Fluid flow characteristics of cross-fractures with two branch fractures of different roughness controlled by fractal dimension: An experimental study

Abstract

The cross-fracture is one of the basic units of rock fracture network in the deep energy exploitation. The scientific evaluation of the fluid flow behavior of a cross-fracture is a key link in the description of the fluid flow behavior of deep fractured reservoirs. Based on the Weierstrass-Mandelbrot function and combined with 3D printing technology, numbers of cross-fracture models with different roughness levels controlled by the fractal dimension are developed. A new calculation method of the pressure-drop loss coefficient is proposed, and the competitive flow diversion behavior and fluid flow state of the two branch fractures are examined with different water head ratio. The results show that the roughness difference between the cross-fracture branches is the important factor controlling the phenomenon of competitive flow diversion. Cross-flow confluence will result in a notable pressure-drop loss, and with increasing fractal dimension of the branch fracture, a larger pressure-drop loss occurs, and the rough branch fracture obtains a larger flow rate proportion. Besides, the water head ratio condition of the inlets is another important factor for the cross fracture flow. When the pressure ratio between the rough inlet and smooth outlet equals 1, the pressure-drop loss is at its maximum, and the flow rate proportion of the rough branch fracture is at its minimum, and Re gradually increases while Eu clearly decreases with increasing water pressure. When the pressure ratio between the rough inlet and smooth outlet is not equal to 1, the pressure-drop loss, the competitive flow diversion ability of the branch fracture, Re and Eu will greatly change with increasing water head ratio. The results can provide new insights into the flow through a fractured reservoir.