Imbibition of water into the shale matrix is known as the primary reason for inefficient water recovery after hydraulic fracturing treatments. The hydration of clay minerals may induce microfractures in clay-rich shale samples. The increased porosity and permeability due to induced microfractures has been considered to be partly responsible for 1) excessive water uptake of gas shales, and 2) increase in hydrocarbon production rate after prolonged shut-in periods. To test this hypothesis, it is necessary to measure imbibition-induced strain and stress under representative laboratory conditions. In this study, we conduct laboratory tests to 1) measure the strain and stress induced by water imbibition in gas shales and 2) investigate the effect of confining load on the rate of water imbibition. We conduct a three-phase study on rock samples from the Horn River Basin (HRB) and the Duvernay (DUV) Formation, located in the Western Canadian Sedimentary Basin.
Kalyanaraman, Nishkriya (The University of Kansas) | Arnold, Cameron (The University of Kansas) | Gupta, Aadish (The University of Kansas) | Tsau, Jyun Syung (The University of Kansas) | Barati, Reza (The University of Kansas)
CO2 foam for enhanced oil recovery applications has been traditionally used in order to address mobility control problems occur during CO2 flooding. However, the supercritical CO2 foam generated by surfactant has a few shortcomings such as loss of surfactant to the formation due to adsorption, and lack of a stable front in the presence of crude oil. These problems arise due to the fact that surfactants dynamically leave and enter the foam interface. We discuss the addition of polyelectrolytes and polyelectrolyte complex nanoparticles to the surfactant solution in order to stabilize the interface using electrostatic forces with a view to generate stronger and longer lasting foams.
An optimized ratio and pH of the polyelectrolytes was used to generate the nanoparticles. Thereafter we studied the interaction of the polyelectrolyte-surfactant CO2 foam and the polyelectrolyte complex nanoparticle-surfactant CO2 foam with crude oil in a high pressure, high temperature static view cell. The nanoparticle-surfactant CO2 foam system was found to be more durable in the presence of crude oil. Understanding the rheology of the foam becomes crucial to determine the effect of shear on the viscosity of the foam. A high pressure high temperature rheometer setup was used to shear the CO2 foam for the three different systems and the viscosity was measured with time. It was found that the viscosity of the CO2 foams generated by these new systems of polyelectrolytes were slightly improved than the surfactant generated CO2 foams. Core flood experiments were conducted in the absence and the presence of crude oil to understand the foam mobility and the oil recovered. The core flood experiments in the presence of crude oil show promising results for the CO2 foams generated by nanoparticle-surfactant and polyelectrolyte-surfactant systems. This paper also reviews the extent of damage if any, that could be caused due to the injection of nanoparticles.
Bose, Charles Chempakathinal (The University of Kansas) | Alshatti, Bader (The University of Kansas) | Swartz, Levi (The University of Kansas) | Gupta, Aadish (The University of Kansas) | Barati, Reza (The University of Kansas)
Guar-based fluids are commonly used as fracturing fluids to form a filter cake, propagate the fracture and carry proppants during a typical hydraulic fracturing job. High viscosity during injection and degradation afterwards are the characteristics of a high quality fracturing fluid that can maintain a highly conductive fracture during production. In order to achieve a conductive fracture, cross-linkers and breakers are added to the fluid. Filter cakes form on the faces of the fracture during injection causing a major pressure drop between the fracture and the reservoir during the production. Degradation of filter cakes formed on fracture faces has been accomplished using chemical breakers Enzymes and oxidizers are the two main classes of breakers. Enzyme breakers have many advantages over chemical oxidizers: they are cheap, are not consumed during their catalytic reaction with guar, react only with the polymer, are environmentally benign, easy to handle and do not damage wellhead equipment.
Different methods of injecting high concentration breakers are still not capable of degrading the residues left after the fracturing jobs. Permeability reduction of proppant pack due to gel residues, width loss caused by the unbroken gel on fracture face and length loss caused by incomplete degradation of filter cake near the tip of the fractures have been previously reported. It has been previously proven that polyethylenimine-dextran sulfate (PEI-DS) nanoparticles can delay the release of enzymes which reduce the viscosity of cross linked guar. This delayed release can be advantageous in order to inject higher concentrations of enzymes by encapsulating the enzyme inside nanoparticles. However, performance of these nanoparticles in reaction with high concentration filter cakes has not been studied yet.
The main objective of this work is to study the feasibility of using polyelectrolyte complex nanoparticles as enzyme breaker carriers and fluid loss additives to be used for hydraulic fracturing applications. Specifically, the fluid loss prevention and clean-up capabilities of the nanoparticle system for fractures propagated in tight formations are studied.
Static fluid loss tests showed a significant reduction, caused by PEC nanoparticles, in both fluid loss coefficients and fluid loss volumes of tight core plugs with permeability values within the 0.01-0.1 mD range.
Fracture conductivity tests, both fluid loss and clean-up, were conducted using HPG gel, HPG gel mixed with enzyme, and HPG gel mixed with enzyme-loaded nanoparticle systems and the results were compared with the baseline conductivity of the system. Significant improvement in the retained conductivity of the proppant pack was observed using the enzyme-loaded nanoparticle system.