When producing hydrocarbons from an oil well, managing erosion of both surface and subsurface components caused by solids in the flow stream is critical to maintaining operations integrity in both land and offshore assets. Although component lifetime prediction has advanced in the past few decades, the prediction's accuracy remains a major oil and gas industry challenge. Current computational models only provide an initial erosion rate which is usually assumed constant until equipment failure. However, observed erosional rates vary as a function of time due to the geometrical changes caused by equipment material loss, which result in variations in solid particle impingement velocity [
This paper presents an implementation of an erosion dynamics model in ANSYS FLUENT, a commercial computational fluid dynamics (CFD) software, to capture the progression of transient erosion. The model has the capability to capture the effects of surfaces receding from erosion at each time interval. By dynamically adjusting these surfaces and recalculating the local flow conditions in the area, this method can predict new erosion rates for each time interval and achieve fully coupled geometry-flow-erosion interactions.
This new erosion dynamics model was validated against experimental data from both literature and physical testing, and was determined to have accurately captured the observed erosion trends over time in terms of location and magnitude. The model was then employed to study two real world applications: 1) in evaluating the erosion risk for a high-rate water injector, it predicted the evolution of damage to a coupler designed to connect different diameter pipes, and 2) in analyzing facility piping systems connected to an unconventional well, it predicted the transient erosion trend from proppant flowback, which allowed for pipe geometry optimization to increase in erosional life expectancy.
This paper presents a brief review of misconceptions on industry-standard brittleness/ductility definitions; geomechanical aspects and numerical evaluation of pulse fracturing by use of an advanced constitutive model implemented within the ANSYS® Autodyn® (ANSYS 2014); and fracture-network patterns because of pulse loading in shale that show ductile/brittle transition.
In shale gas, one of the primary goals is to create extensive fracture networks that can remain open during production. Field experience has shown that not all shale formations respond to hydraulic fracturing effectively. It is important to identify and accurately design alternative fracturing techniques that would overcome some of the limitations. Pulse-fracturing rates and peak loads can be customized to lie between hydraulic and explosive fracturing. This technique has the potential to shatter shale, in particular by triggering a ductile/brittle transition at an optimized pulse rate.
To date, operational considerations of pulse fracturing for success remain qualitative. Recent advances in computational geomechanics help us quantify the effect of key operational parameters for field applications. Further to this, advanced constitutive models implemented for these analyses have the benefit of simulating ductile/brittle transition, if the stress state and loading conditions dictate that the material should. This study on pulse fracturing shows that for a certain combination of reservoir, geomechanical, and pulse-loading parameters, induced fractures can propagate in multiple directions. This phenomenon might promote a self-propping mechanism for a network of fractures. At the end of this paper, favorable conditions when the pulse-fracturing technique would work and key parameters that trigger ductile/brittle transition are summarized and presented.
This paper is a continuation of previous paper (OMAE2014-23225) where a parametric study was performed for wave- structure interaction on a hollow cylinder in regular sea waves without vessel motions, and the effect of waves and current on the motion of the cylinder and the associated forces using a high fidelity methodology (OMAE2013-11569) to couple CFD with diffraction analysis. This approach was demonstrated for predicting the motions and loads of subsea equipment and structures during offshore operations. Instead of relying on simplified equations or empirical formulations to calculate and estimate the hydrodynamics coefficients, or using steady-state CFD simulation on a stationary equipment and structure to predict drag and added masses on submerged structures in traditional approaches, this methodology couples the transient CFD with diffraction analysis. In this paper, we extend the solution to include wave-structure interaction in irregular sea waves and vessel motions. Irregular waves are modelled using a JONSWAP wave spectrum. Simulations are performed to investigate effect of significant wave height, peak wave frequency (time period) of irregular sea waves, and vessel motions on the motion of a hollow cylinder in irregular sea waves. The results are compared with the traditional approach in current practice.
The time domain diffraction simulation is coupled with multiphase CFD simulation of subsea equipment and structures in waves. A transient CFD model with rigid body motion for the equipment and structure calculates added masses, forces and moments on the equipment and structure for diffraction analysis, while diffraction analysis calculates linear and angular velocities for CFD simulation.
The results provide better understanding of structure motion and associated forces in waves using this coupled methodology. The coupled methodology eliminates the inaccuracy inherited from assumed or calculated hydrodynamic properties that are obtained by using simplified equations or empirical formulations, or by using steady - state CFD analyses in traditional decoupled approaches. This coupled methodology has potential applications in analyses of the motions of subsea equipment and structures in waves during offshore operations.
Ability to induce complex, highly connected fracture networks, that can remain open during production, is the key to unlock permeability challenged shale gas plays. Within the time and pressure scale of hydraulic fracturing operations, it is difficult to create fracture complexity in ductile shales. However, when subjected to a high rate/pulse loading, rock might exhibit a brittle to ductile transition and a complex fracture network might be created. Along these lines, the concept of pulsed fracturing, that customizes the pressure-time behavior of a pulse source to create multiple fractures, is introduced. In this paper, an integrated 3D model that quantifies fracture initiation, growth, and coalescence due to initial and post-peak pulse loading is presented. The simulation involves a numerical algorithm that couples tensile/shear/compactive failure algorithms with dynamic fracture propagation and pore fluid pressure. Geomechanical modeling approach makes it possible to optimize pulsed fracturing for different shale plays. After constitutive model description and presentation of key aspects of the model, the model is employed to a reservoir dataset to evaluate pulsed fracturing as an alternative fracturing technique. The results show that, if designed accurately, pulsed fracturing could help trigger a ductile to brittle transition and can generate complex fracture networks.
Successful installation of subsea structures and equipment is critical for offshore campaigns in development of deep-water fields. This paper presents a novel approach using Fluid-Structure Interaction (FSI) to predict wave induced motions, wave loads, dynamic stresses and deformation of subsea structure and equipment in the splash zone during installation. This approach combines transient multiphase CFD simulation including dynamic mesh motion with transient nonlinear Computational Structural Dynamics including tension forces in non-linear flexible slings. This proposed approach has been successfully implemented for lowering of a subsea manifold in splash zone during installation.
This paper has many potential applications, such as, installation of manifold, subsea tree, PLET/PLEM, suction pile, pump station, or other subsea structure and equipment.
In this coupled FSI approach, pressure loads on the structure due to wave slamming from CFD model is mapped to FEA model of structure-sling assembly, which provides motion and deformation to CFD model. The results clearly show the advantage of this FSI approach to capture the coupled physics of wave slamming and its interaction with the structure and subsequent motions of structure which is being lowered in the splash zone that other approaches cannot capture. Structural integrity of the subsea structure and equipment as well as the sling forces is well evaluated and predicted with this approach.
Traditional approaches for prediction of the motions and loads of subsea structure/equipment during installation rely on simplified formulations or empirical equations or model test to determine the wave loads on structures. It cannot simulate wave-structure interaction, nor the dynamic stress and deformation of structure/equipment due to wave-structure interaction.
The approach proposed in this paper provides a state-of-the-art FSI tool which enhances understanding wave-structure interaction in splash zone during installation. The dynamic stress obtained by using this approach can be used for quantifying fatigue damage of every component on the structure/equipment due to wave loads in splash zone during installation.
This paper presents: (i) a brief review of misconceptions on industry standard brittleness/ductility definitions, (ii) geomechanical aspects & numerical evaluation of pulsed fracturing using an advanced constitutive model implemented within the AUTODYN code, and (iii) fracture network patterns due to pulsed loading in shale that show ductile-brittle transition.
In shale gas, one of the primary goals is to create extensive fracture networks that can remain open during production. Field experience has shown that not all shale formations respond to hydraulic fracturing effectively. It is important to identify and accurately design alternative fracturing techniques that would overcome some of the limitations. In general, hydraulic fracturing involves a relatively slow rate of loading on surrounding rock and results in bi-wing fracture geometries. Explosive fracturing involves very rapid loading of the formation and results in simultaneous propagation of multiple fractures. However, due to extreme stress/heat generated during the explosion, near wellbore region might reach plastic flow and/or compaction limit. Pulsed fracturing rates and peak loads (via high energy gas or propellants) can be customized to lie between hydraulic and explosive fracturing. This technique has the potential to shatter shale, in particular by triggering a ductile to brittle transition at an optimized pulse rate. That is, brittleness or fracture potential is not a "material property?? but rather a "material behavior?? that can be modified.
Pulsed fracturing is characterized in the field by peak pressures exceeding both the maximum and minimum in-situ stresses. However, operational considerations for success remain qualitative. Recent advances in computational geomechanics help us quantify the effect of key parameters on pulsed fracturing techniques for field applications. Further to this, advanced constitutive models implemented for these analyses have the benefit of simulating ductile to brittle transition, if the stress state & loading conditions dictate that the material should. This study on pulsed fracturing shows that for a certain combination of reservoir, geomechanical and pulse loading parameters: fractures can propagate in multiple directions. This phenomenon might promote a self-propping mechanism for a network of fractures. At the end, favorable conditions when pulsed fracturing technique would work and key parameters that trigger ductile to brittle transition are summarized and presented.