胶结物对深水扇含气砂岩地震响应特征的影响

Effect of cements on seismic response of gas-bearing sand in deep-water fan

成岩作用的变化会影响砂岩的岩石物理性质,进而使其地震响应特征发生变化,对于含气砂岩储层,则会干扰对孔隙度和含气性的地震解释。胶结程度是影响砂岩岩石物理性质的重要成岩因素,以珠江口盆地深水扇含气砂岩为例,通过对薄片、测井数据的分析,认为不同钻井处的含气砂岩,其胶结物含量有所不同。根据研究区砂岩特征,选用可以描述胶结物含量变化的接触胶结模型,建立了岩石物理模型,分析了地震响应与胶结物含量变化的关系,证明了胶结物含量的差异正是造成研究区含气砂岩地震响应变化的主要原因。基于以上认识,将研究区划分为强溶蚀—弱胶结、弱溶蚀—强胶结2个成岩相,提出以成岩相的不同,分区域开展含气性地震解释,在强溶蚀—弱胶结成岩相内,含气砂岩顶面为强振幅"亮点"型三类AVO异常,在弱溶蚀—强胶结成岩相内,含气砂岩顶面呈较弱振幅的三类AVO异常,没有明显的"亮点"特征。

The change of diagenesis will affect the rock-physics properties of sandstone,and then affect its seismic response.For gas-bearing sandstone,the change of diagenesis will interference the seismic interpretation of porosity and fluid.Cementation is one of the important diagenetic factors that influence the rockphysics properties.As an instance of the influence of cementation,we studied the deep-water fan sandstone of Pearl River Mouth Basin by analyzing slices,logs and seismic.We found that the content of cements in gas bearing-sandstone of ZJ Formation is different at different wells.In order to study the relationship between cements and seismic response,we used the contact-cement model to simulate the rock physics properties of gas-bearing sand according to its features from drilling data,and proved that the difference of cement volume in sandstone is the main course of the seismic response variation.We divided the study area into two diagenetic facies according to the cementation：Strong dissolution-mild cementation facies and mild dissolution-strong cementation facies.We suggested to use different interpreting methods in different diagenetic facies when carry on gas detection.In strong dissolution-mild cementation facies,the seismic response at the top interface of gas layer is high amplitude and classⅢ AVO anomaly;in mild dissolution-strong cementation facies,the seismic response presents comparatively low amplitude and classⅢ AVO anomaly.