Digital Slot: A Tool for Optimization and Development of New Hydraulic Fracturing Technologies

We present the digital slot — a tool for the development of new hydraulic fracturing technologies via digitization of slurry flow in narrow channels. We consider slurry containing fluid, proppant, and fiber components. The flow is described by a continuum mathematical model based on the lubrication theory. The numerical algorithm utilizes Lagrangian approach with finite volume pressure solver. We present the results of laboratory validation and simulation examples showing the key effects affecting solids transport in hydraulic fracturing: settling, bridging, gravity slumping, materials degradation, viscosity contrast, and bank formation.

Delivering Automated Reservoir Management with Birth of the First Ever Universal Inflow Control System UICS

Conventional ICDs were invented for long horizontal wells to promote a more uniform inflow profile. Later, AICDs were developed, which utilize viscosity contrast between fluids to impose a larger hydraulic resistance in sections with inflow of undesired fluids, like gas and water. However, these AICD technologies cannot be used to choke back inflow of water in reservoirs where oil and water have similar viscosities, and they also tend to impose large pressure drops even for single-phase oil at high flow rates. The objective of the work presented here has therefore been to develop an inflow control technology that removes these limitations. The resulting Density Activated Recovery (DAR™) technology utilizes difference in fluid density rather than viscosity contrast to control fluids downhole. It is a fully autonomous, binary system that is either fully open or closed, where "closed" means that it only allows a small pilot flow. More specifically, it can be considered a "dual ICD" with flow through a large port when open, and a small port when "closed". The flow capacity and choking efficiency are therefore fully defined by the diameters of these two ports. Furthermore, it can close and reopen at any pre-determined water and gas fractions, that are completely insensitive to flow rate, viscosity and Reynolds number. This makes it universally applicable to control any wellbore fluid along the entire reservoir section. After successful prototype testing in 2018, the DAR technology has now undergone a comprehensive full-scale system-qualification program including a final flow performance test where the system was tested at 240 bar and 90ºC with saturated 0.8 cP oil. The tests demonstrated up to seven times higher flow capacity with the density-based DAR technology compared with viscosity-dependent AICD technologies. The system successfully and repeatedly closed and reopened for both gas and water. As oil and water had similar viscosities, the tests also proved how this technology can be used to stop undesired inflow of water in light-oil reservoirs. Being insensitive to flow rate, the DAR system is also insensitive to local variations in pressure and productivity along the reservoir section, which reduces the negative consequences of geological uncertainty and allows the same design to be used at every location in the well. It can also be configured to ensure complete mud removal during well cleanup and can even stop inflow of water in gas wells, where the undesired fluid has higher viscosity than the desired fluid. More importantly, this technology can deliver automated reservoir management to a level where it influences how wells are drilled and fields are developed. Accelerated oil production and the reduced need for reinjection of gas/water will also reduce the associated greenhouse gas (GHG) emissions considerably.

Viscous banding instabilities: non-porous viscous fingering

We demonstrate a novel instability found within unconfined viscous bands/rims, or free-surface flows involving a longitudinal viscosity contrast. Such instabilities may be described as viscous banding instabilities, non-porous viscous fingering instabilities or unconfined viscous fingering instabilities of free-surface flows involving the intrusion of a less viscous fluid into a band of more viscous fluid. A consequence of this work is that viscous fingering instabilities, widely known to occur in porous media following the seminal work of Saffman & Taylor (Proc. R. Soc. Lond. A, vol. 245, 1958, pp. 312–329), also occur in non-porous environments. Although the mechanism of the viscous banding instability is characteristically different from that of the Saffman–Taylor instability, there are important similarities between the two. The main similarity is that a viscosity contrast leads to instability. A distinguishing feature is that confinement, such as the rigid walls of a Hele-Shaw cell, is not necessary for viscous banding instabilities to occur. More precisely, Saffman–Taylor instabilities are driven by a jump in dynamic pressure gradient, whereas viscous banding instabilities, or non-porous viscous fingering instabilities, are driven by a jump in hydrostatic pressure gradient, directly related to a slope discontinuity across the intrusion front. We examine the onset of instability within viscous bands down an inclined plane, determine conditions under which viscous banding instabilities occur and map out a range of behaviours in parameter space in terms of two dimensionless parameters: the viscosity ratio and the volume of fluid ahead of the intrusion front.

Modeling Red Blood Cell Viscosity Contrast Using Inner Soft Particle Suspension

The inner viscosity of a biological red blood cell is about five times larger than the viscosity of the blood plasma. In this work, we use dissipative particles to enable the proper viscosity contrast in a mesh-based red blood cell model. Each soft particle represents a coarse-grained virtual cluster of hemoglobin proteins contained in the cytosol of the red blood cell. The particle interactions are governed by conservative and dissipative forces. The conservative forces have purely repulsive character, whereas the dissipative forces depend on the relative velocity between the particles. We design two computational experiments that mimic the classical viscometers. With these experiments we study the effects of particle suspension parameters on the inner cell viscosity and provide parameter sets that result in the correct viscosity contrast. The results are validated with both static and dynamic biological experiment, showing an improvement in the accuracy of the original model without major increase in computational complexity.

Importance of Viscosity Contrast for the Motion of Erythrocytes in Microcapillaries

The dynamics and deformation of red blood cells (RBCs) in microcirculation affect the flow resistance and transport properties of whole blood. One of the key properties that can alter RBC dynamics in flow is the contrast λ (or ratio) of viscosities between RBC cytosol and blood plasma. Here, we study the dependence of RBC shape and dynamics on the viscosity contrast in tube flow, using mesoscopic hydrodynamics simulations. State diagrams of different RBC dynamical states, including tumbling cells, parachutes, and tank-treading slippers, are constructed for various viscosity contrasts and wide ranges of flow rates and tube diameters (or RBC confinements). Despite similarities in the classification of RBC behavior for different viscosity contrasts, there are notable differences in the corresponding state diagrams. In particular, the region of parachutes is significantly larger for λ = 1 in comparison to λ = 5. Furthermore, the viscosity contrast strongly affects the tumbling-to-slipper transition, thus modifying the regions of occurrence of these states as a function of flow rate and RBC confinement. Also, an increase in cytosol viscosity leads to a reduction in membrane tension induced by flow stresses. Physical mechanisms that determine these differences in RBC dynamical states as a function of λ are discussed.

Effects of heterogeneity on frictional-viscous deformation and the depth-extent of the seismogenic zone

<p>Current conceptual fault models define a seismogenic zone, where earthquakes nucleate, characterised by velocity-weakening fault rocks in a dominantly frictional regime. The base of the seismogenic zone is commonly inferred to coincide with a thermally controlled onset of velocity-strengthening slip or distributed viscous deformation. The top of the seismogenic zone may be determined by low-temperature diagenetic processes and the state of consolidation and alteration. Overall, the seismogenic zone is therefore described as bounded by transitions in frictional and rheological properties. These properties are relatively well-determined for monomineralic systems and simple, planar geometries; but, many exceptions, including deep earthquakes, slow slip, and shallow creep, imply processes involving compositional, structural, or environmental heterogeneities. We explore how such heterogeneities may alter the extent of the seismogenic zone.</p><p> </p><p>We consider mixed viscous-frictional deformation and suggest a simple rule of thumb to estimate the role of heterogeneities by a combination of the viscosity contrast within the fault, and the ratio between the bulk shear stress and the yield strength of the strongest fault zone component. In this model, slip behaviour can change dynamically in response to stress and strength variations with depth and time. We quantify the model numerically, and illustrate the idea with a few field-based examples: 1) earthquakes within the viscous regime, deeper than the thermally-controlled seismogenic zone, can be triggered by an increase in the ratio of shear stress to yield strength, either by increased fluid pressure or increased local stress; 2) there is commonly a depth range of transitional behaviour at the base of the seismogenic zone – the thickness of this zone increases markedly with increased viscosity contrast within the fault zone; and 3) fault zone weakening by phyllosilicate growth and foliation development increases viscosity ratio and decreases bulk shear stress, leading to efficient, stable, fault zone creep. These examples are not new interpretations or observations, but given the substantial complexity of heterogeneous fault zones, we suggest that a simplified, conceptual model based on basic strength and stress parameters is useful in describing and assessing the effect of heterogeneities on fault slip behaviour.         </p>

Importance of viscosity contrast for the motion of erythrocytes in microcapillaries

ABSTRACTThe dynamics and deformation of red blood cells (RBCs) in microcirculation affect the flow resistance and transport properties of whole blood. One of the key properties that can alter RBC dynamics in flow is the contrast λ (or ratio) of viscosities between RBC cytosol and blood plasma. Here, we study the dependence of RBC shape and dynamics on the viscosity contrast in tube flow, using mesoscopic hydrodynamics simulations. State diagrams of different RBC dynamical states, including tumbling cells, parachutes, and tank-treading slippers, are constructed for various viscosity contrasts and wide ranges of flow rates and tube diameters (or RBC confinements). Despite similarities in the classification of RBC behavior for different viscosity contrasts, there are notable differences in the corresponding state diagrams. In particular, the region of parachutes is significantly larger for λ = 1 in comparison to λ = 5. Furthermore, the viscosity contrast strongly affects the tumbling-to-slipper transition, thus modifying the regions of occurrence of these states as a function of flow rate and RBC confinement. Also, an increase in cytosol viscosity leads to a reduction in membrane tension induced by flow stresses. Physical mechanisms that determine these differences in RBC dynamical states as a function of λ are discussed.