Abstract: Nonlinear deformation can be used to separate from strain and rotation in process of deformation by means of its method of sum resolution, set up displacement function, calculate mean rotation angle, a representative value of the rotation and show the growth level and the extension direction of the structural fractures by the angle's changes in plane. In Block Min 15-18 located in north part of Minqiao fault anticline in Jinhu sag in Subei basin, multi-bedding volcanic reservoir in Funing formation of Palaeocene has been found, dominated by fissure/fracture in reservoir pore space. The calculated results show that the fissure/fracture-developed areas occur in the east, middle and west parts of the fault block, with fracture orientations of NWW, EW and SN, which are proved by the oilfield development status.

Key words: nonlinear deformation, mean rotation angle, fracture, fissure, volcanic rock