The Hydraulic Fracturing Field Test (HFTS) project, fielded within the Wolfcamp Formation in the Permian Basin, provides an excellent opportunity to further develop our understanding of the geomechanical response to hydraulic stimulation and associated fluid transport and hydrocarbon production in nano-porous lithologies. The drilling program was designed to elucidate the intra- and inter-well stress interactions within a single horizon and also among vertically separated wells in different lithologic units, and their influence on hydrocarbon production. In addition to a full set of geophysical and other observations, such as microseismic, tilt, downhole pressure variations, tracer transport, and individual stage/perf production data, the HFTS project obtained core samples from wells drilled through the stimulated region. This core provides a unique opportunity to potentially observe and characterize a number of features such as the initiation and propagation of fractures ranging from the primary hydraulic fractures, to reactivation of pre-existing natural fractures and micro-fractures developed in the host rock adjacent to the primary hydraulic fractures. The distribution of these features provides ground truth for the interpretation of geophysical observations. The drill-back samples also provide direct observation of the distribution of proppant, a feature that is otherwise virtually impossible to determine.
Here we describe a multi-scale effort to utilize the HFTS data and HFTS project participants’ expertise and experience to investigate the mechanical and geochemical/hydrologic response of the Wolfcamp Formation. The focus of the investigation will encompass a spatial scale extending from the pore- to reservoir scale. Our primary goals are as follows: (1) Enhance the utilization and integration of HFTS results through the application of advanced computational tools describing geomechanics and pore to core-scale transport, (2) provide 2D and 3D characterization of drill-back material to provide a fundamental framework for simulation multi-scale transport in nano-porous rocks, and (3) utilize HFTS data and focused laboratory experiments on HFTS core samples to validate and improve existing computational tools. It is only by confronting multi-scale experimental data (both lab and field) that the inadequacies of such tools can be assessed. This assessment will result in reformulation and/or addition of underlying physical models and re-evaluation of how pre-stimulation petrophysical data is utilized and upscaled for incorporation in reservoir simulations. The ultimate outcome of this project is the application and validation of a new framework for microscopic to reservoir-scale simulations of hydraulic fracturing and production, built upon a fusion of existing high-performance simulation capabilities available at DOE’s national labs.
The work described will have important impact in terms of developing the Wolfcamp resource, a truly massive unconventional play, the continued development of which will have substantial impact on our nation’s energy security. However, given its focus on fundamental properties and processes, the project’s impact will be more far-reaching, and applicable not only to other shale reservoirs but also to other subsurface operations for which DOE has major responsibilities, e.g., geologic storage of CO2, radioactive waste disposal, geothermal energy, etc. Our geomechanical modeling will provide a validated means of assessing reservoir stress perturbations associated with fracturing and fluid injection (including those related to infill wells) and also a methodology for designing the spacing for wells, stages and cluster density during hydraulic stimulation. Simulation of the time evolution of reservoir strain resulting from stimulation/injection stress perturbations will form the basis for quantitative assessment of geophysical observations, including the response of fiber optic networks and the potential for injection-related, disruptive seismicity. Understanding the fundamental transport and chemical reactions occurring upon stimulation and production in hydrocarbon-bearing lithologies will support enhanced oil recovery with CO2, methane, ethane, modifying driving potentials including osmotic potentials and how such fluids modify the properties and transport of hydrocarbons. The HFTS project provides an ideal opportunity to develop both enhanced pore-scale transport model and validate reservoir scale geomechanical and geochemical/hydrologic simulations and provide an important step forward in developing a more quantitative assessment of the impact of subsurface operations.
The proposed work is a 2-year effort which brings together advanced simulation and experimental capabilities at four national laboratories, namely LBNL, LLNL, NETL, and SLAC. Potential follow-up work is detailed at the end of this document, including the idea of comparing the new national-lab framework for microscopic to reservoir-scale simulations with industry simulators, an activity that could be focused on soon-to-be-available data sets from recently awarded shale field test sites such as the Eagle Ford Shale Laboratory (EFSL).