Summary In this paper, we discuss proppant transport behavior in a complex slot system. Specifically for this study, focus is placed on two different fluid systems, a water/glycerin solution and a water/sodium chloride solution, which represent varying fluid densities and viscosities. The effects of changing fluid viscosities, fluid densities, proppant densities, proppant sizes, proppant concentrations, and slurry injection rates on proppant transport were then experimentally investigated. The slot system consists of a 4-ft long, 0.2-in. primary slot with three secondary slots and two tertiary slots, all at 90° angles to each other. The fluid systems represented brine fluids up to 9.24 ppg and viscous fluids up to 4.3 cp. Although glycerin was used for viscosification, the results can be compared to fluid systems with similar viscosities that are created using other additives such as friction reducers. The proppants used in the study consisted of two sands of 100 and 40/70 mesh (specific gravity of 2.65) and two 40/70 ceramic proppants with specific gravities of 2.08 and 2.71. The study results show that a water/glycerin solution, with a viscosity of 4.3 cp, has significant proppant-carrying capacity with proppants delivered uniformly to greater distances. In addition, sieve analysis conducted on each of the various slots indicated that for all tested proppants that the water/glycerin systems were more capable of carrying larger particles to farther distances. Conversely, the results show that a water/sodium chloride solution of 9.24 ppg density has less capability to carry the proppant farther into the slots. From a comparison standpoint, in all tested cases, viscosity increases had a greater impact on the overall proppant transport than fluid density. In addition, results of the study showed that both increasing proppant concentrations and injection rates have a positive impact on proppant transport, with more proppant being transported farther into the slot system in both cases. The higher the proppant concentration, the sooner the equilibrium dune height (EDH; height when transport starts to occur after dune building) was achieved, the more efficient transport became. Increasing the injection rate led to improving proppant transport by increasing the drag and lift forces on the proppant, which lead to decreased proppant settling velocities and transport farther into the slots.
3D printing is a type of additive manufacturing technology that allows for digital 3D models to be made into physical objects out of a wide range of thermoplastics, resins, and occasionally metals. In previous years, 3D printing models at high-resolution suitable for oil and gas research was either time consuming, cost-prohibitive, or limited to a small model build volume. However, the rapid advancement in resin 3D printing technology recently has allowed for a significant increase in production speeds and model size at little cost. In this study, we utilized 3D printed rough-wall fracture panels in a large-scaled proppant transport apparatus to evaluate the feasibility of repeatable and realistic experimental investigation by the 3D printing technology. Understanding proppant transport in hydraulically created fractures helps to answer the questions about proppant distribution, resultant fracture conductivity, effectiveness of fracture fluid and additives, and all leads to fracture treatment efficiency. In the past, lab experiments showed that fracture topography plays an important role on fracture conductivity, and the characteristics of fracture surfaces have been grouped as random distribution, channel, wavy and ledge (step-change). These surface features can be described by geostatistical parameters. For large-scale proppant transport, the realistic surfaces are difficult to create, and thus most studies have used smooth-surfaced parallel acrylic panels for the fracture walls. Stereolithography (SLA) resin 3D printers produce a physical model by using an ultraviolet light source to selectively illuminate and cure a photopolymer onto a travelling build platform. The physical models are based on a computer-generated surface with controlled statistical definition. We have successfully printed panels to build a 4ft X 2ft main fracture with a smaller fracture intersecting orthogonally. The panels are carefully printed with transparent resin to allow for video recording. Initial tests showed the mechanical integrity of printed fractures and proppant transport results. This paper describes the detailed procedure of generating fractures by 3D printing, experimental setup and the test results of proppant transport.
The main functions of hydraulic fracturing fluids are to create a fracture network and to carry and place the proppant into the created fractures networks, thus, adding to fracture conductivity. Significant research has been performed to develop ideal fracturing fluid systems. The development focus has mainly been on optimization of a fluid rheology that can transport and place the proppant into the primary and any subsidiary fractures with less damage to the formation and at a lower cost. The main goal of this work is to add to the understanding and optimization of proppant transport in complex hydraulic fracture networks. Specifically for this study, focus is placed on two different fluids, water-glycerin solution and water-sodium chloride solution, representing varying fluid densities and viscosities. The effects of changing fluid viscosities, densities, proppant densities, proppant sizes, proppant concentrations, and slurry injection rates on proppant transport were then experimentally investigated. This experimental work shows that viscosity has a greater impact on the proppant transport than fluid density does, thus implying a larger impact on the resulting fracture conductivity. The results of this work show that a water-glycerin solution, with a viscosity of 4.3 cp, has significant proppant carrying capacity with proppants delivered uniformly to greater distances. On the other hand, the results show that a water-sodium chloride solution of 9.24 ppg density has less capability to carry the proppant deep into the fractures indicating that viscosity has a greater impact on the proppant transport than fluid density does. The lab results also showed that increasing proppant concentrations and injection rates has a positive impact on proppant transport.
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