木里冻土区天然气水合物成藏特征  

Reservoir characteristics of gas hydrate in the Muli permafrost region

作　　者：张鹏辉[1] 方慧[1] 白大为[1] 何梅兴[1] 吕琴音 

机构地区：[1]中国地质科学院地球物理地球化学勘查研究所,河北廊坊065000

出　　处：《东北石油大学学报》2018年第1期24-31,76,共9页Journal of Northeast Petroleum University

基　　金：国家高技术研究发展计划(863计划)项目(2012AA061403);国家重点研发计划重点专项(GZHL20110324;GZH201400305);中国地质科学院地球物理地球化学勘察研究所中央财政科研项目结余资金资助项目(JY201705)

摘　　要：为探讨木里冻土区天然气水合物的烃类来源及成藏特征,应用地球化学反演方法,根据碳同位素和成熟度的关系,分析烃类的成因和来源,结合水合物赋存特征、地层埋藏史等研究水合物成藏特征。结果表明:木里冻土地区天然气水合物的烃类气体以油型气为主,浅部混有少量煤成气;前者主要来源于石炭统和下二叠统烃源岩,侏罗系烃源岩贡献较小。水合物成藏空间分布非均质性较强,纵向上不同层段的气体来源和充注特征具有较大差异,上部层段烃类成熟度较低,来源于早期常规油气藏破坏后逸散气体,混有少量水合物分解甲烷;中部层段甲烷具有"多阶"充注特征,有原油裂解气贡献,底部发育油气优势运移路径;下部层段烃类主要来源于深部烃源岩层(早二叠系和石炭系),具有"多阶"充注特征。水合物形成前的常规油气藏演化和水合物形成后的保存条件,是研究区天然气水合物成藏和展布的主控因素。The source of hydrocarbon gas in Muli permafrost region in Qinghai province(e.g well DK-2)is studied based on carbon isotope and maturity(vitrinite reflectance,Ro)relation established by different scholars.The hydrocarbon gas in natural gas hydrate in study area is primarily oil-derived gas,with mixed-gas characteristics of a little coal-type gas in the shallow depth.Based on the basin burial history and carbon isotopic values of methane,the hydrocarbon gas in the hydrate is mainly derived from the Carboniferous and Early Permian source rocks,whereas the upper Jurassic source rocks have less contribution towards hydrocarbon gas.At present,the distribution of gas hydrate reservoir has relatively strong heterogeneity,and distributes locally in the plane.It is divided into three intervals in vertical,the upper interval(A):the hydrocarbon gas is of low maturity,mainly originating from escaping gas after the early stage of reservoir destruction,with mixed-gas of a little methane from hydrate decomposition;the middle interval(B):F2 fault(reverse fault)is the main migration pathway,the methane is characterized by " multi-stage" and has a contribution from oil-cracking gas;the lower interval(C):the hydrocarbon gas is mainly originated from deep rocks(Early Permian and Carboniferous),the methane is also characterized by " multi-stage" filling.The present spatial distribution of hydrate reservoirs is a result of a combination of oil and gas reservoir evolution before permafrost formation(1.2 Ma)and pres-ervation conditions of hydrate reservoirs after permafrost formation.

关 键 词：木里冻土区 天然气水合物 气源 主控因素 成藏模式 

分 类 号：P618.13[天文地球—矿床学]