Formation damage may be caused by in-situ emulsions, changes in wettability and by deposition of asphaltenes, wax and scales. It is widely recognized that these damage mechanisms may be removed by using microemulsion technology, resulting in enhanced productivity of oil and gas wells. It is also known that microemulsion systems are composed of surfactants, oil, brine and optional co-surfactants and acids. These systems can be very complex, due to the number of variables that influence formulation behavior, including temperature, type of oil, type and concentration of salt, surfactant, co-surfactant, and acid. The development of microemulsions for specific oilfield applications requires a systematic study of phase behavior as a tool to select a treatment composition that satisfies specific parameters defined by the application. Phase behavior studies are necessary in order to identify microemulsion phase boundaries. Phase behavior diagrams of microemulsion systems developed for wellbore damage remediation considered the following variables: temperature, type and concentration of co-surfactants, type and concentration of brine, oils, surfactants and acids. Laboratory studies of surfactant-oil-brine systems used successfully in the field confirm that they undergo phase transitions from Winsor I (oil-in-water with excess oil), to Winsor III (microemulsion), to Winsor II (water-in-oil with excess water). This paper presents formulations positioned in an area of the phase diagram that correspond to maximum detergency and optimum interfacial properties required for field applications. The relationship between phase diagrams, interfacial properties (interfacial tension and contact angle) and well productivity are discussed.