Abstract:

The Majiang paleo-reservoir of hydrocarbon formed in the Majiang area,Guizhou Province,is one of the large-scale paleo-reservoirs in the residual units of marine strata in southern China.Affected by multi-stages of tectonic movements and experiencing complicated tectonic evolution processes,a large amount of joints were developed in the strata in the area.Joints are the final representation of surface rocks being reshaped and re-formed by multi-stages of tectonic evolution and stress fields,and can be used to reconstruct stress field status and evolution(transformation) processes as indicators for tracing the stress fields.Actual measurements of joints in different strata in the Majiang area are gathered for a statistical analysis on characteristics,occurrence,and geometries of the joints.The regional geological background as well as the intersecting relationship of joints and their crosscutting relationship with faults indicate that there are five stages of joints developed in the Majiang area. They are,from the oldest to the youngest,the planar X-shaped conjugated shear joints of early stage,X-shaped conjugated shear joints of SEE-NNE orientation,joints of NE,SSE,and near EW orientations,which are the products of the Duyun Movement,early Guangxi Movement,Indo-China Movement,and Yanshang Movement re-spectively.The tectonic stress field of each stage is reconstructed through inversion with joint occurrence.The calculation shows that the principle stress field in the Majiang area had shifted clockwise from SEE to SE,SSE, and finally EW.

Key words: joint, palaeo-stress-field, Majiang reservoir, Majiang area