沉积岩中总有机碳测定的自动预处理方法

总有机碳(TOC)是衡量烃源岩有机质丰度的首要指标,实现其高效准确测定具有重要的现实意义。在TOC整体测试流程中,用稀盐酸去除无机碳的样品预处理过程目前主要采用手动法进行,存在周期长、氯化物残留等问题,成为制约整体测试效率的首要因素。学者们研究了溶样时间、溶样温度、离心洗样等对TOC测定值的影响,但尚未形成系统的预处理方法,预处理效率也未得到实质性改善。本文利用自主研制的有机碳自动预处理仪建立了两种自动预处理方法;根据国家标准 《沉积岩中总有机碳的测定》(GB/T 19145—2022)规定的预处理流程,采用多种岩性、不同TOC水平的国家标准物质和质量控制样品对这两种预处理方法进行了方法验证;并进一步分析了自动预处理方法的优势。结果表明,两种自动预处理的方法回收率总体为96.23%～102.12%,相对标准偏差为0.37%～3.23%,满足标准规定的数据准确性、重复性和再现性要求,数据质量较手动法得到进一步提升;自动预处理法的预处理时长大幅缩短至4～6h/批,提高了测试效率;氯离子活度对洗样次数的变化更为敏感,且可监测并有效降低样品中氯化物的残留量,建议作为洗样终点的定量监测指标。建立的两种自动预处理方法可替代手动法进行TOC测试的样品预处理,在保障数据质量和测试效率的前提下又可解放人力,使总有机碳的测试能力得以显著提升。     

页岩组分对五峰-龙马溪组与牛蹄塘组页岩孔隙发育差异的影响——以渝东南焦页1井与湘西北慈页1井为例

根据页岩样品不同孔径范围的累计孔体积与累计比表面积,结合焦页1井五峰-龙马溪组与慈页1井牛蹄塘组页岩样品的地球化学参数与岩样各矿物组分百分含量,分析页岩组分对两套地层孔隙发育差异的影响.结果显示,TOC与微孔呈正相关关系,表明有机质微孔对页岩孔隙发育提供了一定的贡献,五峰-龙马溪组页岩较牛蹄塘组更为发育有机质微孔.石英、黄铁矿含量与微孔的正相关关系表明,矿物支撑的原生孔与发育的边缘孔为页岩孔隙发育提供了有利贡献.石英与中孔、大孔的不同相关性表明石英根据其生物成因贡献的石英含量对中孔、大孔的保护程度不一.黄铁矿含量与大孔的正相关关系表明黄铁矿可以根据其含量的多寡为大孔提供一定程度的保护,长石与孔隙的负相关关系表明其对孔隙的支撑作用受到了压实作用、复杂构造的影响而不明显.碳酸盐矿物与孔隙的相关性不明显表示基于其较弱刚性、不稳的化学性质与较低含量未对孔隙发育产生明显影响.五峰-龙马溪组页岩较高的刚性矿物含量对储层矿物粒间孔、边缘孔等微孔与中孔、大孔的发育起到了较牛蹄塘组更为有利的影响.黏土矿物与微孔、中孔的负相关关系表明在较强压实作用下黏土矿物间孔隙易收缩,对储层孔隙发育产生不利影响,表明牛蹄塘组经历的更深历史埋藏对牛蹄塘组黏土矿物间孔隙发育起到了更加不利的影响.     

黔东页岩复电阻率各向异性及其与页岩气储层参数关系研究

电法勘探因其成本低、效率高的优势,常被作为寻找页岩气储层的辅助手段.然而,到目前为止,页岩的电性特征,特别是复电阻率各向异性特征,以及其与页岩气储层参数的关系研究甚少,这在一定程度上阻碍了电法勘探在页岩气勘探中的应用.基于此,本文采集了黔东地区几种典型黑色页岩岩样,并测量了6块黑色页岩在走向、倾向和垂直层理方向的复电阻率,分析了其各向异性特性,讨论了电阻率与总有机碳(TOC)含量、脆性矿物含量、最大镜质组反射率等页岩气储层参数之间的关系.研究表明：(1)页岩复电阻率振幅各向异性存在频率依赖的特征,在中低频阶段,页岩复电阻率振幅各向异性明显,垂直层理方向复电阻率振幅显著大于走向、倾向方向复电阻率振幅,但随频率增加,页岩复电阻率振幅各向异性差异减小,甚至趋于各向同性;(2)复Cole-Cole模型能很好地拟合页岩三方向的复电阻率数据;(3)走向、倾向方向电阻率与TOC含量存在显著的线性正相关关系,通过走向、倾向方向电阻率预测TOC含量有一定可行性;(4)电阻率与脆性矿物含量、黏土矿物含量、最大镜质组反射率关系复杂,未发现简单的线性相关关系.上述研究结果对我们全面了解黔东地区黑色页岩的电性特征,促进电法勘探在页岩气勘探中的应用大有裨益.

     

Pollution and eutrophication history AD 1800–2005 as recorded in sediments from five lakes in Central Chile

One of the fundamental problems to quantifying past impact of anthropogenic activities is that long series of observational data for pollutant deposition and changes in the nutrient cycling of ecosystems (eutrophication) are often not available. Lake sediments may provide suitable archives to decipher the history of local and regional pollution and eutrophication.Here we provide quantitative high-resolution data for the history of airborne pollutants and eutrophication from sediments of five lakes in Central Chile between ca. AD 1800–2005. We use spheroidal carbonaceous particles (SCPs) from fossil fuel combustion and excess atmospheric Cu deposition from mining activities as a proxy for atmospheric deposition. Organic carbon and nitrogen flux rates to the sediments and C/N ratios are used as a proxy for aquatic primary production and eutrophication.We show that the lake sediment SCP and Cu records are highly consistent and depict in great detail the local and regional history of urban, industrial and transportation history as reported in independent documentary sources and statistics. The pre-industrial and pre-1950 background concentrations (and flux rates) of the substances can be quantified. We can also show that technical measures taken in the early 1980s to trim down Cu emissions from the copper mines reduced the excess atmospheric Cu fallout to the lakes by about 50%.Eutrophication of the lakes did not start before ca. 1980. Prior to that time, warm season temperatures explain most of the variance in TOC and N flux to the sediments. The three dimictic lakes show only moderate eutrophication responses to enhanced N supply (as atmospheric fallout; enrichment factors for TOC and N 1.1–2.6), suggesting that mainly phosphorus controls aquatic primary production. The meromictic lake, where phosphorus recycling is likely, shows the largest response (enrichment factors for TOC and N between 9–20).While all five lakes show overall consistent and similar trends for the pollution history during the 19th and 20th century, there are significant differences in the details of the individual profiles. This suggests that local sources are highly important and the common regional (background) signal is relatively marginal. This is very different from Europe.     

柴达木盆地察尔汗盐湖CH0310钻孔沉积物磁化率及其影响因素分析

通过对长为523 m的柴达木盆地察尔汗盐湖CH0310钻孔沉积物岩性、磁性特征、高频质量磁化率、低频质量磁化率、频率磁化率和总有机碳（TOC）的实验分析,结果表明:CH0310钻孔中磁铁矿是沉积物磁化率的主要贡献者;由于受气候和环境的影响与控制,以弱氧化环境为主CH0310钻孔中沉积物的磁化率与粗砂粒级含量成正相关与粘土级含量反相关关系;进一步对磁化率和TOC的相关性分析发现,在不同的沉积层磁化率和TOC的相关性表现出正负差异,这反映了磁化率对气候与环境的响应模式在CH0310钻孔不同层位并不完全相同,揭示出湖泊磁化率影响因素的复杂性和它作为气候代用指标的不确定性,因此认为对于地处高原干旱区沉积速率快、沉积层特别厚的湖泊来说,如果用单一的磁化率指标来反映或恢复古气候和古环境的变化需要特别慎重。     

Lower Cretaceous anoxic conditions IN the Austral basin,south-western Gondwana,Patagonia Argentina

The reconstruction of palaeo-oxygenation levels in marine deposits from the Cretaceous has obtained a huge interest all around the world in recent years. This fascinating topic is here pointed out for the first time in the Austral Basin using the information provided by the black shales of the Río Mayer Formation, Patagonia, Argentina. The combination of sedimentology, ichnology and geochemistry (TOC, Ce anomaly and MnO content) allow the identification of three major intervals respecting the oxygen content. During the Berriasian and early Valanginian anoxic conditions prevail in the outer shelf. After that, between the late Valanginian and Hauterivian dysoxic palaeoenvironments were developed. Finally, a more oxygenated palaeoenvironment occurred since Aptian associated with a progradation of a proximal deltaic system. The identification of anoxic conditions is of much interest for the hydrocarbon research in this stratigraphical unit, which represents the most significant source rock of the Austral Basin.     

The Cenomanian/Turonian oceanic anoxic event in the Razzak Field, north Western Desert, Egypt: Source rock potential and paleoenvironmental association

The Western Desert of Egypt is one of the world’s most prolific Jurassic and Cretaceous hydrocarbon provinces. It is one of many basins that experienced organic-rich sedimentation during the late Cenomanian/early Turonian referred to as oceanic anoxic event 2 (OAE2). The Razzak #7 oil well in the Razzak Field in the northern part of the Western Desert encountered the Upper Cretaceous Abu Roash Formation. This study analyzed 23 samples from the upper “G”, “F”, and lower “E” members of the Abu Roash Formation for palynomorphs, particulate organic matter, total organic carbon (TOC) and δ¹³C_org in order to identify the OAE2, determine hydrocarbon source rock potential, and interpret the depositional environment. The studied samples are generally poor in palynomorphs, but show a marked biofacies change between the lower “E” member and the rest of the studied samples. Palynofacies analysis (kerogen quality and quantity) indicates the presence of oil- and gas-prone materials (kerogen types I and II/III, respectively), and implies reducing marine paleoenvironmental conditions. Detailed carbon stable isotopic and organic carbon analyses indicate that fluctuations in the δ¹³C_org profile across the Abu Roash upper “G”, “F”, and lower “E” members correspond well with changes in TOC values. A positive δ¹³C_org excursion (∼2.01‰) believed to mark the short-term global OAE2 was identified within the organic-rich shaly limestone in the basal part of the Abu Roash “F” member. This excursion also coincides with the peak TOC measurement (24.61 wt.%) in the samples.     

Episodic stream water pH decline during autumn storms following a summer drought in northern Sweden

The sources of episodic pH decline in four streams from northern Sweden during the autumn of 1996 were quantified. The events, in which pH dropped by between 1·0 and 2·4 units, were preceded by an extensive summer drought. Total organic carbon, which increased 100% to 160% during peak flow, was the most important driving mechanism of the episodic pH decline. Sulphate, however, was relatively more important during these autumn events than during spring flood. In the sites where past and present anthropogenic deposition were believed to be the main source of sulphate in stream water, sulphate contributed less than 0·3 pH units to the pH decline. In catchments where natural sources of sulphate are known to be important, sulphate contributed up to 0·6 units of pH decline. The export of sulphate during the episodes was two to nine times higher than what was expected from deposition only. The drought preceding the study episodes resulted in some of the lowest ground water levels during the 1990s in that region. The large export of sulphate was probably due to oxidation of natural sulphate bearing minerals in the soil and/or previously deposited sulphate driven by the low ground water level preceding the episodes. Copyright © 2002 John Wiley & Sons, Ltd.     

Quick Evaluation of Present-Day Low-Total Organic Carbon Carbonate Source Rocks from Rock-Eval Data: Middle–Upper Ordovician in the Tabei Uplift, Tarim Basin

Previous studies have postulated the contribution of present-day low-total organic carbon(TOC) marine carbonate source rocks to oil accumulations in the Tabei Uplift, Tarim Basin, China. However, not all present-day low-TOC carbonates have generated and expelled hydrocarbons; therefore, to distinguish the source rocks that have already expelled sufficient hydrocarbons from those not expelled hydrocarbons, is crucial in source rock evaluation and resource assessment in the Tabei Uplift. Mass balance can be used to identify modern low-TOC carbonates resulting from hydrocarbon expulsion. However, the process is quite complicated, requiring many parameters and coefficients and thus also a massive data source. In this paper, we provide a quick and cost effective method for identifying carbonate source rock with present-day low TOC, using widely available Rock-Eval data. First, we identify present-day low-TOC carbonate source rocks in typical wells according to the mass balance approach. Second, we build an optimal model to evaluate source rocks from the analysis of the rocks' characteristics and their influencing factors, reported as positive or negative values of a dimensionless index of Rock-Eval data(IR). Positive IR corresponds to those samples which have expelled hydrocarbons. The optimal model optimizes complicated calculations and simulation processes; thus it could be widely applicable and competitive in the evaluation of present-day low TOC carbonates. By applying the model to the Rock-Eval dataset of the Tabei Uplift, we identify present-day low-TOC carbonate source rocks and primarily evaluate the contribution equivalent of 11.87×10~9 t oil.     

刺参养殖池塘一种塑料人工参礁表面生态学特征初步研究

人工参礁在中国刺参(Apostichopus japonicus (Selenka))养殖业中被广泛应用,本文调查了2008年春、秋季刺参池塘中一种塑料人工礁表面的生物群落结构.采用沉积物捕捉器的方法调查了刺参池塘人工礁表面碳、氮、磷的循环及参礁的生态特征.结果表明,春季礁体底栖动物生物量及生物多样性高于秋季,底栖动物均集中在礁体外表面的缝隙内,4月礁体表面颗粒物,底泥沉积物总有机碳(TOC)平均含量分别为41.9 mg/g 和2.45 mg/g;总氮(TN)平均含量分别为4.1 mg/g 和0.2 mg/g.10月礁体表面颗粒物,底泥沉积物 TOC 含量分别为27.5 mg/g 和3.1 mg/g; TN 平均含量分别3.1 mg/g 和0.3 mg/g.4月 TOC, TN 沉积量分别达到711.2 mg/(m2·d)和70.7 mg/(m2·d);10月 TOC, TN 沉积量分别为804.9 mg/(m2·d)和87.3 mg/(m2·d).4月人工礁表面叶绿素/脱镁叶绿素(Chl a/Pheophytin)>1,表明礁体活体藻类较多.10月人工礁表面 Chl a/Pheophytin<1表明礁体表面降解颗粒物质较多.人工礁为刺参提供遮蔽场所,其表面生物膜为刺参提供优质食物,同时可增加池塘底面积,增强养殖系统稳定性.