For an infinite conductivity vertical fracture flow (linear flow) flow regime, what is the slope of the pressure change?

• A. One
• B. Two
• C. 0.5
• D. 1.5

Answer: (C)

In this regime the flow within the fracture is effectively one-dimensional along its length, and the pressure disturbance spreads through the fracture by diffusion. For linear flow with infinite conductivity, the pressure change scales with the square root of time, meaning P ∝ t^0.5. On a log-log plot of pressure change versus time, the slope equals that exponent, so the slope is 0.5. This square-root time behavior reflects diffusion-dominated flow in a highly conductive fracture.