To find the total pressure difference from the injection well to the production well, Δ𝑃 𝑡𝑜𝑡 , Equation 6 must be doubled. The viscosity, 𝜇̅ , and density, 𝜌̅ , are effective values within the entire reservoir. Also, the well perimeter in this one-dimensional Cartesian space is a square, where each side of the square has a length of 2 • 𝑥 0 . Thus, it is possible to equate the perimeter of the square with the perimeter of a circle with diameter, 𝐷, to yield Equation .