Multi-Physics Models for Proppant Placement in Energy Georeservoirs

University Of California-San Diego, La Jolla CA

Investigators

Abstract

Underground energy technologies are of crucial importance in contemporary geomechanics, including Enhanced Geothermal Systems (EGS). EGS use geothermal energy to produce electricity from hot deep underground permeability-enhanced rock formations. This project addresses the need for more effective proppant (granular material that keeps the fractures open) usage during geothermal energy recovery. Specifically, resolving proppant placement issues will aid optimization, growth and further development of georeservoirs, and will speed up transformation of the EGS technology from its current early development stage to commercial use. This will benefit global renewable energy market and global sustainable energy delivery. This research has also a potential for contributing to quantitative understanding of several additional geomechanical issues, such as mud flows and slurry flows, internal erosion of dams and scouring of soil around structures. This research project advances the knowledge of fundamental physics of flow of dense suspensions, and develops new theories that would improve engineering design for proppant placement into branching hydraulic fractures with irregular, rough surfaces. The models resulting from this activity will, for the first time, capture particle agglomeration by accounting for the interplay between particle-particle interactions and fluid hydrodynamic forces and the role of fluid, particle and fracture properties. Our multidisciplinary team, consisting of a geotechnical engineer and a mathematical modeler, will collaborate with other programs to broaden participation of women and other underrepresented groups in science through research, engineering and educational engagements. This project seeks to better understand and mitigate the conditions resulting in proppant logging during proppant-fluid injection into hydraulic fractures. The project products will lead to efficient proppant placement during permeability enhancement, potentially reducing its environmental impact. The overarching goal of this project is to gain quantitative understanding of this phenomenon and requires development of new mathematical theories. Current practice for predicting proppant flow and transport relies on empirical relationships developed from laboratory tests involving large width, smooth, straight slots, appropriate for use in simplified single-fracture models. However, most hydraulic fractures are rough and branching, which creates a complex path for the fluid and proppant transport. The physics of dense slurry flow and transport includes particle-particle and fluid-particle interactions. Especially for fluids used in proppant placement, this physics is not properly understood and, hence, not adequately accounted for in current models. A mathematical model of proppant flow in realistic fracture networks will be developed, and validated with laboratory-scale experiments. The experimental component comprises next-generation slot-flow experiments in 3-D printed fractures using scanned rock surfaces from fracturing tests. The fractures will be printed with transparent materials, enabling the use of Particle Image Velocimetry (PIV) to track the movement of proppant particles. The project's theoretical part consists of two interrelated components, development of a continuum-scale constitutive law that accounts for particle-particle and particle-fluid interactions, and development of a computationally efficient algorithm for modeling proppant flow in fractures with rough walls and (randomly) varying apertures. The continuum-scale models will be parameterized with parameters reflecting properties of fracture surface's roughness, average fracture width, and physical and mechanical properties of fluid and proppant particles. These and other effective model parameters will be determined from both discrete numerical simulations and slot-flow experiments. The model will serve as a practical tool for reservoir engineers to ensure the proper proppant placement in hydraulic fractures and to predict and plan the reliable permeability enhancement of georeservoirs.