Abstract: The conventional formula for calculation of investigation radius of wells is deduced for vertical wells, which can only be applicable for radial flows rather than for parallel flows. By means of the flow theory in porous media and the production scheme of constant bottom-hole pressure of a production well, the concept of investigation distance of parallel flows is defined. Then the formula of investigation distance of parallel flow is deduced with the propagation theory of pressure pulse wave in formation. This formula can be used for situations of horizontal wells, parallel well patterns and channel strip sands, solving the problems of the pressure propagation scope and the distance of investigation in order to guide the production better.

Key words: production well, investigation distance, parallel flow, radial flow, formula, formation