A process by which vertical fracture growth is controlled downhole in a hydrocarbon producing formation through which a wellbore extends. The wellbore includes a perforated casing. Two different fluids are simultaneously forced along two separate flow paths downhole into the borehole, with the first flow path entering the uppermost perforations and the second flow path entering the lowermost perforations of the perforated casing. The first flow path conducts acid laden with relatively coarse grains of sand into the hydrocarbon producing part of the formation, while the second flow path conducts the flow of water laden with relatively fine grains of sand into the water producing part of the formation. The flow characteristics of the water/sand mixture and the acid/sand mixture causes the fine sand to drop out along the water/oil interface located between the low water and high water part of the formation. This action forms a barrier which forces the acid/sand solution to be forced out into and remain in the low water strata, where the formation is fractured, propped open by the relatively coarse grains of sand, and acidized. This process therefore treats the hydrocarbon containing part of the formation, rather than losing the treatment fluid into the high water part of the formation.