琼东南盆地松南低凸起天然气水合物储层特征及勘探潜力

Characteristics and Exploration Potential of Gas Hydrate Reservoir in Songnan Low Uplift,Qiongdongnan Basin

琼东南盆地深水区油气资源丰富,可为水合物成藏提供充足的气源条件,并且油气运移条件良好,可提供流体的疏导通道,此外,深水区海底沉积层的温度和压力满足水合物的形成要求,具备了水合物聚集成藏的条件,成为近年来水合物勘查的重要靶区。为了表征琼东南盆地深水区松南低凸起水合物成藏特征及明确水合物的勘探方向,首次将随钻测井技术尤其是随钻电阻率成像测井技术引入对天然气水合物的识别、赋存状态、成藏序列及勘探潜力的研究中,并首次采用了密度核磁共振相结合的方法计算天然气水合物饱和度。结果表明,琼东南盆地深水区松南低凸起水合物层段具有电阻率高及声波速度快的特征,在纵向上识别出了浅层分散状和深层薄层状2个天然气水合物发育层段。分散状天然气水合物饱和度较高、分选较差、具有一定的非均质性,薄层状天然气水合物饱和度较低、分选差、非均质性强;由于不同赋存状态的天然气水合物均具有一定的非均质性,因此,利用密度核磁共振相结合的方法计算的天然气水合物饱和度不确定性较低,更加贴近地下的真实状态。研究区天然气水合物显示较好的井位,均位于研究区的东南方向,且研究区东南方向存在气烟囱,因此,松南低凸起东南方向为天然气水合物的主要勘探目的区域。随钻测井数据的综合应用,达到了琼东南盆地深水区松南低凸起天然气水合物储层精细表征的目的,为琼东南深水区天然气水合物的整体评价、目标优选和井位方案的设计提供了强有力的参考依据。

Deep water area of Qiongdongnan basin is rich in oil and gas resources,which can provide abundant gas source for gas hydrate accumulation,and effective oil/gas pathways can provide channels for fluid migration.In addition,the temperature and pressure of the sedimentary layer in the deep-water area meet the requirements for gas hydrate accumulation.As a result,conditions for gas hydrate accumulation exist in Qiongdongnan area,which has become the main target for gas hydrate exploration in recent years.In order to characterize gas hydrate reservoir and to identify the exploration potential of gas hydrate in Songnan low uplift area,Qiongdongnan basin,logging while drilling(LWD)data,especially LWD resistivity imaging logging data are utilized for the study of hydrate identification,occurrence mode,accumulation sequence and exploration potential for the first time.Gas hydrate saturation is calculated by density-nuclear magnetic resonance method for the first time.The results show that gas hydrate reservoir of Songnan low uplift in the deep-water area of Qiongdongnan basin is characterized by high resistivity and fast acoustic velocity,and the shallow dispersed and deep thin-layer hydrate reservoir are identified vertically in the study area.The dispersed gas hydrate has the characteristics of high saturation,poor sorting and heterogeneity,while the thin-layer gas hydrate is characterized by low saturation,poor sorting and strong heterogeneity.Because of the heterogeneity identified in different hydrate occurrence modes,the gas hydrate saturation calculated by density-nuclear magnetic resonance method is closer to the real state of the underground with less uncertainty.The gas chimney is speculated to exist in the southeast direction of the study area,which is the main exploration target area of gas hydrate.The comprehensive application of LWD data not only achieves the purpose of fine characterization of the gas hydrate reservoir in Songnan deep water area of Qiongdongnan basin,but also provides strong reference for the overall evaluation,target optimization and well deployment of gas hydrate reservoir in the future.