A model accounting for more than 30 parameters of drilling projects, and a computer program to enumerate groupings of the wells of a pad with consequent calculations of technical-economic characteristics, are developed and tested. Seven drilling scenarios for a 24-well pad with different starting oil flow rates for the wells are studied. Optimal well groupings in terms of Net Present Value (NPV) for three discount rates and five oil production decline rates have been found. The results show

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... : NPV-maximizing well pad designs with unequal (varying) numbers of wells in groups (clusters) may require only slight alterations of existing designs (changing the configurations of a couple of well clusters); relative NPV gain is inversely proportional to the absolute value of NPV; observed increases in NPV in groupings with varying numbers of wells reach up to 1% with respect to groupings with equal (constant) numbers of wells in groups for conventional projects, and could reach 2% and more for shale formation development projects, and up to 45% for marginal projects.