文留油田25东区块沥青垫地球化学特征及成因

Geochemical characteristics and origin of tar mats in Eastern Block 25 in Wenliu Oilfield,Dongpu Depression

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。

Three tar mats separating reservoirs are identified in high porosity and permeability reservoirs in the east of Block 25 of Wenliu Oilfield using thin layer chromatogram - flame ionization detector （TLC-FID） and whole hydrocarbon gaschromatography. The tar mats have similar logging characteristics of oil-bed and are rich in polar composition （over 40 % ）, which is far higher than that in oil sand. Similar clan constitutions in tar-mats, oil sand and crude oil indicate their common origins. The GC/MS analysis of saturated hydrocarbon shows that n-alkane and biomarkers are similar in constitutions, proving that they come from the same source rocks, have similar thermal evolution histories and are not biodegraded sharply. Both geochemistry and well log data indicate that long-term formation water washing and oxidation action are main causes of tar mats existing in the oil-water interface.