Comprehensive Evaluation of Shale EOR Methods

In today's world as the demand for energy increases, many petroleum companies have introduced more and more use of enhanced oil recovery techniques. The techniques range from low salinity water injection to foam to carbon dioxide gas in the form of huff and puff and flooding, and they are especially useful in shale gas and shale oil reservoirs. Shale reservoirs typically have a low primary recovery due to low permeability and porosity values. EOR methods can significantly increase microscopic and macroscopic efficiencies in shale reservoirs, which can improve oil/gas recovery. EOR methods are generally fit into three separate categories gas injection, chemical injection, and thermal methods. The main type of EOR involving gas is the CO2 injection method, this involves introducing carbon dioxide into the reservoir to change the properties of the oil or gas. Because of low minimum miscible pressure(MMP), CO2 relatively easily combines with oil and gas in reservoirs and is a substance that will lower the interfacial tension and viscosity of hydrocarbons allowing more of them to flow towards the wellbore, hence more recovery. As a solvent, CO2 can also combine with oil and remove some lighter hydrocarbons to escape from the Shale reservoir. The chemical side of EOR primarily in shale reservoirs focuses on surfactant injection. These surfactants can change the overall wettability of a rock, which can increase overall recovery. Most of the time, this is used in “oil-wet” reservoirs, or reservoirs consisting of rocks that will have a higher interfacial tension will hydrocarbons than water. Surfactants can change the oil-wet reservoirs to more of water-wet or intermediate-wet reservoirs, doing this will allow for a lower residual oil, which in turn will mean less oil is trapped inside. Finally, thermal methods are typically used in the case of huff and puff and in some cases the injection of hot water or steam. All these methods can improve overall recovery of oil or gas.In this study, we analyze all the published studies of EOR methods in shale reservoirs to summarize the the applicability of enhanced oil recovery methods in different reservoir conditions. These studies included field applications, lab experiments, and some numerical simulations, which we can analyze the results to determine which methods work better for certain shale reservoirs. Overall the idea is to create a system to base future shale reservoirs EOR strategy design.