The Investigation On The Influence Of Dispersed Clay On The Acoustic Velocity Of Sands And Determination Of Its Content

There are many factors affecting the acoustic velocities of the sandstone such as porosity,compaction,cementation,clay content,clay distribution and fluid type.Among the above factors,the influence of the clay distribution on the velocities has rarely been reported.Thus,it's necessary to study the influence of the distribution of the clay and the mechanical behavior of the clay on the velocities of the sandstones.In this paper,the pore-filling clay is divided into dispersed clay and contact clay according to the mechanical behavior and the specific distribution.Different clay distribution will cause different effects on the acoustic velocity.The effects of structural clay,laminar clay,dispersed clay and contact clay on the elastic wave velocity have been studied based on rock physics modelling.The results show that the influence of clay distribution on the elastic wave velocity could not be neglected.The analysis shows that the influence of dispersed and contacted clay on the elastic wave velocity mainly depends on the existence of cementation.The influence of cementation on the elastic wave velocity of sandstone has been investigated and a method of rock physics model selection based on compaction and cementation is proposed.The difference content of dispersed clay and contact clay have been distinguished based on thin selection and rock physical diagnosis method,respectively.The theoretical verification of artificial sandstone is carried out,and good results are obtained.The prediction error is reduced by 20% based on thin selection and the modified CCT model proposed in this paper.The prediction error of P-wave velocity is less than 10%.This proves that the improved CCT model proposed in this paper has better application effect in determining the content constraint of contact cements.Finally,a qualitative method for distinguishing clay distribution(include structural clay and dispersed clay)based on petrophysical diagnosis is presented.This method could used to determine the clay distribution which could reduce the risk of seismic\logging interpretation and evaluation and improve the accuracy of interpretation.