塔里木盆地和田河气田天然气裂解类型

Types of cracking gas in Hetianhe gas field in Tarim basin

秦胜飞 李梅 戴金星 肖中尧 张秋茶

Qin Shengfei Li Mei Dai Jinxing Xiao Zhongyao Zhang Qiucha

和田河气田天然气来自寒武系高-过成熟烃源岩,气田大体上呈长条状东西向展布。和田河气田天然气组分具有随C/C增加C/C变小、碳同位素δC-δC值变化较大、ln(C/C)值变化较小的特点。根据目前惯用的干酪根裂解气和原油二次裂解气判识标准,和田河气田的天然气应属于干酪根裂解气。和田河气田东、西部井区天然气干燥系数、甲烷碳同位素值及二氧化碳含量存在明显的差异。伴随晚喜山期和田河圈闭的形成,干酪根裂解生成的天然气以水溶方式自东部高压区向西部低压区运移,由于甲烷在水中的溶解度大于重烃、δCH溶解度大于δCH、CO在天然气组分中溶解度最大,造成天然气组分和甲烷碳同位素的分馏,使西部井区天然气具有干燥系数偏高、甲烷碳同位素值偏重、二氧化碳含量明显偏高等特点。

Natural gas in Hetianhe gas field,which is distributed in an elongated E-W direction as a whole,have been sourced by the high-and over-mature Cambrian source rocks.The components of natural gas in Hetianhe gas field have the following characteristics: C/C decreases with increasing C/C,variation of carbon isotope value of δC-δC is relatively large,while variation of ln(C/C) value is relatively small.According to the conventional diagnostic criteria of kerogen cracking gas and secondary cracking gas from oil,the gas in Hetianhe gas field should be of kerogen cracking gas.The dry coefficients,methane carbon isotope values and CO contents of natural gas are obviously different in the western and eastern wellblocks of Hetianhe gas field.Accompanying the formation of Hetianhe trap in late Himalayan,the kerogen cracking gas migrated from the high pressure zone in the east to the low pressure zone in the west in the form of dissolved gas.The solubility of methane in water is larger than that of heavy hydrocarbons,the solubility of δCH is larger than that of δCH),and CO has the largest solubility among the components of natural gas,all these would lead to the fractionation of natural gas components and methane carbon isotope.As a result,the natural gas in the western wellblock is characterized by larger dry coefficient,heavier methane carbon isotope and obviously higher CO content.

10.11743/ogg20050410