Experimental Analysis on Influence of Plastic Formation on Characteristics of Fault Development under Extensional Stress

In order to discuss the influence of plastic layer on the structural pattern and fault characteristics in the process of extensional structural inversion, Two sets of extensional sandbox models with different physical properties are designed. Experiment results indicate that the existence of plastic formation in relatively pure quartz sandstone areas leads to the earlier occurrence time of fault, and larger fault distance and extension length under the action of the same extension stress. In the process of extension and inversion, the existence of plastic strata can change the structural pattern of faults, and it is easier to form plastic detachment faults, which plays two main roles. (1) The scale of faults in the upper part of the plastic layer is relatively large, while that in the upper part of the brittle layer tends to form multiple faults with relatively small scale. (2) The number and scale of the faults in the upper part of the plastic layer with opposite tendency to the boundary detachment faults are obviously larger than those with the same tendency, which shows that the plastic layer can restrain the faults with the same tendency as the boundary detachment faults. Therefore, compared with the eastern area of Wushi depression, the existence of plastic strata has a great influence on the characteristics of the development of extensional reverse structural faults, which can provide the necessary theoretical basis for the later oil and gas exploration.