Improved Hydrocarbon Recovery Using Mixtures of Energizing Chemicals in Unconventional Reservoirs

Summary The objective of this work is to design and evaluate an effective blend of chemicals that can be injected into shale (black oil or critical fluid) reservoirs to enhance hydrocarbon recovery. The blend can be implemented as a prepad fluid ahead of hydraulic–fracturing fluid or as a remedial fluid later in the life of a well. A chemical blend (CB) consisting of an organic solvent (OS), a surfactant, and an oxidizing agent (OA) (in conjunction with an acid) was designed, developed, and tested in the laboratory on crushed rocks, core plugs, and fractured cores to evaluate the interactions of the chemicals with the shale samples. Microcomputed–tomography (micro–CT) scanning, scanning electron microscopy, and Brinell hardness tests were used to evaluate surface changes in the shales. The results of laboratory experiments demonstrate that the CB extracts up to 30% of mobile oil in crushed rocks and improves permeability by 25 to 100% in thin core plugs. Some of the mechanisms that might support the CB application are as follows: (1) pressurization of the formation and reopening of the closed fractures, thus improving well productivity; (2) extraction and mobilization of low–mobility oil, remnants of the original kerogen, removal of deposited salt, and trapped water in matrix and fracture network that impedes fluid flow; (3) creation of pathways to high–pressure liquid–rich small organic pores, where hydrocarbon liquids are trapped, adsorbed, and dissolved in the kerogen; (4) creation of flow pathways for the intrusion of aqueous–based fluids in oil–wet organic–rich rocks with wettability alteration to accelerate the injection, countercurrent imbibition, and osmotic processes; and (5) enhancement of porosity and permeability of fracture surfaces by the introduction of a delayed reaction mechanism to deliver acids deeper into the microfracture network without compromising rock mechanical properties. The presence of sulfate ions in the OA did not contribute to any noticeable scale deposit while delaying the reactivity of acid with inorganic components of shale surfaces. Several field trials have been conducted successfully in the Eagle Ford (EF) Formation.