准噶尔盆地西部坳陷二叠系下乌尔禾组烃源岩生烃潜力评价

Hydrocarbon-generating potential of source rocks of Permian lower Urho Formation in western depression,Junggar Basin

利用岩石热解、镜下观察、热演化史分析、生烃热模拟实验及盆地模拟等手段,从岩性、有机质特征、生物标志物特征、规模有效烃源灶的分布特征等方面对准噶尔盆地西部坳陷二叠系下乌尔禾组烃源岩的生烃潜力进行了系统研究。研究结果表明:(1)西部坳陷下乌尔禾组烃源岩主要为一套纹层不明显的泥岩沉积,岩性包括深灰色泥岩、灰色粉砂质泥岩、灰色泥质粉砂岩及灰色含炭粉砂质泥岩等,局部颜色深。(2)下乌尔禾组烃源岩整体生烃潜力一般且样品间差异性明显,有机质类型主要为Ⅲ型干酪根,岩石热解氢指数HI一般小于100 mg/g,为倾气型烃源岩;有机质成熟度分布范围大,镜质体反射率Ro为0.64%~1.56%,平均1.06%,产率指数PI为0.05~0.74,平均0.33,总体位于主生油窗,现今沙湾凹陷、盆1井西凹陷和玛湖凹陷分别处在生油高峰晚期、生凝析油/湿气和生干气阶段;有机质丰度、生烃潜力差别大,TOC值为0.29%~9.16%,平均0.85%,生烃潜量(S1+S2)为0.29~3.16 mg/g,平均0.74 mg/g,样品中差烃源岩和中等—好烃源岩各占50%。(3)下乌尔禾组烃源岩以浅湖沉积为主,处于淡水、弱氧化环境,以陆源有机质输入为主,几乎无碳酸盐输入,岩性、沉积环境均与风城组烃源岩差异大,生烃潜力更小。(4)下乌尔禾组烃源岩生烃中心为盆1井西凹陷,发育规模大,其中烃源岩厚度大于100 m的区域面积达16 000 km2,生烃强度大于500×10^(4)t/km^(2)的烃源岩分布面积达6 800 km^(2),具备形成大中型油气田的资源潜力。

The hydrocarbon-generating potential of Permian lower Urho Formation source rocks in western depression of Junggar Basin were systematically studied from lithology,organic matter characteristics,biomarker characteristics and distribution characteristics of large-scale effective hydrocarbon source stoves by means of Rock-Eval pyrolysis,microexamination,thermal evolution analysis,thermal simulation experiment of hydrocarbon generation and basin modeling.The results show that:(1)The source rocks of lower Urho Formation in western depression are mainly mudstone deposits with inconspicuous laminae,and the lithologies include dark grey mudstone,grey silty mudstone,grey argillaceous silty mudstone,and grey carbonaceous silty mudstone.(2)The source rocks of lower Urho Formation have hydrocarbon-generating potential and its differences of samples is obvious,and the organic matters are mainly composed of typeⅢkerogen with the Rock-Eval hydrogen index(HI)generally less than 100 mg/g,which indicates a set of gas-prone source rocks.The maturities of organic matters vary widely with the vitrinite reflectance(Ro)ranging from 0.64%to 1.56%(1.06%on average)and the production index(PI)ranging from 0.05 to 0.74(0.33 on average).At present,the source rocks in Shawan,Pengyijingxi and Mahu sags are in the late oil-generating-peak,condensate/wet-gas-generating stage,and dry-gas-generating stage,respectively.The abundance and hydrocarbon-generating potential vary greatly with the TOC ranging from 0.29%to 9.16%(0.85%on average)and S1+S2 ranging from 0.29 to 3.16 mg/g(0.74 mg/g on average),respectively.Poor and medium-good source rocks account for 50%of the total samples respectively.(3)The source rocks of lower Urho Formation were deposited in fresh-oxidized environment,mainly with terrigenous organic matter input and almost no carbonate input.The lithology and sedimentary environment are different from that of the source rocks of Fengcheng Formation,and the hydrocarbon generation potential is lower.(4)The hydrocarbon generation center of the source rocks of lower Urho Formation is located in western well Pen-1 sag,which has a large development scale.The area of the source rocks with a thickness greater than 100 m is 16000 km2,and the area of the source rocks with a hydrocarbon generation intensity greater than 500×10^(4) t/km^(2) is 6800 km2,showing a favorable potential to form large and medium-sized oil and gas fields.