1. A method of injecting a fluid into a subsurface formation, comprising: obtaining data including an initial set of formation parameters related to a subsurface formation and an initial set of operational variables related to an injection well in the subsurface formation; determining a regime of operation for the injection well using a heuristic model, the heuristic model being derived from data points correlated to various regimes of operation; wherein the determination is based at least in part on the obtained data; and wherein the heuristic model indicates whether the regime of operation is in a formation fluidization regime, a formation fracture regime, or a matrix injection regime; and identifying designed operational variables for conducting injection operations based at least in part the determined regime of operation.