琼东南盆地松南低凸起天然气水合物储层精细表征及勘探方向预测

探讨南海北部琼东南盆地松南低凸起浅层天然气水合物发育情况及水合物的主要勘探靶区。利用随钻测井数据,尤其是高分辨率随钻成像测井数据对水合物储层特征进行研究,并结合区域资料分析了水合物的主要勘探方向。结果表明,研究区的水合物储层的测井响应特征与深层油气有所不同,主要表现为高电阻率、快声波速度及低核磁孔隙度。结合高分辨率随钻成像技术,确定了水合物的宏观赋存状态有两种,分别是分散状水合物及薄层状水合物,这两种水合物均具有一定非均质性,但分散状水合物饱和度更高,水合物的微观赋存状态主要包括孔隙填充型及骨架支撑型。水合物储层岩性主要为泥质粉砂岩及粉砂质泥岩,压实程度弱,因此储层孔隙度高,较细的颗粒及水合物填充孔隙的特征造成水合物储层渗透率低。研究区沉积环境较为稳定,钻井过程中水合物的分解及水合物形成过程中相态的变化造成水合物层段发育变形层理;微断层和裂缝作为液体和气体的疏导通道,沟通了底部气源及浅层水合物稳定带,诱导缝指示现今最大水平应力方向为北东-南西向。研究区东南方向气烟囱附近的钻井水合物厚度大且饱和度高,应为水合物勘探的主要潜力区。

Fine characterization and exploration direction prediction of gas hydrate reservoirs in Songnan low uplift,Qiongdongnan Basin,South China Sea

Based on the logging while drilling(LWD)data,especially high-resolution imaging logging data,the characteristics of gas hydrate reservoir and the main exploration targets of hydrate in Songnan low uplift area in Qiongdongnan Basin are studied and the fine characterization of gas hydrate reservoir and prediction of exploration potential in Songnan low uplift area are discussed.The results show that the logging responses of hydrate reservoir,such as high resistivity,fast acoustic velocity and low nuclear magnetic porosity,are different from those of oil and gas in deep reservoirs.Application of high-resolution LWD imaging data reveals that there are two occurrence modes of hydrate in the study area,the dispersed hydrate and thin layered hydrate.These two hydrates are heterogeneous,but the saturation of dispersed hydrate is higher than that of thin layered hydrate.Pore filling type and matrix support type are the main microscopic occurrence of hydrate in the study area.The lithology of hydrate reservoir is mainly argillaceous siltstone and silty mudstone with weak compaction degree and high reservoir porosity,while fine particles and hydrate filling pores result in low permeability of hydrate reservoir.The sedimentary environment in the study area is relatively stable,and the water is caused by the decomposition of hydrate during drilling and the change of phase state during hydrate formation.Micro faults and fractures in the reservoir serve as channels for liquid and gas to communicate the gas source at the bottom and in the shallow hydrate stability zone.The induced fractures indicate a NE-SW direction of current maximum horizontal stress.Since the drilling hydrate near the gas chimney in the southeast of the study area has high thickness and saturation,it is more likely the main potential area for hydrate exploration.