1 : A method for assessing an inflow performance relationship (IPR) for a horizontal well in heterogeneous solution gas drive reservoirs, comprising: inputting permeability values of a heterogeneous reservoir; determining spatial variability of the heterogeneous reservoir based on the permeability values, wherein determining the spatial variability of the heterogeneous reservoir includes inputting a value for a number of pairs of permeability values at a predetermined distance apart, determining a summation including logarithms of the permeability values, and dividing the summation by a value equal to twice the number of pairs of permeability values; determining a spatial correlation of the permeability values as a semi variogram defined as: γ ( h ) = 1 2 n ( h ) ∑ i = 1 n ( h ) [ log ( k ) i + 1 - log ( k ) i ] 2 where n (h) is a number of pairs of permeability values at a lag distance h apart and k represents a permeability value at i or i+1; measuring a bottom hole pressure of the horizontal well; and determining a production rate of the horizontal well based on a bottom hole pressure and the determined spatial variability.