砂岩侵入体的形成机制分析

Analysis on formation mechanisms of sandstone injectites

砂岩侵入体是指深水沉积砂体受到外界的触发,并在一定条件下形成超压,致使上覆弱渗透性沉积物等围岩发生破裂,砂体以流化和液化的形式向周围沉积物产生侵入。砂岩侵入体的形成过程为形成超压、盖层破裂、产生液化和流化、发生侵入。差异压实、地震引发的液化、流体的加入和压力传递等多种因素都可以使砂岩中形成超压,当地层压力达到并超过破裂压力时,发生水力破裂,或地震引起上覆地层破裂,超压砂岩发生流化,侵入到低渗透围岩中。大量未固结的深水沉积砂岩、低—非渗透层的快速覆盖、形成超压的机制和触发事件是砂岩发生侵入的必备条件。

Sandstone injectites are liquefied and fluidized sand bodies in deep water, which intrude into the surrounding sediments when the hydraulic fracture occurs under certain overpressure formation conditions and some trigger mechanisms. The forming processes associated with the development of sandstone injectites complexs include elevation of pore pressure, hydrofracture of sealing strata liquefaction, fluidization and injection of sand. The formation of pore overpressure is controlled by a number of factors, such as differential compaction, liquefaction caused by earthquakes, injected fluids and transmission of pressure. Once the pore pressure reaches or exceeds the fracture gradient, seal failure takes place, or overburden fracture occurs, which may be caused by earthquakes, and then the sand is fluidized and intrudes into the low permeable rock. Large amount of soft deep water sand bodies, rapidloading of low or impervious sediments, overpressure forming mechanisms and trigger events are necessary to sandstone injectites.