Method for exploiting an underground reservoir, in particular a petroleum reservoir, passed through by at least one first well from which a fluid is produced, wherein a position of at least one second well to be drilled is determined using a map of production indicators, said map comprising a set of cells, each cell being associated with a production indicator defining an impact on the production of the fluid of an addition of a well in this cell, characterized in that it comprises the following steps: - said map is constructed by means of the following steps: a) production indicators are determined for a first group of cells of said map, by means of a precise flow simulation over a defined period of time, using a flow simulator and a reservoir model; b) production indicators are determined for a second group of cells of said map, by means of an approximate flow simulation for which at least the following are modified with respect to said precise flow simulation: the defined period of time, the flow simulator or the reservoir model, the modification of the defined time period consisting in a decrease in said period of time, the modification of the flow simulator consisting in simplifying said flow simulator by neglecting certain physical effects during the flow of the fluid and the modification of the reservoir model consisting in decreasing the resolution of said reservoir model; c) said production indicators are interpolated for all of the cells of said map, by means of an interpolation model constrained by said production indicators; and - the position of said second well is defined by the cell in which said production indicator is maximal. - said map is constructed by means of the following steps: a) production indicators are determined for a first group of cells of said map, by means of a precise flow simulation over a defined period of time, using a flow simulator and a reservoir model; b) production indicators are determined for a second group of cells of said map, by means of an approximate flow simulation for which at least the following are modified with respect to said precise flow simulation: the defined period of time, the flow simulator or the reservoir model, the modification of the defined time period consisting in a decrease in said period of time, the modification of the flow simulator consisting in simplifying said flow simulator by neglecting certain physical effects during the flow of the fluid and the modification of the reservoir model consisting in decreasing the resolution of said reservoir model; c) said production indicators are interpolated for all of the cells of said map, by means of an interpolation model constrained by said production indicators; and a) production indicators are determined for a first group of cells of said map, by means of a precise flow simulation over a defined period of time, using a flow simulator and a reservoir model; b) production indicators are determined for a second group of cells of said map, by means of an approximate flow simulation for which at least the following are modified with respect to said precise flow simulation: the defined period of time, the flow simulator or the reservoir model, the modification of the defined time period consisting in a decrease in said period of time, the modification of the flow simulator consisting in simplifying said flow simulator by neglecting certain physical effects during the flow of the fluid and the modification of the reservoir model consisting in decreasing the resolution of said reservoir model; c) said production indicators are interpolated for all of the cells of said map, by means of an interpolation model constrained by said production indicators; and - the position of said second well is defined by the cell in which said production indicator is maximal.