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Results
Abstract A process to geoengineer hydrodynamic seals is investigates numerically. It is well-documented that upon mixing, Barium- and sulfate-rich brines lead to rapid deposition of impermeable and stable scale. When deposited within open fractures, the mineral scale also holds significant tensile strength. This work investigates the intentional injection of these incompatible ions into faulted formations and around caverns to create mechanically resilient hydrodynamic seals. A coupled hydrological-mechanical-chemical HMC model is calibrated to available bench-scale experimental observations. The model attains a close match with experimental core-flooding observations by fitting reaction rate, solubility, precipitation, and nonequilibrium formation blockage. It is then applied to conduct field-scale investigations of various synthetic operational injection scenarios. The calibrated simulations suggest that the saturation index of the injected brines, injection patterns, and rates have a first-order impact on seal creation and uniformity. With inorganic precipitation, the critical injection rates to triggering seismic nucleation may be reinforced by one to two orders in magnitude due to cohesive mechanical healing.
- Reservoir Description and Dynamics > Storage Reservoir Engineering (1.00)
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery (1.00)
Abstract The reservoir simulation system of residual equations is composed by applying a single parameterized nonlinear function to each cell in a mesh. This function depends on the unknown state variables in that cell as well as on those in the neighboring cells. Anecdotally, the solution of these systems relies on both the level of nonlinearity of this single-cell function as well as on how tightly the cell equations are coupled. This work reformulates this system of equations in an equivalent that is only mildly nonlinear. In an amortized offline regression stage, the single-cell equation is solved over a sampling of possible neighboring states and parameters. A neural network is regressed to this data. An equivalent residual system is formed by replacing the single-cell residual function with the neural network, and we propose three alternative algorithms to solve these preconditioned systems. The first method applies a Picard iteration that does not require Jacobian matrix evaluations or linear solution. The second applies a modified Seidel iteration that additionally infers locality automatically. The third algorithm applies Newton's method to the preconditioned system. The solvers are applied to a one-dimensional incompressible two-phase displacement problem with capillarity and a general two-dimensional two-phase flow model. We investigate the impacts of neural network regression accuracy on the performance of all methods. Reported performance metrics include the number of residual/network evaluations, linear solution iterations, and scalability with time step size. In all cases, the proposed methods significantly improve computational performance relative to the use of standard Newton-based solution methods.
Abstract Recent technological advances to trigger high-energy seismic waves from within the wellbore have spurred interest in their application to induce fracturing. While a considerable body of recent experiments at the bench scale (on the order of 1 cubic foot) show promise, there remains considerable uncertainty in how the process scales. This work characterizes the scaling relationships between the extent and intensity of fracturing stimulation and stress-wave characteristics. Our approach leverages direct numerical simulation of the elastodynamic equations accounting for nonlinear fracture mechanics. We apply a hybrid Finite-Discrete Element Method (FDEM) where cohesive (elasto-plastic) laws hold mesh elements together until complete failure. Beyond failure, elements act as deformable free bodies that can interact via contact constraints. An infinite domain is modeled with a spherical inclusion within which an impulsive load is imposed. The dynamic load models a rise time to a peak pressure, followed by a decay period, and all occurring within micro- to milliseconds. The model is validated with experimental observations at the bench scale after mesh-refinement verification. Finally, the model is used to explore the dimensionless parameter space by varying loading characteristics (rise time, peak pressure, and impulse) to reveal the stimulated damaged bulk volume and the crack intensity within it. At the bench scale, the model reproduces a nearly linear trend between damage radius and peak stress. Beyond that, however, the model predicts that this scaling slows considerably to a fractional power law between the damaged radius and the peak stress. This limitation is coincident with a geometric increase in the intensity of damage within the stimulated volume.
Abstract We present an efficient time-continuation scheme for fluid-driven fracture propagation problems in the frame-work of the extended finite element method (XFEM). The fully coupled, fully implicit hydro-mechanical system is solved in conjunction with the linear elastic fracture propagation criterion by the Newton-Raphson method. Therefore, at the end of each time-step solve, the model ensures the energy release rate of weakest fracture tips within the equilibrium propagation regime. Besides, an initialization procedure for newly created fracture space as well as a priori estimate of stress intensity factor (SIF) growth rates are also developed to further improve the solver performance. We validate the model by the analytical solution and extend the problem to the multiple fracture propagation where stress shadow phenomenon occur.
Abstract Automatic differentiation software libraries augment arithmetic operations with their derivatives, thereby relieving the programmer of deriving, implementing, debugging, and maintaining derivative code. With this encapsulation however, the responsibility of code optimization relies more heavily on the AD system itself (as opposed to the programmer and the compiler). Moreover, given that there are multiple contexts in reservoir simulation software for which derivatives are required (e.g. property package and discrete operator evaluations), the AD infrastructure must also be adaptable. An Operator Overloading AD design is proposed and tested to provide scalability and computational efficiency seemlessly across memory- and compute-bound applications. This is achieved by 1) use of portable and standard programming language constructs (C++17 and OpenMP 4.5 standards), 2) adopting a vectorized programming interface, 3) lazy evaluation via expression templates, and 4) multiple memory alignment and layout policies. Empirical analysis is conducted on various kernels spanning various arithmetic intensity and working set sizes. Cache- aware roofline analysis results show that the performance and scalability attained are reliably ideal. In terms of floapting point operations executed per second, the performance of the AD system matches optimized hand-code. Finally, the implementation is benchmarked using the Automatically Differentiable Expression Templates Library (ADETL).
- Europe (1.00)
- North America > United States (0.28)
- Research Report > New Finding (0.48)
- Research Report > Experimental Study (0.48)
Abstract In the context of remote sensing, the vast disparity in characteristic scales between seismic deformation (e.g. milliseconds) and transient flow (e.g. hours) allows a "two-model paradigm" for geophysics and reservoir simulation. In the context of flow-induced geohazard risk mitigation and micro-seismic data integration, this paradigm breaks down. Under micro-seismic deformation, events occur with high-frequency, and over sustained duration during which the rock-fluid coupling is significant. In risk mitigation scenarios, the onset of seismic deformation is directly tied to quasi-static coupling periods. This work develops an approach to reservoir simulation modeling that allows simultaneous resolution of transient (inertial) poromechanics and multiphase fluid flow in the presence of fracture. A mixed discretization scheme combining the extended finite element method (XFEM) and the embedded discrete fracture model (EDFM) is extended using a second-order implicit Newmark time integration scheme for the inertial mechanics. A Lagrange multiplier method is developed to model pressure-dependent contact traction in fractures. The contact constraints are adapted to accommodate fracture opening. Slip-weakening fracture friction models are incorporated. Finally, a time-step controller is proposed to combine local discretization error with contact traction and slip-rate control along the fractures. This strategy allows automatic adaptation to resolve quasi-static, inter-seismic triggering, and co-seismic spontaneous rupture periods within one model. The model is verified to simulate complete induced earthquake sequences, including inter-seismic and dynamic rupture phases. The performance of the adaptive model is illustrated for cases with various set-ups of production and injection periods in a fractured reservoir with explicit fracture representation.
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Abstract Fracture propagation (FP) occurs in extensive applications including hydraulic fracturing, underground disposal of liquid waste, CO2 sequestration etc. It is crucial to develop a simulator that is able to reflect physics behind FP and capture the FP path. This work is an extension of the previous developed model (Ren et al. (2018), Ren & Younis (2018)) to the simulation of FP. One of the remarkable benefits using the coupled XFEM-EDFM scheme allows FP free of the remeshing. In this work, the onset of FP is controlled by a single parameter, the equivalent stress intensity factor (SIF). A domain integral method, J integral is applied to extract the SIF information. A time marching scheme is performed to ensure the SIF criterion satisfied everytime fracture propagates. The developed simulator is verified by the analytical solutions and shows the capability of FP simulation in poroelastic materials.
Abstract An XFEM-EDFM scheme and associated monolithic solution method are proposed to model time-dependent poromechanics and two-phase flow. Fractures are modeled as interfaces with displacement discontinuities. The contact forces are treated using Lagrange Multipliers. A number of numerical tests are performed to investigate the Newmark scheme's accuracy and cases for wave propagation in poroelastic and natural fracture media are implemented to evaluate computational efficiency. We apply the method to model seismic data from hydraulic fracture network. Empirical results validate the Newmark scheme accuracy as well as computational efficiency and localization of newton update in seismic field is necessary for the further application. The synthetic model of multiple hydraulic stages illustrates the effect of flow coupling and newly generated fractures on the microseismic field. The model is applied to simultaneously assimilate well performance and microseismic observations, thereby informing about the causal event dynamics.
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
Abstract The use of full-physics models in close-loop reservoir management can be computationally prohibitive as a large number of simulation runs are required for history matching and optimization. In this paper we propose the use of a physics-based data-driven model to accelerate reservoir management and we describe how it could be implemented with a commercial simulator. In the proposed model, the reservoir is modeled as a network of 1D flow paths connecting perforations at different wells. These flow paths are discretized and the properties at each grid block along each flow path are derived from history matching of production data. To simulate flow in this network model through a commercial simulator with all the physics, an equivalent 2D Cartesian model is set up in which each row corresponds to one of the 1D flow paths. Finally, the history matching is performed with ensemble smoother with multiple data assimilation (ESMDA). The proposed network model is tested on both waterflood and steamflood problems. It is demonstrated that the proposed model matches with well-level production history (including pressure and phase flow rate) well. The calibrated ensemble from ESMDA also provided a satisfactory probabilistic forecast of future production that almost always envelops the true solutions. This indicates that the proposed model, after calibrated with production data, is accurate enough for production forecast and optimization. In addition, the use of commercial simulator in the network model provided flexibility to account for complex physics, as demonstrated by the successfully application to the steamflood problem. Compared with traditional workflow that goes through the full cycle of geological modelling, history matching and probabilistic forecasting, the proposed network model only requires production data and can be built within hours. The resulted network model also runs much faster than a full-physics as it typically has much less grid blocks. We expect the proposed method to be most useful for mature fields when abundant of production data is available. As far as we know, this is first time a physics-based data-driven model is implemented with a commercial simulator. The use of commercial simulator makes it easy to extend the model for complex reservoir such as thermal or compositional reservoirs.
Abstract A mixed discretization approach is propsed to adequately resolve fracture system while accurately and efficiently modeling both flow and geomechanics. An extended finite element method (XFEM) is applied to approximate the geomechanics, and an embedded-discrete-fracture model (EDFM) is used to model the multiphase flow equations. The two schemes are fully coupled, and the time discretization for flow is fully-implicit. Moreover, a hybrid fracture representation concept is employed where the dual porosity approach is used in conjunction with the embedded discrete representation in order to capture small-scale fracture networks efficiently.