Systems, computer implemented methods, and program products to determine approximate static well pressures for one or more arbitrary shaped wells by estimating the drainage volume of the one or more wells, are provided. The drainage volume of the one or more wells, for example, can be estimated from the one or more computed fluid flow flux vectors, and the approximate static well pressures for the one or more wells can be subsequently calculated by taking the pore volume average of the dynamic grid block pressures within the drainage volume of the one or more wells. The one or more fluid flow flux vectors can be calculated at each iteration in a numerical reservoir simulator as a part of standard simulator computations, negating a need for additional, extraneous computations to calculate effective drainage volume of the one or more wells.