RIASSUNTO
Abstract
The goal of this work is to design and evaluate an effective blend of energizing chemicals that can be injected into shale (black oil or critical fluid) reservoirs to enhance hydrocarbon recovery. The blend can be implemented as the pre-pad fluid ahead of hydraulic fracturing fluid or as a treatment fluid later in the life of a well. As a means to increase recovery, an energized chemical blend (CB) consisting of an organic solvent, a surfactant, an oxidizing agent (and acid) was designed, developed and tested on crushed rock, core plugs and fractured cores in the laboratory to evaluate the interactions of the chemicals with the shale samples. Micro-CT scanning and scanning electron microscopy were used to visualize morphological changes in the shale. A pilot was designed in an existing pad with stable production so that the benefits could be quantified on production rate and recovery.
The results of laboratory experiments demonstrate that the chemical blend extracts up to 30% of mobile oil in crushed rocks and improves permeability by 25-100% in thin core plugs. Some of the factors that support the success of the chemical blend application are: I- Pressurization of the formation and reopening of the closed fractures, thus improving the well productivity, II- 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, III- Creation of pathways to high-pressure liquids-rich small organic pores, where undersaturated hydrocarbon liquids are trapped, adsorbed and dissolved in the kerogen, IV- Creation of flow pathways for intrusion of aqueous based fluids in oil-wet organic rich rocks with wettability alteration to accelerate the injection, counter-current imbibition and osmosis processes, V- Enhancement of porosity and permeability of fracture surfaces by 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 oxidizing agent did not contribute to any noticeable scale deposit while delaying the reactivity of acid with inorganic components of shale surfaces. Laboratory and field pilot results are employed to calibrate a discrete fracture network (DFN) model of the pilot well and the surrounding Eagle Ford formation. The model is used to design and optimize CB injection in future applications.