Showing papers on "Annulus (oil well) published in 2018"

Direct numerical simulation of a turbulent core-annular flow with water-lubricated high viscosity oil in a vertical pipe

Abstract: The characteristics of a turbulent core-annular flow with water-lubricated high viscosity oil in a vertical pipe are investigated using direct numerical simulation, in conjunction with a level-set method to track the phase interface between oil and water. At a given mean wall friction ( , where is the friction velocity, is the pipe radius and is the kinematic viscosity of water), the total volume flow rate of a core-annular flow is similar to that of a turbulent single-phase pipe flow of water, indicating that water lubrication is an effective tool to transport high viscosity oil in a pipe. The high viscosity oil flow in the core region is almost a plug flow due to its high viscosity, and the water flow in the annular region is turbulent except for the case of large oil volume fraction (e.g. 0.91 in the present study). With decreasing oil volume fraction, the mean velocity profile in the annulus becomes more like that of turbulent pipe flow, but the streamwise evolution of vortical structures is obstructed by the phase interface wave. In a reference frame moving with the core velocity, water is observed to be trapped inside the wave valley in the annulus, and only a small amount of water runs through the wave crest. The phase interface of the core-annular flow consists of different streamwise and azimuthal wavenumber components for different oil holdups. The azimuthal wavenumber spectra of the phase interface amplitude have largest power at the smallest wavenumber whose corresponding wavelength is the pipe circumference, while the streamwise wavenumber having the largest power decreases with decreasing oil volume fraction. The overall convection velocity of the phase interface is slightly lower than the core velocity. Finally, we suggest a predictive oil holdup model by defining the displacement thickness in the annulus and considering the boundary layer characteristics of water flow. This model predicts the variation of the oil holdup with the superficial velocity ratio very well.

Parameters Affecting Efficient Solid Circulation Rate in Draft Tube Spouted Bed

Abstract: Solid circulation rate in a draft tube spouted bed is an important parameter for its industrial use. It can be manipulated adjusting the dimensions of the draft tube and entrainment height above the gas inlet nozzle and is studied here for a wide range of spouting gas velocities. A maximum entrainment height is identified and seen to show strong correspondence with the ratio between the projected volumes of annulus and spout zones below the draft tube. Overall energy loss at the spout-annulus interface has been reported for the first time as a function of particle size. Solid circulation rate is seen to be highly affected by flow resistance due to the passage of solid flow between conical apparatus wall and the draft tube and solid pressure in the annulus and can be well varied by changing the spouting gas velocity and fixing at a critical value.

Transient pressure driven flow in an annulus partially filled with porous material: Azimuthal pressure gradient

Abstract: Received: 23 June 2018 Accepted: 4 September 2018 The transient flow formation due to sudden application of constant circumferential pressure gradient in an annulus partially filled with porous material has been considered. An exact solution of the governing equations has been obtained in Laplace domain using Laplace transform technique. Using suitable transformations, the equations are converted into standard Bessel equations whose solutions are available in the literature. The solutions to the Bessel equations are then inverted to the time domain using Riemann-sum approximation approach. The implicit finite difference scheme has also been employed in solving the governing equations in other to establish the accuracy of the Riemann-sum approximation approach for both transient and steady state solutions. The obtained solutions are then analysed for various dimensionless parameters entering the unified problem. There is a clear indication that large value of Da enhances the permeability of the porous region. Also, thin clear fluid region boosts τ1 but has no significant influence on τλ. While thin porous region enhances skin friction at both surfaces.

A model on dual string drilling: on the road to deep waters

Abstract: As the offshore market is facing the deepwater production challenges, the Oil and Gas Industry is investing in new technologies to bring down costs needed to effectively exploit reservoirs. Therefore, dual string drilling (DSD) can eliminate the marine riser which would result in exploring oil fields in deep and ultra-deepwater economically. In order for controlling fluid contact with a borehole wall during drilling operations include introducing an outer pipe into a borehole and positioning an inner pipe within the outer pipe axially. The method may further include circulating a drilling fluid to a drill bit using inner pipe and the annulus between the inner pipe and outer pipe. The drilling fluid may be separated from the control fluid by using an annular isolator. The results showed that with DSD approach a lot of time will be saved in order to circulate the kick out of the well. Apart from riserless drilling, DSD has an efficient cutting removal capacity, better annular clearance, elimination of differential sticking, better well stability, better well control parameters, reduction of torque and drag, avoid the dynamic equivalent circulating density gradient, and better extended reach drilling. The novelty of the new dynamics model is in the ability to solve narrow operational margin between pore pressure and fracture pressure as we move into deeper waters.

Steady-State Cuttings Transport Simulation in Horizontal Borehole Annulus

Abstract: The paper presents the results of modeling the steady-state flow of drilling fluid with cuttings in an annulus for the flow regimes typical for horizontal drilling. The studied parameters include effects like fluid rheology, drillstring rotation and eccentricity on flow regime, pressure drop and cuttings bed. It has been demonstrated that increasing the drilling fluid’s effective viscosity increases the pressure drop, but it decreases the cuttings bed area, while drillstring rotation significantly changes the flow structure, improving cuttings transport and reducing the pressure drop. The considered flow structure can change abruptly due to changed drill string positioning and rheological fluid properties. Such structural changes are followed by abrupt changes in the pressure drop and cuttings bed area.

Effect of Buoyancy and Inertia on Viscoplastic Fluid: Fluid Displacement in an Inclined Eccentric Annulus With an Irregular Section

Abstract: Primary cementing is an important well construction process that should establish well control barriers and zonal isolation. Critical for primary cementing is the successful displacement of drilling fluid from the annulus between casing and formation by a sequence of spacer fluids and cement slurry. Failure to displace the drilling fluid may compromise the annular cement integrity and result in contaminated cement with degraded mechanical properties. Issues such as eccentricity, washouts and other geometric irregularities in the wellbore can complicate the displacement processes, and their effect on the quality of the cementing job and the final result is linked to uncertainty. We present numerical simulations of the displacement process between two viscoplastic fluids in the vicinity of a symmetric local hole enlargement. The study is limited to laminar flow regimes in the regular part of the annulus, and we focus on a near-horizontal section with significant eccentricity and small annular clearance. We vary the volumetric flow rate and the mass density difference between the fluids, and study how the irregularity affects the displacement efficiency and the presence of residual fluid in and after the irregularity. In the regular part of the geometry, eccentricity favors flow in the wider, upper part of the annulus, while density difference leads to azimuthal flow from the top to the low side of the annulus. The results support the assumption that increasing the mass density difference improves the displacement efficiency. In the laminar regime, lower flow rates can be favorable over higher ones in terms of efficiency measured as a function of volume that is pumped into the enlarged section. Displacement of drilling fluids for primary cementing is a rich flow problem involving different non-Newtonian fluids and possibly irregular geometry. Simulations of the displacement process can aid in optimizing fluid properties and injection rates for primary cementing operations, and assist cement log interpretation after the operation.

Prediction of sealed annular pressure between dual packers in HPHT deepwater wells

Abstract: High-pressure and high-temperature (HPHT) deepwater oil and gas wells are under the influence of high-temperature formation fluid after putting into production. The thermal expansion pressure of sealed annular fluids caused by the annulus temperature change has large effect on the safety of strings among dual packers. This study presented a casing-cement sheath-formation model which take into account the effect of the sealed annulus temperature and volume changes between dual packers, established a displacement function of the sealed annular fluid, the free tubing and the cemented casing that based on the thermo-elastic mechanics, analysed the influence factors of sealed annular pressure, including the expansion coefficient and elasticity modulus of annular fluid, the wall thickness of casing and tubing stings. An example of a HPHT deepwater gas well was analysed. The results show that the sealed annular pressure has a positive linear correlation with the annulus temperature difference, and annular pressure buildup with the increase of thermal expansion coefficient and elasticity modulus of the annulus fluid, decreases with the casing wall thickness. To prevent the potential risk associated with annular pressure, high-compressibility and thermal-insulated materials could be developed to control sealed annulus thermal expansion pressure.

Effectiveness of magnetic field on the flow of Jeffrey fluid in an annulus with rotating concentric cylinders

Abstract: In the present article, the flow of an incompressible Jeffrey fluid in the annulus of rotating concentric cylinders in the presence of magnetic field has been investigated. The governing equations for Jeffrey fluid model are formulated considering cylindrical coordinates system. The constitutive equations for the fluid flow have been simplified under the choice of velocity. The existence of the solution to the momentum equation is established using Schauder’s fixed point theorem. The analytical solutions for the velocity and skin friction coefficient are presented using modified Bessel functions. The effect of various parameters of interest such as the rotating speed of the cylinders, magnetic field parameter, non-Newtonian fluid parameter and the aspect ratio of cylinders on the velocity field and skin friction coefficient have been studied. It is observed that, the velocity decreases with increase in magnetic field parameter and aspect ratio of the cylinders. It is also depicted that, the higher velocities are seen in Newtonian fluid model as compared to the Jeffrey fluid model. The results obtained for the flow characteristics reveal many interesting behaviors that warrant further study of the effects of rotation on the flow characteristics.