徐家围子断陷深层烃源岩生气评价

Gas-generation evaluation of deep hydrocarbon source rocks in Xujiaweizi fault depression

采用开放和限定两种模拟实验体系,根据生烃动力学和甲烷碳同位素动力学,计算了徐家围子断陷深层烃源岩中泥岩和煤的生气动力学参数及甲烷的碳同位素分馏参数;结合盆地的热史及埋藏史,定量评价了烃源岩生气过程及甲烷碳同位素的演化情况。沙河子组泥岩和煤的生气门限深度分别为2 100m和1 750m,对应的镜质体反射率分别为0.7%和0.6%;沙河子组泥岩和煤于登娄库组沉积时期开始生气,在泉头组到青山口组沉积时期为生气高峰期,累计生气量分别为201.37×1011m3和88.39×1011m3,平均生气强度分别为250×108m3/km2和100×108m3/km2。徐深1井营城组天然气藏中平均甲烷碳同位素值介于煤成甲烷、泥岩成甲烷的累积碳同位素值之间,与泥岩成甲烷的累积碳同位素值较为接近,反映出该气藏与沙河子组煤系地层(泥岩及煤)具有亲缘性,且泥岩的贡献大于煤,气藏属于长期聚集而成。

Based on open and restriction simulation experimental system, the gas-generation process and evolvement condition of methane carbon isotope of deep hydrocarbon source rocks in Xujiaweizi fault depression were quantitatively evaluated by using hydrocarbon-generation and methane carbon isotope kinetic methods combined with heat and burial history. The results show that the source rocks of Shahezi Formation began to generate gases at the time of Denglouku Formation. The gas-generation peak period is from Quantou Formation to Qingshankou Formation. The gas-generation threshold depths of mudstone and coal are nearly 2 100 m and 1 750 m, corresponding to the vitrinite reflectance of 0.7% and 0.6% respectively. The cumulative gas generation amounts are 201.37 × 10^11 m^3 and 88.39 × 10^11 m^3 respectively. The average gas-generation intensities of the mudstone and coal are 250 × 10^8 m^3 / km^2 and 100 ×10^8m^3/km^2 respectively. The natural gas methane carbon isotopic value of Yingcheng Formation is between the cumulative carbon isotopic value of mudstone-formed methane and coal-formed methane in Xushen 1 well, which shows that hydrocarbon source rock is similar to coal measures strata of Shahezi Formation and the accumulation is a long-term in the gas pool.