This is the science of designing a method for wellbores to produce from the surrounding reservoir rock. The general objective is to safely "complete" a well through perforations or some other means that provides maximum production at minimum cost. With advent of extended latterals the completions technique of hydraulic fracturing has grown to dominate both costs and production of onshore wells. Reference: SPE 0161
Completions engineers design and implement procedures to complete wells as safely and economically as possible. They work closely with the drilling engineers, service contractors, and compliance personnel, as well as with geologists and other technical specialists. The completions engineer has the responsibility for ensuring that costs are minimized while getting information to evaluate the formations penetrated, protecting the health and safety of workers and other personnel, and protecting the environment.