Abstract: The present disclosure provides a novel process of using nonionic surfactants in wells at, near, or below, their cloud point temperature for increased oil production from reservoir formations. Adjusting the surfactant cloud point temperature to be proximate to the reservoir temperature results in the maximum surface activity of the surfactant, increased adsorption, and better imbibition performance. The nonionic surfactants may be mixed with a solution on surface and then injected into formation brine for spontaneous brine imbibition and crude oil production from oil-wet unconventional reservoir formations. Also disclosed is a surfactant selection process that comprises initial surfactant screening, surfactant persistence tests, and spontaneous imbibition experiments to evaluate the performance of both ionic and nonionic surfactants in altering rock-oil wetting properties and improving oil recovery.

Abstract: The invention relates to assisting the recovery of petroleum from vertically fractured formations utilizing carbon dioxide gas to lower the interfacial tension between the gas and the petroleum in the vertical fractures and in the formation matrix adjacent the vertical fractures to cause vertical drainage of the petroleum down the fracture system. The invention also includes a method for identifying vertically fractured formations which may be particularly susceptible to such recovery with carbon dioxide gas using the capillary to gravity ratio (1/N.sub.B) to select formations having a value for such ratio of 0.2 or less.