Fracture Flow
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Prashant Unnikrishnan Nair

In real-world water injection applications, an in-line injection facilitates a pressure differential that boosts the current flow. A pressure differential created by the injection of a pressurized flow into the mainline of flow is derived from the momentum transfer equation. Heat loss is disregarded, and such empirical equations provide a ballpark value to these pressure differentials during the injection. In industrial applications, injection of the fluid is done on the surface, due to weld and other constraints where losses due to friction and eddy current formation are imminent. On the other hand, penetration injection provides a far more augmented pressure differential that has a polynomial impact based on the mainline flow rate and the injection flow rate. This paper aims to derive an accurate representation of the pressure differential values obtained from a penetration injection through experimentation and compare it against a surface injection or empirical calculation. The paper concludes by indicating that the penetration injection augments the pressure differential with a new empirical formula for the derived pressure differential as a polynomial equation for this apparatus and can be extended across different sizes of the mainline and injection line diameters. This work provides a precise formula that can be used to derive pressure differential and estimate the flow and pressure rates. The formula also provides a platform for further utility in the fracturing operations where fracture flow from the well upstream presents multiple injection fractures to the mainline through fracture pores.

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Zhiyu Liu ◽  
Fan Fan ◽  
Donghang Zhang ◽  
Yang Li ◽  
Yuan Li ◽  

Slick-water can effectively reduce the flow drag of fracturing fluid. Many studies have focused on the drag reduction performance of slick-water in wellbore and perforation, but there has been little research on drag reduction characteristics in fracture flow. In this paper, a new visualization experiment system is used to simulate real fracture. The fracture surface is produced through actual triaxial hydraulic fracturing and is copied by a three-dimensional printer using resin material to maintain its shape feature. In comparing the experimental results, it was found that the main factors affecting drag reduction in a fracture are the relative molecular weight and the added concentration. Unlike the flow rule of the drag reducer in a pipeline, when the concentration is greater than 0.10%, a negative DR effect begins to appear. The influence of molecular weight is related to the flow stage; the increasing of molecular weight causes a reduction in DR effect when the flow rate is 0.24 m/s. However, the flow rate exceeds 0.5 m/s; drag reducers with higher molecular weight demonstrate better drag reduction performance. The drag reduction mechanism analysis in fractures was obtained from visualization observations, and the flow characteristics of fluid were characterized by using tracking particles. Drag reduction effect occurs mainly on the surface of the fractures in contrast to near the centre of the flow channel. This research can provide a reference for the experimental study on drag reduction in fractures and is of great significance to the optimization and improvement of drag reducing agent.

2021 ◽  
Vol 11 (19) ◽  
pp. 9148
Luat Khoa Tran ◽  
Stephan Konrad Matthai

We study infiltration of rainwater into fractured rock and the accompanying capillary exchange processes between fractures and matrix, hereafter referred to as fracture–matrix transfer (FMT). Its influence on the velocity of the wetting front for uniform and variable aperture fractures is of prime interest because it determines the penetration depth of infiltration pulses. FMT is modelled explicitly in a discrete fracture and matrix (DFM) framework realised using a hybrid finite element–finite volume discretisation with internal boundaries. The latter separate the fracture mesh from the rock matrix mesh with the benefit that the flow that occurs within the minute fracture subvolume can be tracked with great accuracy. A local interface solver deals with the transient nonlinear aspects of FMT, including spontaneous imbibition of the rock matrix. Two- and three-dimensional heuristic test cases are used to illustrate how FMT affects infiltration. For the investigated scenario, we find that—beyond a critical fracture aperture around 5–10-mm—infiltration rate is no longer affected by FMT. Fracture aperture variations promote in-fracture-plane fingering, with counter-current flow of water (downward) and air (upward). Fracture flow interacts with FMT in a complex fashion. For systems with a small fracture porosity (≤0.01%), our results suggest that intense, hour-long rainfall events can give rise to tens-of-meter-deep infiltration, depending on fracture/matrix properties and initial saturation of the fractured rock mass.

2021 ◽  
Vol 927 ◽  
Yue Gao ◽  
Emmanuel Detournay

A two-dimensional model of a hydraulic fracture propagating in a weakly consolidated, highly permeable reservoir rock during a waterflooding operation is described in this paper. The model recognizes the essential differences that exist between this class of fractures and conventional hydraulic fracturing treatments of oil and gas wells, namely: (i) the large-scale perturbations of pore pressure and the associated poroelastic effects caused by extended injection time; (ii) the extremely small volume of fluid stored in the fracture compared with the injected volume; and (iii) the leakage of water from both the borehole and the propagating fracture. The model consists of a set of equations encompassing linear elastic fracture mechanics, porous media flow and lubrication theory. Three asymptotic solutions applicable at different time regimes are found theoretically, and numerical results are obtained from the discretized governing equations. The solution reveals that the injection pressure does not evolve monotonically, as it increases with time in the early time radial-flow regime but decreases in the late time fracture-flow regime. Thus, the peak injection pressure does not correspond to a breakdown of the formation, as usually assumed, but rather to a transition between two regimes of porous media flow. However, this problem exhibits an extreme sensitivity of the time scales on a dimensionless injection rate $\mathcal {I}$ . If $\mathcal {I} \lessapprox 1$ , the time to reach the peak pressure could become so large that it cannot be observed in field operations, i.e. the fracture remains hydraulically invisible. Finally, it is found that poroelasticity significantly affects the response of the system, by increasing the injection pressure and delaying the time at which the peak pressure takes place.

Ivar Stefansson ◽  
Eirik Keilegavlen ◽  
Sæunn Halldórsdóttir ◽  
Inga Berre

AbstractConvection-driven cooling in porous media influences thermo-poro-mechanical stresses, thereby causing deformation. These processes are strongly influenced by the presence of fractures, which dominate flow and heat transfer. At the same time, the fractures deform and propagate in response to changes in the stress state. Mathematically, the model governing the physics is tightly coupled and must account for the strong discontinuities introduced by the fractures. Over the last decade, and motivated by a number of porous media applications, research into such coupled models has advanced modelling of processes in porous media substantially. Building on this effort, this work presents a novel model that couples fracture flow and heat transfer and deformation and propagation of fractures with flow, heat transfer and thermo-poroelasticity in the matrix. The model is based on explicit representation of fractures in the porous medium and discretised using multi-point finite volume methods. Frictional contact and non-penetration conditions for the fractures are handled through active set methods, while a propagation criterion based on stress intensity factors governs fracture extension. Considering both forced and natural convection processes, numerical results show the intricate nature of thermo-poromechanical fracture deformation and propagation.

2021 ◽  
Vol 2011 (1) ◽  
pp. 012014
Yetong Xie ◽  
Jing Li ◽  
Ziyi Song ◽  
Chongzhi Wang ◽  
Kaiyu Wang ◽  

2021 ◽  
R. Bharadwaj

Hydrofracking transfigured the concept of producing from unconventional reservoirs. The Fracking fluid used in fracturing has unlocked many tight reservoirs but in terms of an aquifer, it poses threats like consumption of large quantity of water and also, used water becomes polluted as well as recycling cost is uneconomic. This paper evaluates alternatives to water-based frac fluids and discusses their environmental & economic impact along with resource availability and commercial feasibility. Pure Propane Fracturing uses propane in combination with non-toxic man-made proppants (light glass & carbon fullerene microbeads) with desired properties. Pure Propane is fluorinated and carbonated without water or harmful additives, thereby eliminates the risk of catching fire. Pure Propane Fracturing eliminates the need for water completely and thus, a perfect option for fracturing in water scarcity regions. Fracture flow capacity of Pure Propane can be enhanced with the use of phase change chemical proppants in the slurry stage. CO2 Foam Fracturing predominantly comprises liquid carbon-dioxide which reduces the water requirement up to 80%. CO2 foam-based frac fluid uses relatively fewer chemical additives as compared to the water-based frac fluid which in-turn does minimal formation damage. Foam Fracturing fluids have high fluid recovery and clean-up efficiency. CO2 foam-based frac fluid is available in a wide range of viscosities and can also work in high pressure high temperature conditions at significantly low polymer loadings. Energized frac fluid comprises N2/CO2 (20-30%) which reduces water consumption and provides additional energy to aid in load recovery during the post-frac flow-back stage. N2 gas can propagate more easily into small pores and micro-fractures to get lower breakdown pressure and enhance fracture complexity & CO2 exists in dense phase at static bottom hole conditions, thus is less susceptible to dissipation and dissolves in crude oil which reduces its viscosity and improves cleanup and recovery.

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