Objective In order to clarify the brittleness characteristics of basement metamorphic rock reservoirs in Bozhong 19-6 gas field, Bohai Bay Basin, and provide accurate basic data for the selection of favorable areas in the subsequent exploration and development of this area.

Methods Based on whole rock mineral analysis experiment by X-ray diffraction, geophysical logging data and pre-stack seismic data, The brittleness characteristics of basement metamorphic rocks in Bozhong 19-6 gas field in Bohai Bay Basin were characterized by mineral component method, static rock mechanics parameter method and seismic brittleness inversion method, and the single well and spatial distribution characteristics of brittleness were defined. Combined with physical property test, mercury injection experiment and rock mechanics experiment data, the main controlling factors of brittleness of metamorphic rocks were discussed. The significance of brittleness characteristic of metamorphic rock on fracture development degree and fracturing ability is also clarified.

Results The results show that the brittle mineral component method based on quartz, feldspar, dolomite and calcite and the static rock mechanics parameter method have good applicability to the evaluation of the single well brittleness of the basement metamorphic rock of Bozhong 19-6 gas field. The plane distribution of the metamorphic rock brittleness has strong heterogeneity, and the vertical distribution characteristics are mainly controlled by structural characteristics and weathering. Reservoir physical property, pore radius and burial depth are the main influencing factors of brittleness. Meanwhile, brittleness index has a good positive correlation with fracture development degree and fracturing ability of metamorphic rock.

Conclusions The brittleness evaluation results of the basement metamorphic rock reservoirs in the Bozhong 19-6 Gas Field are of great significance for predicting high-quality fractured reservoirs and optimizing fracturable intervals.