Experiments on Friction and Non-Steady Slip for Shale

L1₁ sub-section shale reservoir is the major production layer in the South Sichuan shale gas block. For the horizontal well production, different well paths in the different layers can show quite big production gap, which may be due to the different shale crushabilities. However, the elastic modulus and brittle minerals for different layers in L1₁ sub-section have not shown much difference, so it is still impossible to evaluate the shale brittleness sufficiently with the conventional methods and models, Based on studies on the cause of earthquake, the steady & non-steady state failure is introduced to characterize the crushability for the different L1₁ layers in this paper. The new friction and steady & non-steady state experiments were designed to replace the conventional fault gauge testing method for the L1₁ outcrop samples. Firstly, the influence of the lamination, mineral constituents and normal stress on the friction for shale was studied and analyzed. Secondly, the steady & non-steady state behavior was characterized and quantified by the calculated ^a-^b value for the shale with different mineral constituents. Thirdly, the critical value from velocity-weakening to velocity-strengthening was established by the overlay method. Taking Well YS108 field in Zhaotong shale block as the example, the different crushabilities for different layers were analyzed and discussed. It is found that L1₁^1-2 layers have better crushability that can cause the shear slide easily and generate the map cracking, while the L1₁⁴ layers have worse crushability that generates the single cracking or cause the shear slide difficultly.