差异性成岩过程对百口泉组砂砾岩岩石物理特征的影响

现有针对储层岩石地震岩石物理性质的研究通常不考虑地质过程的影响，致使研究结果缺乏明确的地质意义，制约了储层地震预测和评价的效果.本文通过对玛湖凹陷百口泉组砂砾岩岩石物理性质的测量，并结合岩石学特征分析及沉积环境的划分，在沉积环境与成岩石作用过程框架下分析岩石物理特征的变化规律.研究结果表明，不同微相砂砾岩初始沉积物矿物组成影响了后期成岩过程，差异性的成岩过程形成不同的岩石微观结构特征.三角洲平原辫状河道与泥石流微相砂砾岩塑性组分含量较高，在机械压实阶段已致密化，成岩作用主要表现为成岩早期的淡水渗滤黏土与火山碎屑蚀变黏土的岩屑颗粒包裹式胶结，具有以塑性黏土作为岩石受力骨架的特征.三角洲前缘砂坝与水下分流河道砂砾岩中刚性花岗岩岩屑、石英以及长石的含量较高，机械压实作用相对较弱，原生粒间孔隙保存较好，同时溶蚀孔隙也较发育；砂砾岩成岩作用表现为从前缘砂坝微相的硅质胶结为主转变为水下分流河道微相的硅质+黏土胶结，具有以刚性石英或石英+黏土作为岩石受力骨架的特征.前缘碎屑流砂砾岩样品则表现为快速堆积的钙质基底式胶结，以钙质胶结物作为岩石受力骨架.由砂砾岩颗粒微观接触特征(胶结特征)所决定的岩石受力骨架控制了宏观岩石物理性质变化规律，表现为具有相同颗粒边界力学特征的微相样品具有一致的速度-密度、纵波速度-横波速度以及孔隙度-速度变化关系，也造成不同微相样品在纵、横波速度比及电阻率值上具有明显的差异，具有分区分布的特征，速度比与电阻率可作为百口泉组砂砾岩储层评价的敏感岩石物理参数.研究结果可为该组砂砾岩储层的测井解释和“甜点”地震预测提供依据，并可作为示例形成在地质过程中研究岩石物理特征演化的新方法.

The influence of diagenetic evolution on rock physical properties of sandy conglomerate of Baikouquan formation

The existing researches on seismic rock physical properties of reservoir rock do not consider the influence of geological process, which leads to the lack of geological significance in rock physical research and restricts the effect of reservoir prediction by seismic methods. Based on the measurement of rock physical properties of the sandy conglomerate samples of Baikouquan formation in Mahu depression, combined with the analysis of petrological characteristics and the division of sedimentary environment, the variation of rock physical characteristics is analyzed in the framework of sedimentary environment and diagenesis process. The results show that the mineral composition of the primary sediment of different microfacies affects the later diagenetic process, and the different diagenetic process forms different rock microstructure characteristics. The braided channel and debris flow microfacies samples in delta plain have high content of plastic components, which have been compacted tightly in the stage of mechanical compaction. The diagenesis is mainly characterized by the continuous coat of fresh water illuviation clay and pyroclastic altered clay in the early diagenetic stage, with the plastic clay as the load-bearing frame. The contents of rigid granite debris, quartz and feldspar in the samples of delta front bar and underwater distributary channel are relatively high, resulting the relatively weak mechanical compaction, high primary intergranular pores and well developed dissolution pores; the diagenesis is characterized by the transformation from siliceous cement of samples of front bar microfacies to siliceous and clay cement of underwater distributary channel microfacies, with the rigid quartz or quartz and clay as the load-bearing frame. The sample of clastic flow of deltaic front shows fast accumulation with calcareous basement cement, with calcareous cement as the load-bearing frame. The load-bearing frame determined by the micro contact characteristics (cementation characteristics) of glutenite particles controls the variation of rock physical properties, which shows that the same microfacies sample with the similar mechanical characteristics of particle boundary has the consistent relationship of velocity versus density, VP versus VS and velocity versus porosity, which also results in the apparent variation of VP/VS ratio and resistivity of different microfacies samples The VP/VS ratio and resistivity can be used as sensitive rock physical parameters for evaluation of Baikouquan formation reservoir. The research results can provide a basis for logging interpretation and "sweet spot" seismic prediction of conglomerate reservoirs, and can be used as an example to form a new method to study the evolution of rock physical characteristics in geological process.