Triaxial testing on water permeability evolution of fractured shale

A sound understanding of the water permeability evolution in fractured shale is essential to the optimal hydraulic fracturing (reservoir stimulation) strategies. We have measured the water permeability of six fractured shale samples from Qiongzhusi Formation in southwest China at various pressure and stress conditions. Results showed that the average uniaxial compressive strength (UCS) and average tensile strength of the Qiongzhusi shale samples were 106.3 and 10.131 MPa, respectively. The nanometre-sized (tiny) pore structure is the dominant characteristic of the Qiongzhusi shale. Following this, we proposed a pre-stressing strategy for creating fractures in shale for permeability measurement and its validity was evaluated by CT scanning. Shale water permeability increased with pressure differential. While shale water permeability declined with increasing effective stress, such effect dropped significantly as the effective stress continues to increase. Interestingly, shale permeability increased with pressure when the pressure is relatively low (less than 4 MPa), which is inconsistent with the classic Darcy's theory. This is caused by the Bingham flow that often occurs in tiny pores. Most importantly, the proposed permeability model would fully capture the experimental data with reasonable accuracy in a wide range of stresses.

Study on the Coal-Water Fuel Pipeline Transportation Taking Into Account the Granulometric Composition Parameters

The highly loaded coal-water fuel pipe flow was verified. The move of the coal-water fuel with the 60% of coal loading practically has not been studied, especially for the coal originated from Ukraine. Through experimental research it was discovered that the water-coal fuel of such concentrations has a Bingham rheological characteristic. The verification was carried out by comparing the results of numerical calculations and experimental research. As a result of the numerical calculations of the flow, near the axis of the tube, a zone of approximately the same velocity is obtained, which qualitatively coincides with the results of experimental studies and with the results of the analytical description of the Bingham flow. As a result of the calculation the pressure drop value was defined, costs and velocity distribution over the cross section of the pipeline in the straight line and in curve. The velocity distribution profiles of the water-coal fuel flow are built. To compare the results of the calculation and to validate the rheological model choice velocity calculations were performed using the proposed model of Bingham and Newtonian fluids at the same effective viscosity values.