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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.

Hydraulic fracturing has been proved as a successful technology to increase productivity of ultra-tight shale oil and shale gas reservoirs. Although higher concentrations of polymer were traditionally used for conventional fractures, “linear gels”, “waterfracs”, “slick-water” and ”hybrid” fluids have been typically applied for tight shale plays as we produce from formations with lower permeability and higher brittleness. Fracturing jobs in tight shale plays tend to generate or extend a network of fractures while a bi-wing fracture was typically generated in conventional reservoirs. This network of fractures includes a large network of micro-fractures opened during the injection of fracturing fluids. Small fractures tend to close under closure stress unless a nano-sized proppant with significant stress resistance is injected to keep these micro-fractures opened. Although very high conductivity is not required for very low permeability formations, an open fracture or micro-fracture performs better than a collapsed fracture. Proppants with different mesh sizes of 20/40, 30/50, 40/70, 70/140 and 80/200 with grain diameters ranging from 0.033 inch (0.8382 mm) to 0.0041 inch (104.14 μm) have been used during hydraulic fracturing of tight shale formations. These proppants are large enough to create conductivity in the larger generated or existing fractures but not small enough to penetrate into the existing or generated micro-fractures. This will cause the closure of micro-fractures at the end of a fracturing job thus reduction in the length and conductivity of the complex fracture network. This reduction in the fracture network extension will reduce production from tight shale formations. The objective of this work is to investigate size, nano-hardness, reduced elastic modulus, fluid loss prevention capabilities as well as their induced fracture conductivity by nano-proppants from a currently known waste product. Transmission Electron Microscope (TEM) images showed that nano-proppants had particle sizes varying from 100 nm to 1 μm. Particles showed hardness and reduced elastic moduli of 1.3 GPa and 20 GPa, respectively. These properties show potential for these nanoparticles to be used as proppants to keep fractures open under stress. Fluid loss tests were conducted using 1% (w/w) concentrations of nanoparticles mixed with 2% (w/w) of KCl, cross-linked guar solutions, and cross-linked guar solutions mixed with 1 % concentration of nanoparticles and significant fluid loss reduction was observed for one of several types of nanoparticles. These nanoparticles generated significant conductivity when used as proppants in an API fracture conductivity test. Fracture permeability values of 27-33 mD were generated using these nano-proppants. Use of nanoparticles prior to the placement of larger proppants is recommended in order to prevent fluid loss into the formation, and also increase the conductivity of the fissures and micro-sized fractures.

Hydraulic fracturing is a commonly used practice in the oil industry for well stimulation and production enhancement. With the general theme of the oil and gas industry moving toward systems with nano-sized pores, nanoparticles have gained a significant amount of attention especially in the field of hydraulic fracturing. Several groups have developed different nanoparticle systems that improve hydraulic fracture conductivity. This paper is a review of the highlighted work published in the area of application of nanoparticles to improve fracture conductivity. Nanotechnology can be used to improve the efficiency of hydraulic fracturing process. Four major production challenges faced by the oil and gas industry including incomplete filter cake cleanup, proppant pack damage, formation damage, and having micro-fractures that are not packed with proppants and will close under closure stress are introduced in this work. Solutions have also been reported using the advances in nanotechnology to address some of these challenges.

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