AbstractThere are many mature oil fields in the North Sea. One of them is the Clair Oil Field, located on the United Kingdom Continental Shelf (UKCS) in Scotland. This oil field is unique because of the results of failure studies of several fluid injections, constituting secondary and tertiary oil recovery techniques, on increasing oil production. Only waterflooding has shown a promising future. In this paper, three-dimensional (3D) numerical simulations investigate the influence of infill drilling optimization by waterflooding in the Clair Oil Field so as to maximize net present value (NPV). An important goal of this study of reservoir management was to determine optimal well locations and optimal operational parameters (production constraints) that maximize cumulative oil production. Theoretical ideas and mathematical models with field data performance demonstrated the factors that can be considered in infill drilling so as to increase oil reserves. Most of the factors were related to reservoir heterogeneities and were important quantitatively for fluid injection and production. The results revealed that the four infill wells added in this study led to an increase in the field’s total cumulative oil production from 7.91×106 to 9.39×106 m3. The NPV after infill drilling optimization by waterflooding increased by 54.4% over the base case. The oil recovery factor rose from 17.2% to 20.2%, while the gas oil ratio (GOR) fell from 1,000 to 840 SCF/STB. After combining infill drilling with waterflooding, the horizontal infill producers outperformed vertical infill producers by 5.5%. The field water cut was reduced from 95% to 88%. In addition, an analysis of cumulative production between parent and child wells was made. It was found that child wells produce less cumulative oil production than do parent wells. This paper reveals the greater success of a combination of infill drilling with waterflooding in enhancing oil production compared to other findings where the influence of infill drilling and waterflooding were analyzed separately or compared. It can be concluded that the Clair Oil Field has great potential to increase oil production by combining infill drilling with waterflooding, after other improved oil recovery techniques fail.