鄂尔多斯盆地晚古生代煤层作为气源岩的成烃贡献

Contribution of the Late Paleozoic coal measures as source rocks to hydrocarbon generation in the Ordos Basin

鄂尔多斯盆地中部大气田的部分气源来自于上覆晚古生代煤层,为评价晚古生代煤层作为气源岩的成烃贡献,以盆地晚古生代原煤样和显微单组分热模拟实验结果为基础,利用盆地内292组显微组分含量数据参与计算煤的生烃强度,估算出全盆地晚古生代煤成气原始生成量为(328.82～579.48)×1012m3,中间值为463.20×1012m3,其中边浅部中间值为61.49×1012m3,中深部为401.71×1012m3;在讨论该盆地晚古生代煤的成烃贡献时,重点论述了吸附于煤储层本身、未纳入常规天然气贡献之列的理论吸附气量。结果表明,鄂尔多斯盆地晚古生代煤源岩的排烃系数为82%～90%,煤对气体的吸附容纳能力非常有限,绝大部分煤成气在形成之后都运移到了围岩中。

Some gas of large fields in central Ordos Basin was sourced from the Late Paleozoic coal measures.In order to evaluate the contribution of the Late Paleozoic coal measures to hydrocarbon generation,we performed coal and maceral pyrolysis experiments.Based on the experimental results,292 groups of maceral content data within the basin were selected to calculate hydrocarbon generation intensity.The estimated original gas volume generated by the Late Paleozoic coal measures in the whole basin ranges from 328.82 to 579.48 tcm,with a mean value of 463.20 tcm.The mean volume of original gas generated by the shallower coal measures on the margin of this basin is 61.49 tcm,while that by the deeper coal measures in the central basin is 401.71 tcm.When discussing the contribution of the Late Paleozoic coal measures to hydrocarbon generation,we focused on the theoretical absorbed gas volume that is absorbed in the coal reservoirs.It is concluded that the hydrocarbon expulsive coefficient is 82-90% in the Late Paleozoic coal measurers as source rocks in the Ordos Basin,indicating that the gas absorption capacity of the coal measures was very limited and most of the coal-generated gas migrated into the surrounding rocks.