银根-额济纳旗盆地哈日凹陷下白垩统烃源岩地球化学特征与油源对比

近年来，银额盆地哈日凹陷的油气勘探呈现良好态势，但油气分布规律尚不明确，严重制约了该区的勘探进程。通过对烃源岩、原油和油砂样品进行系统的测试分析，开展烃源岩地球化学特征和油源对比研究，以期明确原油油源特征，为油气勘探提供依据。研究结果表明：下白垩统银根组烃源岩TOC平均为4.69%，R_o平均为0.62%，Pr/Ph值平均为0.34，伽马蜡烷指数平均为0.36，烃源岩为有机质丰度极高、以Ⅰ型为主、低成熟烃源岩，具有以水生生物输入为主的生源特征和强还原、微咸-半咸水、水体分层的沉积古环境。下白垩统苏红图组烃源岩TOC平均为1.04%，R_o平均为0.75%，Pr/Ph值平均为0.99，伽马蜡烷指数平均为0.28，烃源岩为有机质丰度好、Ⅱ₁-Ⅱ₂型、低成熟-成熟烃源岩，具有水生生物和高等植物混源的生源特征和还原、微咸-半咸水的沉积古环境。下白垩统巴音戈壁组烃源岩TOC平均为0.91%，R_o平均为1.31%，Pr/Ph值平均为1.18，伽马蜡烷指数平均为0.24，烃源岩为有机质丰度中等-好、Ⅱ₂-Ⅲ型、成熟-高成熟烃源岩，具有水生生物和高等植物混源的生源特征和弱还原-弱氧化、微咸-半咸水的沉积古环境。无论是正构烷烃单体碳同位素还是生物标志化合物特征，巴音戈壁组原油与巴音戈壁组烃源岩的相似程度极高，且有别于银根组和苏红图组烃源岩，表明巴音戈壁组油藏的源岩主要为巴音戈壁组烃源岩。延哈2井原油和延哈3井原油来自于凹陷不同构造部位的巴音戈壁组烃源岩，源岩热演化程度的差异导致2个原油样品在成熟度方面有较大的差异，研究区巴音戈壁组油藏具有"近源成藏、侧向运移极为有限"的特点。

Geochemical characteristics of Lower Cretaceous source rocks and oil-source correlation in Hari sag,Yingen-Ejinaqi Basin

In recent years, favorable trends of hydrocarbon exploration are shown in Hari sag, Yingen-Ejinaqi Basin. However, the distribution of oil and gas is not clear, which seriously restricts the exploration process in this area. Based on the systematic test and analyses of source rocks, crude oil and oil sand samples, a study is performed on the geochemical characteristics of source rocks and oil-source correlation, so as to ascertain the oil-source characteristics of crude oil and provide a basis for hydrocarbon exploration. The research results show that for source rocks in Lower Cretaceous Yingen Formation (K₁y for short), TOC, R_o, Pr/Ph and gammacerane index are averaged at 4.69%, 0.62%, 0.34 and 0.36 respectively. The source rocks are characterized by extremely high organic matter abundance, Type I and low maturity, presenting the hydrocarbon origin features dominated by the input of aquatic organisms as well as the sedimentary paleo-environment featured with strong reduction, brackish water and water mass stratification. For source rocks in Lower Cretaceous Suhongtu Formation (K₁s for short), TOC, R_o, Pr/Ph and gammacerane index are averaged at 1.04%, 0.75%, 0.99 and 0.28 respectively. The source rocks are characterized by favorable organic matter abundance, Type Ⅱ₁-Ⅱ₂ and low maturity-maturity, presenting the hydrocarbon origin features dominated by the mixed source of aquatic organisms and higher plants as well as the sedimentary paleo-environment featured with reduction and brackish water. For source rocks in Lower Cretaceous Bayingebi Formation (K₁b for short), TOC, R_o, Pr/Ph and gammacerane index are averaged at 0.91%, 1.31%, 1.18 and 0.24 respectively. The source rocks are characterized by medium-good organic matter abundance, Type Ⅱ₂-Ⅲ and maturity-high maturity, presenting the hydrocarbon origin features dominated by the mixed source of aquatic organisms and higher plants as well as the sedimentary paleo-environment of weak reduction-weak oxidation and brackish water. In terms of the carbon isotope of individual n-alkanes or the biomarker compound characteristics, the crude oil in K₁b is similar to the source rocks in K₁b while different from the source rocks in K₁y and K₁s, proving that the source rocks of K₁b reservoir are mainly the hydrocarbon source rocks in K₁b. The crude oil of Well Yanha 2 and Yanha 3 is sourced from the hydrocarbon source rocks of K₁b at different tectonic positions, and the differences in thermal evolution degree of source rocks result in a big deviation in maturity between two oil samples. The reservoirs in K₁b show the characteristics of "near-source accumulation and extremely limited lateral migration" in the study area.