湖相细粒沉积岩成分对可压裂性的控制作用

Controling effect of lacustrine fine-grained sedimentary rocks composition on fracability

湖相细粒沉积岩的成分普遍存在差异,这种差异使得岩石在可压裂性的控制规律上存在明显的不同.本论文以岩石力学实验为基础,对我国东部中新生界湖相细粒沉积岩的可压裂性进行评价,认为细粒沉积岩的可压裂性随长英质矿物或碳酸盐矿物含量的增多均呈先减弱后增强的趋势.黏土矿物和有机质含量增多一般会降低细粒沉积岩的可压裂性,但随成岩作用增强,塑性较强的高岭石和蒙脱石向硬脆性较高的伊利石和绿泥石转化,岩石的脆性增强,可压裂性变好.研究结果表明:长英质矿物或碳酸盐矿物的质量分数小于30%时,可压裂性与该矿物含量呈负相关或相关性较弱;质量分数高于30%时,呈良好的正相关.钙质生物碎屑对裂纹的扩展具有促进作用,而长英质颗粒和以微晶或细晶形式发育的碳酸盐矿物则会为阻碍裂纹的单向扩展,使裂纹尖端方向容易发生偏转,利于发育复杂有效的网状缝而提高细粒沉积岩的可压裂性.

The composition of lacustrine fine-grained sedimentary rocks is generally different in terms of its controlling effect on rock fracability.Based on mechanical experiments,the fracability of the Mesozoic and Cenozoic lacustrine fine-grained sedimentary rocks in eastern China was evaluated.It is considered that the controlling effect of felsic minerals and carbonate minerals on the fracability of fine-grained sedimentary rocks is basically the same.With the increasing of mineral content,the fracability has a trend varies from decreasing to increasing.The increment in clay minerals and organic matter content can lower the fracability.However,with the reinforcement of diagenesis,kaolinite and montmorillonite with strong plasticity was changed into hard and brittle illite and chlorite,which causes the enhancement of brittleness and better fracability for fine-grained sedimentary rocks.Results show that the fracability has a negative or weak correlation with the mineral content when the mass fraction of felsic minerals or carbonate minerals is less than 30%,but has a positive relation when the mass fraction is higher than 30%.Calcareous biodetritus can accelerate the crack propagation,while felsic granule and carbonate minerals developed in the form of crystallite or fine grain essentially act as a hindrance to crack propagation,which makes the crack tip easy to spin,and helps to develop complex and effective mesh joints to improve the fracability of fine-grained sedimentary rocks.