLINORIUM,NW POLAND

The occurrence of methane and heavier homologues and unsaturated hydrocarbons was recorded in 226 soil gas samples recovered from a study area in the Pomeranian Synclinorium, NW Poland. Samples were collected at stations located along three survey lines (I–I', II–II’ and III–III') at a 200 m spacing. Concentrations of methane, total alkanes (C₂‐C₄) and total alkenes (C₂‐C₄) reached 13.7 vol. %, 18.4 ppm and 0.56 ppm, respectively. Soil gas alkanes heavier than methane were interpreted to be derived from subsurface hydrocarbon accumulations. These hydrocarbons migrated up into the near‐surface zone along structural discontinuities and fractures which were observed on seismic profiles. The migration rate of hydrocarbons from subsurface accumulations towards the surface was determined by the ethane/ethylene (C₂/C₂₌) ratio. The statistical distribution of the ethane:propane (C₂/C₃) ratio and plots of the C₂/C₃+C₄ and C₁/C₂+C₃ ratios indicated that accumulations of condensate, gas or oil with a gas cap probably occur in the study area. Variations in normalized values of total alkane C₂‐C₄ concentrations allowed surface geochemical anomaly zones to be identified. These anomaly zones were evidence for the occurrence of subsurface hydrocarbon accumulations. Hydrocarbon accumulations are most likely to occur beneath the central part of profile II–II' and may also occur in the SW and NE parts of profile III–III' where both the Carboniferous and the Zechstein Main Dolomite are prospective. In these areas, hydrocarbon accumulations may occur in fault‐bounded anticlinal highs. Surface geochemical anomalies also confirm the presence of a non‐commercial hydrocarbon accumulation in the Main Dolomite which was discovered by the D‐1 well, and the possibility of another subsurface accumulation in an adjacent tectonic block. Soil gas analyses combined with seismic data provide evidence for the hydrocarbon prospectivity of the study area.     

微量元素方法在地表油气化探中的试验研究——以川西新场气田为例

在证实四川盆地西部新场气田上方存在烃类微渗漏现象的基础上,于该区开展微量元素与有机地球化学测量,研究了土壤中微量元素指标与有机地球化学指标的相关性及其与油气微渗漏的关系。新老资料的对比研究反映了微量元素指标的稳定性和对油气的指示意义。根据多元统计,结合已知气田上方微量元素反映油气异常的效果,认为Cl、S、V、Ni、Cu、Zn、Sb、Cr、Co、Ba、Mo、Mn、Fe、Fe/Mn、V/Ni等微量元素指标与气田区存在着响应关系,为该区预测天然气的有效指标。同时对新场气田上方微量元素指标异常特征的地质意义进行了探讨。优选已知气田上方的微量元素有效指标组合对于今后在该区进行大面积的油气远景评价,具有指导和现实意义。      

油气微渗漏组分的赋存形态及其油气指示性

按赋存介质类型和与介质作用方式，油气微渗漏组分可以划分为挥发态、水溶态、吸附态、吸收态、包裹态和化合态。目前已根据不同赋存形态确立了十多种油气地球化学勘探方法。提出评价地球化学勘探方法检测油气有效性的油气指示性指标（SI）。用该指标评价鄂尔多斯盆地不同地区中所应用的5种地球化学方法，依SI值由大到小的排序为微量元素电化学提取，酸解烃，热释汞，金属总量分析和蚀变碳酸盐(二者SI值相同)。有效性评价结果表明，微量元素吸收态的电化学提取方法具有很好的油气指示性和对油气藏边界的分辨能力，微量元素的谱图分析可作为油气微渗漏异常属性评价的一种新手段。图2表1参10（文百红摘）     

松辽盆地南部十屋断陷地表烃类异常特征及油气指示意义

地表油气化探技术根据油气微渗漏在地表的异常显示特征预测深部油气藏,已经有70余年历史。大多数人都认可油气藏能发生油气微渗漏这一自然现象,但对深部油气藏与地表化探异常之间的复杂关系尚存疑虑。十屋断陷已知油气藏油气微渗漏检测结果显示,该区各项化探指标均为低背景非均匀地球化学场特征,异常点浓度较高;与油气藏有关的异常呈环状或复杂环状形态,受断层和盖层条件影响而产生的异常为条带状或块状形态。油藏和油气藏微渗漏异常特征不同,气田上方异常强度低,为简单环状;而油气田上为复杂环状(环内也有部分指标异常)。     

Biodegradation of petroleum hydrocarbons by soil microflora activated with photoluminescent films

Films on the oxygenase activity of indigenous microflora in oil-polluted soils having an oil concentration of 50 g/kg was studied. The oil utilization in experiments was 30–35 g/kg of soil versus 8–13 g/kg in the control. The IR spectroscopic determination of residual petroleum hydrocarbons showed the appearance of absorption bands at 1710 and 1600 cm^?1, as well as an increase in the spectral coefficients C₁, C₂, A₁, A₂, and A₂ by a factor 1.5–3 and a decrease in C₃ and A₃ by a factor 1.5–2.5, thus indicating intense oil oxidation in the presence of photoluminescent films. Chromatographic analysis data corroborated the occurrence of intense bio-degradation of acyclic saturated hydrocarbons. In experimental samples, light C₉–C₁₄ hydrocarbons completely disappeared and the concentration of higher C₁₅–C₂₈ hydrocarbons decreased by 70–80%. The oil biodegradation factor defined as the ratio of total isoalkanes (pristane + phytane) to total n-alkanes (C₁₇ + C₁₈) increases 5–6-fold when the photoluminescent films are used.     

Influence of soil moisture on the results of surface geochemical survey applied to petroleum exploration

The quality of results obtained from surface geochemical exploration depends not only on the character of deep petroleum accumulations but also on the influence of many sub-surface factors. One of important factors is the presence of soil moisture in the sampling interval. This research presents the influence of soil moisture on concentrations of gaseous hydrocarbons in sampled soil gases. The comparative analysis was made on for two populations of gaseous hydrocarbon (methane, ethane, propane, i-butane, n-butane, propylene, 1-butene) concentrations measured in soil gas samples collected from the water-saturated (“wet” sampling interval) and water-free (“dry” sampling interval) environments. The comparison was based upon chromatographic analyses of 2974 samples of soil gas, in which 684 samples originated from “wet” sampling intervals and 2290 samples were taken from “dry” interval. Samples were collected in the areas of known gas deposits located in the Fore-sudetic Monocline (SW Poland). Samples collected from the “wet” intervals reveal higher concentrations of almost all analyzed hydrocarbons in comparison with samples from “dry” intervals. Highest differences were observed for methane concentrations and lowest — for total alkanes C₂–C₄. The increase of concentrations in “wet” sampling intervals can be explained by sub-surface accumulation of hydrocarbons caused by decreasing permeability of water-saturated soils, by the different solubilities of alkanes and alkenes in water as well as by recent generation of methane and alkenes. Considering the results obtained from the area of the Tarchaly gas deposit, it was found that surface pattern of methane anomalies does not reflect the presence of deep gas accumulations, as well as the total alkanes C₂–C₄ distribution. Hence, the procedure was proposed of elimination of soil moisture influence on the pattern of surface methane anomalies. The procedure includes normalization of measured methane concentrations to the reference levels of geochemical background, which characterize “wet” and “dry” sampling intervals. As a result, the distribution of anomalous methane concentrations was obtained, which, along with the distribution of total alkanes C₂–C₄, confirms the presence of assessed accumulation of gaseous hydrocarbons. Therefore, the proposed method is correct and supports the application of methane indicator as a petroleum exploration tool.     

烃类垂向微渗漏近地表显示与运移通道的关系——以苏北盆地盐城凹陷朱家墩气田为例

烃类垂向微渗漏是油气化探的理论基础,在地表形成的化探异常形态和特征受油气分布、盖层、断裂与裂隙系统、储层流体属性等因素影响。为了研究油气藏中烃类垂向微渗漏近地表异常显示的主要受控因素,在苏北盆地盐城凹陷朱家墩气田上方近地表开展了以游离烃、顶空气法为主的地球化学勘探研究。结果显示,这些活跃的烃类指标异常分布与下伏气藏上方的优势运移通道具有良好的响应关系,表明油气藏中的烃类垂向微渗漏至地表是客观存在的事实。通过对已知气藏封盖条件和运移通道的分析,认为对该气田上方烃类垂向微渗漏的近地表异常显示起主控作用的是断层、盖层中的裂缝发育带和地层中的微裂缝系统。试验结果为今后研究油气藏上置化探异常模式及成因机理提供了较好的证据。      

Light hydrocarbon geochemistry of crude oils from Eastern Niger Delta

Abstract

Geochemical evaluation of oil samples from the eastern part of the Niger Delta divided into western, eastern, and central sections of the study area was carried out for the characterization of their light hydrocarbons content in order to correlate oils from different parts. The hydrocarbons in the oil samples were determined using gas chromatographic (GC) technique. The results obtained showed that CPI, Pr/Ph, Pr/nC₁₇, and Ph/nC₁₈ ratios ranged from 0.99–1.55, 2.19–4.79, 0.92–2.35, and 0.27–0.47, respectively. The Pr/nC₁₇ versus Ph/nC₁₈ plot showed that the oils were derived from terrestrial organic materials that were deposited under oxic to suboxic conditions. They are moderately matured with minimal effect of biodegradation on most of the oil samples although two of the oils showed relatively higher degradation. Both bivariate and multivariate plots of the light hydrocarbon ratios differentiated the western and central oils from the eastern oils. The classification of the oils into families was not based on origin but rather on post generative alterations that include reservoir conditions and possibly migration effects. The light hydrocarbon parameters identified can be used in the correlation tools.     

内蒙古沙漠覆盖区油气化探应用实例

沙漠覆盖区是油气勘探难度较大的地区之一。为探索在沙漠区可行的地球化学勘探方法，进行了一系列地球化学方法实验，除了常规的地球化学检测方法外，还开展了游离烃方法的实验研究，以检验在沙漠区能否采集到合格的游离烃样品，以及该方法能否对地下油气源有指示作用。实例证明：在沙漠覆盖区，油气地球化学勘探是一种有效的方法；游离烃和顶空气能很好地检测到油气微渗漏信息，对下伏油气藏有着很好的指示作用，是进行油气勘探的主要地球化学方法；其他烃类指标及荧光光谱和ΔC则可以作为辅助指标，增加油气信息检测的可信度。     

Oil-source correlation and the impact of oil-filling process on geochemical composition of the different states of oils in the Upper Triassic Chang 7 Formation,Ordos basin,China

Five crude oil samples from five wells and 33 oil-containing sandstone reservoir rock samples from six wells of Chang 7 sub-unit were systematically studied to determine hydrocarbons in these oil reservoirs whether are the mixtures of oil components derived from different source rocks or from the same source rock during oil filling process over geological times. Sequential extraction was applied to the oil-containing reservoir rocks to deserve the free and adsorbed oils. The distribution of alkanes, hopanes and steranes and the correlation diagram of Pr/n-C₁₇ versus Ph/n-C₁₈ show that these oil components and crude oils have similar parent materials. And on this basis we compared the thermal maturity of the crude oils, the free oils and adsorbed oils and found that the thermal maturity of these oils is different. The cross plot of C₂₉αα-20S/(20S+20R) versus C₂₉ββ/(αα+ ββ) and the correlation diagram of Pr/n-C₁₇ versus Ph/n-C₁₈ both show that the crude oils have highest thermal maturity, followed by the free oils and then the adsorbed oils. The ratios of ∑C₂₁^?/∑C₂₂⁺ for the crude oils and free oils are greater than the adsorbed oils, indicating the crude oils and free oils have suffered more thermal stress and extensive cracking than that of the adsorbed oils. These geochemical data reveal that hydrocarbons in these oil reservoirs and crude oils were derived from the same source rock with different thermal maturity over geological times.     

Methane in soil gas and its transfer to the atmosphere in the Yakela condensed gas field in the Tarim Basin, Northwest China

In this study, by analyzing CH₄ concentration and δ¹³C_CH4 in soil-gas profiles, the potentials of CH₄ gas transfer from ground to atmosphere were studied at four representative sectors in the Yakela condensed gas field in the Tarim Basin, Xinjiang, China. These are: 1) the oil–gas interface sector, 2) fault sector, 3) oil–water interface sector, 4) an external area. Variation in CH₄ in soil-gas profiles showed that CH₄ microseepage resulted from the migration of subsurface hydrocarbon from deep-buried reservoirs to the earth’s surface. It was found that CH₄ from deep-buried reservoirs could migrate upwards to the surface through faults, fissures and permeable rocks, during which some CH₄ was oxidized and the unoxidized methane remained in the soil or was emitted into the atmosphere. The lowest level of CH₄ at the soil-gas profile was found at the CH₄ gas-phase equilibrium point at which the CH₄ migration upwards from deep-buried reservoirs and the CH₄ diffusion downwards from the atmosphere met. The δ¹³C_CH4 and ethane, propane in soil gas exhibited thermogenic characteristics, suggesting the occurrence of CH₄ microseepage from deep-buried reservoirs. A linear correlation analysis between CH₄ concentrations in soil gas and temperature, moisture, pH, Eh, Ec and particle size of soil indicated that both soil Eh and soil temperature could affect CH₄ concentration in soil gas while soil pH could indirectly influence soil methanotrophic oxidation via impacting soil Eh.     

西南油气田含锂气田水资源调查分析

截至2020年底,国内锂资源供应对外依存度高达70%。据统计,中国石油西南油气田公司(以下简称西南油气田)各气田在开发过程中普遍产水,目前西南油气田拥有生产井1 900余口,其中超80%的生产井产水,2020年常规气气田累计产水超120×10⁸ m³。据研究报道,气田水与油气等烃类物质共同经历了漫长的油气成藏阶段,通常含有更多的微量元素,甚至部分锂资源含量高于盐湖卤水。通过气田水取样分析证实,西南油气田17口井气田水中锂离子质量浓度最高达131.6 mg/L,约50%取样井气田水中锂离子含量高于最低工业品位,同时还含有较为丰富的溴、钾等伴生资源。通过对重点井气田水跟踪评价证实西南油气田气田水锂、溴资源长周期稳定性较好,此外,西南油气田地层水资源丰富,3处重点区块地层水储量达13.3×10⁸ m³,初步估算了3处区块锂资源(以Li₂CO₃计)总价值超3 100亿元,具有较大的开发利用价值。     

THE MIDDLE CAMBRIAN SUCCESSION IN THE CENTRAL BALTIC BASIN: GEOCHEMISTRY OF OILS AND SANDSTONE RESERVOIR CHARACTERISTICS

Some 36 oilfields, all producing from Middle Cambrian (Deimena Group) sandstones, are located in the central Baltic Basin in an area covering onshore Lithuania and Kaliningrad (Russia) and the adjacent offshore. This paper presents new data on the composition of crude oils from fields in this area and reviews the reservoir properties of the Deimena Group sandstones. Twenty‐one crude oil samples from fields in Lithuania and Kaliningrad were analysed by standard techniques including GC and GC‐MS. The oils had densities of 790.5 to 870.0 kg/m³, and had low asphaltene (<2.2%) and sulphur (<0.44%) contents. The gasoline fraction (b.p. >200°C) ranged from 12–34%. The saturated hydrocarbon content was 35.3 to 77.8%, and the ratio of saturate to aromatic hydrocarbons was 2.1–5.2, indicating long‐distance migration or high thermal maturities. GC analyses of saturate fractions indicated a composition dominated by n‐alkanes with a maximum at C₁₃–C₁₅ and reduced abundance in the C₂₀–C₃₅ range. The analysed crude oil samples are characterized by relatively low concentrations of steranes and triterpanes. Biomarker data indicated an algal origin for the precursor organic matter and a clastic‐dominated source rock. Sterane isomerization ratios imply that the oils are in general relatively mature. Exceptions are samples from the Juzno Olempijskoye and Deiminskoye fields, Kaliningrad, which were early mature. Oil from well Gondinga‐l (Lithuania) was lightly fractionally evaporated and has a relatively higher density, higher viscosity, higher asphaltene content and lower content of saturated fractions. Stable carbon isotope ratios of crude oils and saturated and aromatic fractions were analysed. Whole oils showed little carbon isotope variation, but there were significant differences in δ¹³C ratios for saturated and aromatic fractions. The geochemical data show differences in oil sourcing and indicate the possible existence of different kitchen areas in the Kaliningrad region. Vertical and lateral variations in Deimena Group reservoir properties are controlled by variations in quartz cementation. In fields in western Lithuania, sandstone porosity ranges from 0.7 to 20% and permeability from 20 mD to 300 mD; in fields onshore Kaliningrad, porosity is up to 34% and gas permeability up to 4.8 D. Wide variations in porosity and permeability occur at a field scale.     

Bacteria as indicators for finding oil and gas reservoirs: A case study of the Bikaner-Nagaur Basin, Rajasthan, India

Geo-microbial prospecting for hydrocarbons is an exploration method based on the seepage of light gaseous hydrocarbons from oil/gas reservoirs to the surface and their utilization by hydrocarbon oxidizing bacteria.These bacteria utilize hydrocarbon gases as their sole source of food and are found to be enriched in the near surface soils/sediments above the oil and gas reservoirs.The detection of anomalous populations of n-pentane and n-hexane oxidizing bacteria in the surface soils can help to evaluate the prospects for hydrocarbon exploration.A geo-microbial survey has been carried out in the Bikaner Nagaur basin to investigate the prospects for hydrocarbon exploration.In the present study,bacterial counts for n-pentane utilizing bacteria range between 2.0×10 2 and 1.26×10 6 cfu/gm and n-hexane utilizing bacteria range between 2.0×10 2 and 1.21×10 6 cfu/gm.The bacterial concentration distribution maps show four distinct anomalies in the study area.The possibility of discovering oil or gas reservoirs using the microbiological method is emphasized by the fact that the hydrocarbon-oxidizing bacteria range between 10 3 and 10 6 cfu/gm in soil/sediment receiving hydrocarbon micro-seepages.In the present study area of the Bikaner Nagaur basin,n-pentane and n-hexane utilizing bacteria are found between 10 5 and 10 6 cfu/gm of soil sample,which is significant and thereby substantiates the seepage of lighter hydrocarbon accumulations from oil and gas reservoirs.Geo-microbial prospecting studies suggest that hydrocarbon micro-seepage of subsurface origin is present in the study area and indicate that the area has positive prospects for petroleum exploration.     

依据热模拟实验动态建立煤成烃模式

依据构成煤岩端元组分（壳质组、镜质组和惰质组）热模拟实验的生烃潜力和甲烷同位素组成数据,结合已建立的煤成油有效排出门限(30 mg/g_TOC),建立了煤成烃模式,该模式表明：只有富氢的显微组分才有利于煤岩生油,且壳质组含量最低为5.0%,而镜质组最高含量为95.0%;当壳质组含量高于22.9%时,煤成油不受镜质组和惰质组二端元组成的影响。同时,按照煤成烃模式计算了不同端元组分在不同热演化阶段甲烷碳同位素组成的变化,结果表明：构成煤岩的显微组分含量能够引起烷烃气碳同位素组成的变化;在同一热演化阶段,甲烷碳同位素组成最大差异可达2.3‰。认为煤成气甲烷碳同位素组成不仅受热成熟度控制,而且也受煤岩显微组分相对含量的影响。     

Oil Recovery from Petroleum Sludge by Solvent Extraction

Abstract

Technical problems associated with sludge deposition in storage units of petroleum industries are enormous. The conventional methods of management are laborious and uneconomical; the hydrocarbon contents are lost to the pits, causing environmental problems. Solvent recovery of the hydrocarbons from accumulated sludge in storage facilities of oil industries in the Niger delta area of Nigeria was carried out. A recovery of about 67.5% hydrocarbon oils was obtained, out of which 86.7% were aromatic. Gas chromatographic analysis of the extracted oil showed it contained the hydrocarbons in the range of C₉–C₂₅, which is good petrochemical industry feedstock. Hexane and xylene showed high potentials for hydrocarbon oil extraction from the sludge, reducing the quantity of solid waste to the barest minimum.