Showing papers on "Annulus (oil well) published in 2019"

Heat transfer augmentation in double pipe water to air counter flow heat exchanger with helical surface disc turbulators

Abstract: Present investigation reports the effect of helical surface disc turbulators (HSDTs) on heat transfer and pressure drop characteristics in double pipe heat exchanger (DPHE). HSDTs has been utilized in the annulus region. Tests are conducted by insertion of HSDTs with various operating parameters including three different diameter ratios (DR = do/Di = 0.42, 0.475 and 0.54), three different helix angles (ɸ = 20°, 30° and 40°) and varied range of Reynolds Number (3500–10500). Water, used as hot fluid, flows in the inner tube, while air, used as cold fluid, flows through the annulus. The tests are conducted for air for uniform wall temperature condition. The heat exchanger with least diameter ratio and increased helix angle is found to exhibit the highest Nusselt number and friction factor. Results indicate that maximum enhancement is obtained for smallest diameter ratio (DR = 0.42) and helix angle (ɸ = 40°). The thermal performance factor is found to be greater than unity for each configuration studied with DPHE using HSDTs. Correlations have been developed Nusselt number, friction factor and thermal performance factor for Reynolds number varying between 3500–10,500.

Numerical analysis on forced convection enhancement in an annulus using porous ribs and nanoparticle addition to base fluid

Abstract: Miniaturization of electronic equipment has forced researchers to devise more effective methods for dissipating the generated heat in these devices. In this study, two methods, including porous media inserting and adding nanoparticles to the base fluid, are used to improve heat transfer in an annulus heated on both walls. To study porous media insert, porous ribs are used on the outer and inner walls independently. The results show that when porous ribs are placed on the outer wall, although the heat transfer enhances, the pressure drop increment is so considerable that performance number (the ratio of heat transfer enhancement pressure increment, PN) is less than unity for all porous rib heights and porous media permeabilities that are studied. On the other hand, the PN of cases where porous ribs were placed on the inner wall depends on the Darcy number (Da). For example, for ribs with Da=0.1 and Da=0.0001, the maximum performance number, PN=4, occurs at the porous ribs height to hydraulic diameter ratios H/Dh=1 and H/Dh=0.25. Under these conditions, heat transfer is enhanced by two orders of magnitude. It is found that adding 5% nanoparticles to the base fluid in the two aforementioned cases improves the Nusselt number and PN by 10%–40%.

Numerical study of parameters affecting pressure drop of power-law fluid in horizontal annulus for laminar and turbulent flows

Abstract: Efficient hydraulics program of oil and gas wells has a crucial role for the optimization of drilling process. In the present paper, a numerical study of power-law fluid flow through concentric (E = 0.0) and eccentric annulus (E = 0.3, E = 0.6 and E = 0.9) was performed for both laminar and turbulent flow regimes utilizing a finite volume method. The effects of inner pipe rotation, flow behavior index and diameter ratio on the pressure drop were studied; furthermore, the appearance and development of secondary flow as well as its impact on the pressure drop gradient were evaluated. Results indicated that the increment of the inner pipe rotation from 0 to 400 rpm is found to decrease pressure drop gradient for laminar flow in concentric annulus while a negligible effect is observed for turbulent flow. The beginning of secondary flow formation in the wide region part of the eccentric annulus (E = 0.6) induces an increase of 9% and a slight increase in pressure drop gradient for laminar and turbulent flow, respectively. On the other hand, the variation of the flow behavior index and diameter ratio from low to high values caused a dramatic increase in the pressure drop. Streamlines in the annulus showed that the secondary flow is mainly induced by eccentricity of the inner pipe where both high values of diameter ratio and low values of flow behavior index tend to prevent the secondary flow to appear.

Temperature log simulations in high-enthalpy boreholes

Abstract: Temperature logs have important applications in the geothermal industry such as the estimation of the static formation temperature (SFT) and the characterization of fluid loss from a borehole. However, the temperature distribution of the wellbore relies on various factors such as wellbore flow conditions, fluid losses, well layout, heat transfer mechanics within the fluid as well as between the wellbore and the surrounding rock formation, etc. In this context, the numerical approach presented in this paper is applied to investigate the influencing parameters/uncertainties in the interpretation of borehole logging data. To this end, synthetic temperature logs representing different well operation conditions were numerically generated using our newly developed wellbore simulator. Our models account for several complex operation scenarios resulting from the requirements of high-enthalpy wells where different flow conditions, such as mud injection with- and without fluid loss and shut-in, occur in the drill string and the annulus. The simulation results reveal that free convective heat transfer plays an important role in the earlier evolution of the shut-in-time temperature; high accuracy SFT estimation is only possible when long-term shut-in measurements are used. Two other simulation scenarios for a well under injection conditions show that applying simple temperature correction methods on the non-shut-in temperature data could lead to large errors for SFT estimation even at very low injection flow rates. Furthermore, the magnitude of the temperature gradient increase depends on the flow rate, the percentage of fluid loss and the lateral heat transfer between the fluid and the rock formation. As indicated by this study, under low fluid losses ( 20 L/s), the impact of flow rate and the lateral heat transfer on the temperature gradient increase can be ignored. These results provide insights on the key factors influencing the well temperature distribution, which are important for the choice of the drilling data to estimate SFT and the design of the inverse modeling scheme in future studies to determine an accurate SFT profile for the high-enthalpy geothermal environment.

Flow field characters near fracture entrance in supercritical carbon dioxide sand fracturing

Abstract: To investigate the flow field near fracture entrance and promote the development of sand fracturing with carbon dioxide as the working fluid, numerical simulation of multiphase flow was conducted with a 3D geological model considering the compressibility of carbon dioxide. The flow field of carbon dioxide alone was firstly investigated to lay the foundation for the analysis of multiphase flow, and then comparative analysis was conducted on the flow field of both the injecting sand from the pipe and the annulus. The results show that jet fracture with carbon dioxide can achieve a 4.46 MPa pressure boost at the fracture tip compared to the annulus pressure, which theoretically validates the feasibility of the mentioned technology. Sand fracturing can achieve a higher pressure boost in the cavity, while it needs greater pump pressure at the surface. Injecting sand from the annulus could decrease the need for pump pressure by 6.62 MPa at the condition of injecting 25% carbon dioxide from the annulus simultaneously, while the pressure difference between the cavity tip and the annulus decreases as a result.

Establishment and analysis of temperature field of riserless mud recovery system

Abstract: Due to the drill pipe in the Riserless Mud Recovery (RMR) system is exposed to seawater, so the characteristics of the temperature changing are very different from the conventional offshore drilling. Considering temperature is an important factor affecting the annulus pressure, it is necessary to study the variation law of the temperature field of the RMR. In this paper, according to the physical process of the heat transfer in RMR, the mathematical model of the temperature field is established. The Computational Fluid Dynamics (CFD) software is used to simulate the temperature distribution in the drill pipe and the annulus, so that the law of the temperature changing can be observed more intuitively. In order to be more aware of the influencing factors of the temperature field changing, this paper analyzes the influence mechanism of the different discharge capacity and the different injection temperature on temperature changing. Moreover, this paper also analyzes the influence of the annulus temperature on the annulus pressure, which provides a theoretical basis for the well control of RMR.

Gas Lift Operations Require Accurate Predictions of Downhole Annulus Pressure

Abstract: This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 190929, “Gas Lift Annulus Pressure,” by Kenneth Decker, SPE, retired, and Robert P. Sutton, SPE, consultant, prepared for the 2018 SPE Artificial Lift Conference and Exhibition—Americas, The Woodlands, Texas, USA, 28–30 August. The paper has not been peer reviewed. Downhole annulus pressure is required for any gas lift design. This paper presents several methods of determining annulus pressure at depth and helps determine which method is most appropriate for specific conditions. It also provides advice on the accuracy of a combination of different critical properties and compressibility correlations, offers an alternative design technique to account for changing annulus temperature during unloading, and provides guidelines for modeling changes in annulus pressure during unloading. Introduction While many methods of computing gas pressure in a flowing environment are available, what is needed in the case of gas lift is the static annulus pressure at depth. Historically, the method of using average temperature and pressure to compute compressibility factors and assuming linear well-temperature gradients made gas lift design relatively simple. The small errors were tolerable and within the normal design safety mar-gins of operating systems with surface pressures of less than 1,500 psi. When surface injection pressures exceed 1,500 psi, calculations become more important. Computers are now used to calculate downhole annulus pressure, and the designer must trust the number that appears on the computer screen. That trust may not be warranted, depending on the method of calculation. The small errors that creep into computer calculations increase linearly as surface injection pressure increases. Additionally, the choice of which correlation to use to model the critical properties of the gas and which compressibility factor correlation to use also affect the accuracy of the calculation. As a gas lift well transitions from a geothermal to a flowing temperature profile during unloading and lifting, the annulus pressure at depth decreases despite surface injection pressure remaining unchanged. The change in annulus pressure is governed by the volume of gas present in the annulus. Reduction in gas volume decreases pressure. Traditional design techniques ignore this reality and substitute a simplified analogy of valve performance that incurs errors and misconceptions about how the annulus pressure changes during unloading. A more-detailed discussion of these issues and proposed questions for program developers is presented in the complete paper. Annulus Pressure Calculation Methods Methods of determining downhole annulus pressure include monographs, density equations used to full depth with average pressure and temperature, and density equations used in small depth increments with average temperature and pressure within the increment. An examination of one of these monographs is shown in Fig. 1. The choice of which method to use comes with limitations on the accuracy of the predicted pressure at depth.

Numerical Study of a Flow Field Near the Bit for a Coiled-Tubing Partial Underbalanced Drilling Method

Abstract: A new drilling method called coiled-tubing partial underbalanced drilling (CT-PUBD) was proposed in this paper. The method is not only able to enhance rate of penetration (ROP) just like the conventional underbalanced drilling technology but can also maintain borehole stability in the upper formation. In the new method, the wellbore pressure system is divided into two parts by a packer: (1) normal pressure system in the upper formation used to balance formation pressure and maintain borehole stability and (2) an underbalanced pressure system in the annulus near the bit used to enhance ROP. Because the pressure system and the circulation system are different, the cuttings transportation process of the method is different from the conventional way. Therefore, it is essential to study how to carry cuttings away efficiently. The flow field and cuttings distribution in the annulus near the bit were analyzed by computational fluid dynamic (CFD) methods. Cuttings transportation trajectory, velocity distribution, and cuttings concentration distribution were obtained under different holes’ parameters of the backflow device (including holes number, diameter, distance, and angle) and different drilling fluid viscosities. The results show that these parameters all have influence on cuttings carrying efficiency, and the most influential parameters are viscosity, angle, and diameter. According to the result of an orthogonal test, a suitable combination of the holes’ parameters was obtained. In the combination, the value of holes number, diameter, distance, and angle is 4, 50 mm, 300 mm, and 120 deg, respectively. This paper provides a theoretical basis for an optimization design of the new method.

Investigation of oil-water flow in concentric and fully eccentric annuli pipes

Abstract: Experimental investigations are performed on co-current flow of oil (Exxsol D60) and water in concentric and fully eccentric annuli with the inner pipe located at bottom of the outer pipe. The annulus outer and inner pipe have an inside diameter of 99 mm and outside diameter of 50 mm, respectively. This yields a diameter ratio of K = 0.505. The flow conditions studied span mixture velocities and input water cuts in the range 0.50-1.75 m/s and 10-90%, respectively, at pipe inclinations of 0° and 4° upward. Flow regimes have been identified and maps constructed using instantaneous images of the flow from high-speed cameras (shadowgraph) and X-ray chordal holdup measurements along the vertical projection. Flow regimes in the concentric annulus exhibit a higher level of mixing than that observed in the fully eccentric configuration. The transition to dispersed flow occurs at lower mixture velocities in the concentric annulus. Measurements from broad-beam gamma densitometers reveal that the mean water holdup is higher in the fully eccentric annulus for a given mixture velocity and input water cut. The higher water accumulation in this annulus configuration can be attributed to a low velocity region in the narrow gap at the annulus pipe bottom. The frictional pressure gradient in the concentric annulus is higher as compared with the fully eccentric configuration. Peaks in the pressure gradient profile, for a constant mixture velocity, are observed at high water cuts (i.e. WC ≥ 50%) at the transition between dual continuous and dispersed flows. Pressure gradient data are compared with predictions using the homogeneous and two-fluid model. In general, the homogeneous model using a modified Brinkman (Brinkman, H.C., 1952. The viscosity of concentrated suspensions and solutions. J. Chem. Phys., 20(4), 571)/Roscoe (Roscoe, R., 1952. The viscosity of suspensions of rigid spheres. Br. J. Appl. Phys., 3, 267-269) dispersion viscosity model shows the best agreement with data in both concentric and fully eccentric annuli.