PTA is a Geological tool when we infer hydrocarbon limits. Pressure derivative pattern or trend changes include several characteristics which infer hydrocarbon deposit boundaries or limits. External no-flow boundaries like faults and channel widths are identifiable. High flow conglomerate deposits in contact with low deliverability sand deposits are identified by reservoir Bilinear flow — check well logs for fining up or down signatures. Underlying water legs, active aquifers, and gas caps represent hydrocarbon limits, thus volumetric reserves. Radius-of-investigation calculations help geologists refine their mapping.