Geochemical Characteristics and Origin of Tar Mats from the Yaha Field in Tarim Basin, China

Tar mats were firstly discovered and determined accurately in terrestrial oil and gas reservoirs associated with Lower Tertiary sandstone reservoirs in the Yaha field of the Tarim Basin, China, by thin layer chromatography flame ionization detector (TLC FID) and Rock Eval analysis. The relative content of asphaltene in gross composition of tar mat extracts accounts for more than 30%, that in the corresponding oil leg less than 20%. In the geochemical description profile of oil and gas reservoirs, drastic changes in asphaltene contents between tar mats and oil legs could be discovered. This is an important marker to determine tar mats. Distribution characteristics of saturated and aromatic hydrocarbons from reservoir core extracts and crude oils in the Yaha oil and gas reservoirs in the Tarim Basin are described systematically in this paper, and the results show there are similarities among n alkane distribution characteristics, biomarker distribution characteristics and their combined characteristics of saturated hydrocarbons, and the geochemical characteristics of aromatic hydrocarbons for tar mats, oil leg, asphaltic sand and crude oil. These characteristics suggest the hydrocarbons in these samples were originated from the common source rocks. However, the geochemical characteristics of tar mats revealed that the mechanism of formation of tar mats is the precipitation of asphaltene from crude oils in petroleum reservoirs caused by increased dissolved gas in oil legs (gas injection).

Discovery of tar mats in terrestrial gas-condensate reservoirs and its geological significance

TAR mat is reservoir zone containing petroleum rich in asphaltene, and is situated in gascondensate reservoirs and light oil reservoirs. Tar mat is an organic barrier for oil and gas reservoirs. Recently, determination of tar mat has become reality as thin layer chromatography-flame ionization detection(TLC-FID) technique is applied to organic geochemical de-

油气藏中沥青垫的研究进展

沥青垫是油气藏中沥青质相当富集的含油储层带，其沥青质的相对含量为２０％～６０％，而对应的油层中其值不足２０％，沥青垫在凝析油气藏和轻质油藏中出现的频率高，常位于非渗透性隔层之上的高孔隙和较高水平渗透率的砂岩储层中。研究表明沥青垫的主要形成机理为：脱沥青作用、重力分离作用、生物降解作用和油—水相互作用。

苏丹Muglad盆地FN油田沥青垫的确认及成因分析

Fula坳陷位于苏丹Muglad盆地东北部,面积约5000km2,已发现有较大规模的油气储量。FN油田是到目前为止该坳陷发现的最大油田,储量近亿吨,主要储层是上白垩统Aradeiba组和下白垩统Bentiu组。油田地质地球化学研究表明,水洗和生物降解作用是稠油形成的主要原因。该油田普遍发育有沥青垫,开发难度较大。对该油田两口井原油和油砂详细的地球化学分析以及对沥青垫成因的探讨,为进一步的油气勘探开发提供了决策依据。

文留油田25东区块沥青垫地球化学特征及成因

利用薄层色谱和全烃色谱分析并结合测井响应特征,在文留油田25东区块鉴定出3层沥青垫,其测井响应特征与油层相似,对油藏起分隔作用,主要出现在高孔隙度、高渗透率的储集层中。沥青垫富含极性组分,其含量大于40%,远高于油层抽提物中极性组分的含量。饱和烃GC-MS分析结果显示,沥青垫、油层岩心抽提物和原油中正构烷烃及生物标志物组成特征具有相似性,说明其中的烃类来自相同的烃源岩,具有相似的热演化程度,且未受到强烈的生物降解作用。沥青垫地球化学特征和测井资料表明,油田地层水体的长期冲刷与氧化作用是沥青垫形成的主要原因,沥青垫存在于油、水交互部位。

储层热解分析在沥青垫识别中的应用

沥青垫是富含沥青质的石油带。它的存在使得孔渗性较好的储集层成为油气藏中的有机隔层,降低油藏质量与油藏规模,增大了油藏的开发难度。本文通过采用储层热解分析技术手段认清了沥青垫的组分特征,并采用重轻比与PI_3指数将沥青垫、高阻层及油层的技术界限进行划分。证明储层热解分析能够在沥青垫的识别中提供重要的技术保证。

辽河油田X区块馆陶油藏沥青垫有机地化特征研究

沥青垫是富含沥青质的石油带。它的存在使得孔渗性较好的储集层成为油气藏中的有机隔层,降低油藏质量与油藏规模,增大了油藏的开发难度。本文通过采用有机地化分析技术手段认清了沥青垫的组分特征,研究发现X区块馆陶油藏沥青垫的形成可能源自于微生物降解作用后沥青质的析出。研究人员对该区沥青垫开展技术界限划分,从而为该区的沥青垫与油层的区分提供技术保证。