Compaction behavior and characteristics of logging response of deep mudstones of the Mesozoic in the central Junggar Basin
LI Chao
ZHANG Likuan
LUO Xiaorong
LIN Huixi
ZHANG Zhongpei
QI Yukai
BIAN Changrong
ZHAO Yida
Abstract：Clay mineral transformation during deep burial of mudstone is closely related to mi-crostructure,physical properties and pore pressure,which was a major focus of mudstone compaction research.In this paper,the Mesozoic mudstone in the central Junggar Basin was selected as a research object,and based on the X-ray diffraction of clay minerals,the clay min-eral transformation process and its effect on the mudstone compaction behaviour and logging response were investigated.The results show that the clay minerals of the Mesozoic mudstone in the central Junggar Basin are mainly composed of mixed smectite-illite layer(mixed I/S lay-er)and illite,with a small amount of kaolinite and chlorite,and no discrete smectite.The Mesozoic mudstones underwent significant clay mineral transformation in a window with a depth of 4 000～4 800 m and a temperature of 90～105 ℃,with smectite in the mixed I/S layer being rapidly transformed into illite,as evidenced by a decrease in the smectite-to-illite ratio(I/S ratio)and a change in the mixing layer type from R0 to R3.According to the degree of clay mineral transformation,the compaction process of the mudstone was divided into three stages,and it was found that the pore reduction mechanism varied at different stages of com-paction.The effective stress was the main factor in pore reduction in the middle and shallow mechanical compaction stages,while the clay mineral transformation and the effective stress together intensified the loss of porosity in the deep mudstone.Clay mineral transformation leads to a decrease in mudstone porosity and an increase in density,which to some extent alters the response of different logging information to the compaction process,which leading to er-rors in the accurate identification of the compaction stage and the overpressure generation mechanisms.The improved sonic transit time-density cross plot,based on the normal compac-tion trend lines of different compaction stages,can be used to effectively differentiate the com-paction stages of deep mudstone and identify the overpressure generation mechanism.This study helps to deepen the theory of mudstone compaction and has important guiding value for predicting the pressure of deep layers.
Keywords：chemical compactionclay mineralslogging responsesMesozoic formationsJunggar Basin
Publication Date：2025-09-30
Online Publishing Date：2025-10-31(First online date of this platform, not the publication date of the document)
Pages：14( 1123-1136 )