Ultra-Lightweight Proppant Development Yields Exciting New Opportunities in Hydraulic Fracturing Design

Abstract

Abstract Recent research involving the modification of the mechanical properties of particles has resulted in the development of new materials which have particle strengths suitable for application as fracturing proppant yet, possess much lower apparent specific gravity than today's commercial proppant products. For example, whereas the apparent specific gravity of commonly used Ottawa sand is 2.65 g/cc, various embodiments of the new proppant materials range from 1.25 to 2.0 g/cc. Options for proppant selection have previously been limited to identifying the product of median particle diameter to avoid bridging and, sufficient particle strength to withstand the fracture closure stress, thus providing high proppant pack permeability. Fracturing fluids have been selected primarily based upon in-situ rheological properties in an effort to insure proppant placement by providing sufficient viscosity to minimize proppant settling. Treatment pumping rates are limited by the wellbore configuration, the cumulative cross-sectional perforation area and, the desire to keep the fracture ‘in zone’. As the reservoir properties are fixed and the proppant variables dictated by the wellbore and reservoir stress environment, the fracturing practitioner was left with only limited control of two input variables, significantly limiting creative optimization of the stimulation treatment design. Many potential benefits of application of the new ultra-lightweight proppant in hydraulic fracturing treatments are readily apparent. These include substantially reduced proppant settling, allowing the potential for much increased effective propped length, for fluids of lower viscosity and/or, for reduction of pumping rates. The development of the ultra-lightweight proppants is perhaps most exciting from the perspective of the stimulation design engineer, owing to the enhanced options afforded him or her to improve well stimulation. The design engineer is provided not only a new parameter to influence design, but given freedom from the previous limitations imposed on the fluid and treating rates by the high density proppants previously employed. The objective of this paper is to identify those new opportunities afforded the stimulation design engineer, due to availability of these new ultra-lightweight proppants. Numerous fracture modeling runs have been conducted varying fluid density and rheological properties, treating rates (Reynold's Number), proppant density and size. The results of these efforts are provided, and compared in terms of created fracture geometry, propped fracture length, propped fracture surface area, settled proppant height, and fracture conductivity. The data clearly illustrate that the use of ultra-lightweight proppant allows for optimization of fracturing treatments with greatly improved effective fracture length and more importantly, well producibility. Background During the mid-nineties, research aimed at developing deformable particle technology for sand flowback control began to yield materials having unique properties. These materials were significantly lighter than conventional proppants, and were found to exhibit surprisingly high compressive strength. Also, the fact that some of the materials are deformable to begin with, causes them to generate somewhat different behavior in a typical retained conductivity test, from a more conventional proppant. The standard failure envelope does not adequately model performance of these ultra lightweight (ULW) deformable materials since they do not crush in the conventional sense. Rather, they compress until such time as they have no conductivity remaining, by contrast to conventional proppants, in which crushing generates fines that occlude pore space thus impairing conductivity.