Abstract:

The development of structural fractures and finite strain state are closely related in the oil and gas reservoir. In order to
explore a new method of finite strain analysis and structural fracture prediction, this study designed and performed a set of sandbox
experiments. The particle image velocimetry (PIV) technique was applied to quantitatively analyze the experimental process. The
experimental model was a unilateral indentation model with a viscous layer in the vertical direction, and the results represent a

macroscopic box fold. Using the PIV technique, we can obtain the displacement field data during the deformation process in each stage
of the experiments, calculate the incremental strain in each step, and analyze the finite strain state during the whole deformation
process from the initial stage to the time after the fold was formed. Furthermore, the genesis mechanism and distribution can be
discussed to quantiatively predict the fractures. At the beginning of the deformation, the finite strain was weak (about 4-8%) and
widely distributed. Weak compressive linear strain was represented in the direction of indentation and weak tensile linear strain in the
vertical direction. These phenomena were interpreted as the results of the pure shear deformation, such as the thickening and parallel
shortening of the layers before the folding and faulting initiated. It is also the main mechanism of the formation of the regional tension
fissures and shear cracks. The finite strain was localized in the fault zone and the adjacent area when the fold and fault formed. Strong
shear and tensile shear strain (up to 20%) was revealed. These were the results of the simple shear deformation along the fault plane. It
is also the main mechanism of the formation of the local shear fractures and tensile shear cracks.

Key words: analogue modeling, particle image velocimetry (PIV), finite strain analysis, tectonic fracture prediction